%%
%% %CopyrightBegin%
%%
%% SPDX-License-Identifier: Apache-2.0
%%
%% Copyright Ericsson AB 2001-2026. All Rights Reserved.
%%
%% Licensed under the Apache License, Version 2.0 (the "License");
%% you may not use this file except in compliance with the License.
%% You may obtain a copy of the License at
%%
%%     http://www.apache.org/licenses/LICENSE-2.0
%%
%% Unless required by applicable law or agreed to in writing, software
%% distributed under the License is distributed on an "AS IS" BASIS,
%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%% See the License for the specific language governing permissions and
%% limitations under the License.
%%
%% %CopyrightEnd%
%%
-module(sofs).
-moduledoc({file, "../doc/src/sofs.md"}).

-export([from_term/1, from_term/2, from_external/2, empty_set/0,
         is_type/1, set/1, set/2, from_sets/1, relation/1, relation/2,
         a_function/1, a_function/2, family/1, family/2,
         to_external/1, type/1, to_sets/1, no_elements/1,
         specification/2, union/2, intersection/2, difference/2,
         symdiff/2, symmetric_partition/2, product/1, product/2,
         constant_function/2, is_equal/2, is_subset/2, is_sofs_set/1,
         is_set/1, is_empty_set/1, is_disjoint/2]).

-export([union/1, intersection/1, canonical_relation/1]).

-export([relation_to_family/1, domain/1, range/1, field/1,
	 relative_product/1, relative_product/2, relative_product1/2,
	 converse/1, image/2, inverse_image/2, strict_relation/1,
	 weak_relation/1, extension/3, is_a_function/1]).

-export([composite/2, inverse/1]).

-export([restriction/2, restriction/3, drestriction/2, drestriction/3,
         substitution/2, projection/2, partition/1, partition/2,
         partition/3, multiple_relative_product/2, join/4]).

-export([family_to_relation/1, family_specification/2,
         union_of_family/1, intersection_of_family/1,
         family_union/1, family_intersection/1,
         family_domain/1, family_range/1, family_field/1,
         family_union/2, family_intersection/2, family_difference/2,
         partition_family/2, family_projection/2]).

-export([family_to_digraph/1, family_to_digraph/2,
         digraph_to_family/1, digraph_to_family/2]).

%% Shorter names of some functions.
-export([fam2rel/1, rel2fam/1]).

-import(lists,
        [any/2, append/1, flatten/1, foreach/2,
         keysort/2, last/1, map/2, mapfoldl/3, member/2, merge/2,
         reverse/1, reverse/2, sort/1, umerge/1, umerge/2, usort/1]).

-compile({inline, [{family_to_relation,1}, {relation_to_family,1}]}).

-compile({inline, [{rel,2},{a_func,2},{fam,2},{term2set,2}]}).

-compile({inline, [{external_fun,1},{element_type,1}]}).

-compile({inline,
          [{unify_types,2}, {match_types,2},
           {test_rel,3}, {symdiff,3},
           {subst,3}]}).

-compile({inline, [{fam_binop,3}]}).

%% Nope, no is_member, del_member or add_member.
%%
%% See also "Naive Set Theory" by Paul R. Halmos.
%%
%% By convention, erlang:error/1 is called from exported functions.

-define(TAG, 'Set').
-define(ORDTAG, 'OrdSet').

-record(?TAG, {data = [] :: list(), type = type :: term()}).
-record(?ORDTAG, {orddata = {} :: tuple() | atom(),
                  ordtype = type :: term()}).

-define(LIST(S), (S)#?TAG.data).
-define(TYPE(S), (S)#?TAG.type).
-define(SET(L, T), #?TAG{data = L, type = T}).
-define(IS_SET(S), is_record(S, ?TAG)).
-define(IS_UNTYPED_SET(S), ?TYPE(S) =:= ?ANYTYPE).

%% Ordered sets and atoms:
-define(ORDDATA(S), (S)#?ORDTAG.orddata).
-define(ORDTYPE(S), (S)#?ORDTAG.ordtype).
-define(ORDSET(L, T), #?ORDTAG{orddata = L, ordtype = T}).
-define(IS_ORDSET(S), is_record(S, ?ORDTAG)).
-define(ATOM_TYPE, atom).
-define(IS_ATOM_TYPE(T), is_atom(T)). % true for ?ANYTYPE...

%% When IS_SET is true:
-define(ANYTYPE, '_').
-define(BINREL(X, Y), {X, Y}).
-define(IS_RELATION(R), is_tuple(R)).
-define(REL_ARITY(R), tuple_size(R)).
-define(REL_TYPE(I, R), element(I, R)).
-define(SET_OF(X), [X]).
-define(IS_SET_OF(X), is_list(X)).
-define(FAMILY(X, Y), ?BINREL(X, ?SET_OF(Y))).

-export_type([anyset/0, binary_relation/0, external_set/0, a_function/0,
              family/0, relation/0, set_of_sets/0, set_fun/0, spec_fun/0,
              type/0]).
-export_type([ordset/0, a_set/0]).

-doc "Any kind of set (also included are the atomic sets).".
-type(anyset() :: ordset() | a_set()).

-doc "A [binary relation](`m:sofs#binary_relation`).".
-type(binary_relation() :: relation()).

-doc "An [external set](`m:sofs#external_set`).".
-type(external_set() :: term()).

-doc "A [function](`m:sofs#function`).".
-type(a_function() :: relation()).

-doc "A [family](`m:sofs#family`) (of subsets).".
-type(family() :: a_function()).

-doc "An [ordered set](`m:sofs#module-sets-handled-by-this-module`).".
-opaque(ordset() :: #?ORDTAG{}).

-doc "An [n-ary relation](`m:sofs#n_ary_relation`).".
-type(relation() :: a_set()).

-doc "An [unordered set](`m:sofs#module-sets-handled-by-this-module`).".
-opaque(a_set() :: #?TAG{}).

-doc "An [unordered set](`m:sofs#module-sets-handled-by-this-module`)
of unordered sets.".
-type(set_of_sets() :: a_set()).

-doc "A [SetFun](`m:sofs#set_fun`).".
-type(set_fun() :: pos_integer()
                 | {external, fun((external_set()) -> external_set())}
                 | fun((anyset()) -> anyset())).
-type(spec_fun() :: {external, fun((external_set()) -> boolean())}
                  | fun((anyset()) -> boolean())).
-doc "A [type](`m:sofs#type`).".
-type(type() :: term()).

-doc "A tuple where the elements are of type `T`.".
-type(tuple_of(_T) :: tuple()).

%%
%%  Exported functions
%%

%%%
%%% Create sets
%%%

-doc(#{equiv => from_term(Term, '_')}).
-spec(from_term(Term) -> AnySet when
      AnySet :: anyset(),
      Term :: term()).
from_term(T) ->
    Type = case T of
               _ when is_list(T) -> [?ANYTYPE];
               _ -> ?ANYTYPE
           end,
    try setify(T, Type)
    catch _:_ -> erlang:error(badarg)
    end.

-doc """
Creates an element of [Sets](`m:sofs#module-sets-handled-by-this-module`) by
traversing term `Term`, sorting lists, removing duplicates, and deriving or
verifying a [valid type](`m:sofs#valid_type`) for the so obtained external set.

An explicitly specified [type](`m:sofs#type`) `Type` can be used to limit the
depth of the traversal; an atomic type stops the traversal, as shown by the
following example where `"foo"` and `{"foo"}` are left unmodified:

```erlang
1> S = sofs:from_term([{{"foo"},[1,1]},{"foo",[2,2]}],
                      [{atom,[atom]}]),
   sofs:to_external(S).
[{{"foo"},[1]},{"foo",[2]}]
```

`from_term/1` can be used for creating atomic or ordered sets. The only purpose of
such a set is that of later building unordered sets, as all functions in this
module that _do_ anything operate on unordered sets. Creating unordered sets
from a collection of ordered sets can be the way to go if the ordered sets are
big and one does not want to waste heap by rebuilding the elements of the
unordered set. The following example shows that a set can be built "layer by
layer":

```erlang
1> A = sofs:from_term(a).
2> S = sofs:set([1,2,3]).
3> P1 = sofs:from_sets({A,S}).
4> P2 = sofs:from_term({b,[6,5,4]}).
5> Ss = sofs:from_sets([P1,P2]).
6> sofs:to_external(Ss).
[{a,[1,2,3]},{b,[4,5,6]}]
```

Other functions that create sets are `from_external/2` and `from_sets/1`.
Special cases of [`from_term/2`](`from_term/2`) are
[`a_function/1,2`](`a_function/1`), `empty_set/0`, [`family/1,2`](`family/1`),
[`relation/1,2`](`relation/1`), and [`set/1,2`](`set/1`).
""".
-spec(from_term(Term, Type) -> AnySet when
      AnySet :: anyset(),
      Term :: term(),
      Type :: type()).
from_term(L, T) ->
    case is_type(T) of
        true ->
            try setify(L, T)
            catch _:_ -> erlang:error(badarg)
            end;
        false  ->
            erlang:error(badarg)
    end.

-doc """
Creates a set from the [external set](`m:sofs#external_set`) `ExternalSet` and
the [type](`m:sofs#type`) `Type`.

It is assumed that `Type` is a [valid type](`m:sofs#valid_type`) of
`ExternalSet`.

## Examples

```erlang
1> S0 = sofs:from_external([{1,[a,b]},{2,[c]}], [{x,[y]}]).
2> sofs:to_external(sofs:family_to_relation(S0)).
[{1,a},{1,b},{2,c}]
3> S1 = sofs:from_external({a,b,c}, {x,x,x}).
4> sofs:no_elements(S1).
3
```
""".
-spec(from_external(ExternalSet, Type) -> AnySet when
      ExternalSet :: external_set(),
      AnySet :: anyset(),
      Type :: type()).
from_external(L, ?SET_OF(Type)) ->
    ?SET(L, Type);
from_external(T, Type) ->
    ?ORDSET(T, Type).

-doc """
Returns the [untyped empty set](`m:sofs#module-sets-handled-by-this-module`).

`empty_set/0` is equivalent to [`from_term([], ['_'])`](`from_term/2`).

## Examples

```erlang
1> sofs:to_external(sofs:empty_set()).
[]
2> sofs:is_empty_set(sofs:empty_set()).
true
```
""".
-spec(empty_set() -> Set when
      Set :: a_set()).
empty_set() ->
    ?SET([], ?ANYTYPE).

-doc """
Returns `true` if term `Term` is a [type](`m:sofs#type`).

## Examples

```erlang
1> sofs:is_type(atom).
true
2> sofs:is_type([atom]).
true
3> sofs:is_type({a,b}).
true
4> sofs:is_type(42).
false
```
""".
-spec(is_type(Term) -> Bool when
      Bool :: boolean(),
      Term :: term()).
is_type(Atom) when ?IS_ATOM_TYPE(Atom), Atom =/= ?ANYTYPE ->
    true;
is_type(?SET_OF(T)) ->
    is_element_type(T);
is_type(T) when tuple_size(T) > 0 ->
    is_types(tuple_size(T), T);
is_type(_T) ->
    false.

-doc(#{equiv => set(Terms, [atom])}).
-spec(set(Terms) -> Set when
      Set :: a_set(),
      Terms :: [term()]).
set(L) ->
    try usort(L) of
        SL -> ?SET(SL, ?ATOM_TYPE)
    catch _:_ -> erlang:error(badarg)
    end.

-doc """
Creates an [unordered set](`m:sofs#module-sets-handled-by-this-module`).

[`set(L, T)`](`set/2`) is equivalent to
[`from_term(L, T)`](`from_term/2`) if the result is an unordered set.

## Examples

```erlang
1> S1 = sofs:set([3,1,2,3,4], [digit]).
2> sofs:to_external(S1).
[1,2,3,4]
3> S2 = sofs:from_term([1,2,3,4], [digit]).
4> sofs:is_equal(S1, S2).
true
```
""".
-spec(set(Terms, Type) -> Set when
      Set :: a_set(),
      Terms :: [term()],
      Type :: type()).
set(L, ?SET_OF(Type)) when ?IS_ATOM_TYPE(Type), Type =/= ?ANYTYPE ->
    try usort(L) of
        SL -> ?SET(SL, Type)
    catch _:_ -> erlang:error(badarg)
    end;
set(L, ?SET_OF(_) = T) ->
    try setify(L, T)
    catch _:_ -> erlang:error(badarg)
    end;
set(_, _) ->
    erlang:error(badarg).

-doc """
from_sets(AnySet)

Returns the [unordered
set](`m:sofs#module-sets-handled-by-this-module`) containing the sets
of list `ListOfSets`, or returns the [ordered
set](`m:sofs#module-sets-handled-by-this-module`) containing the sets
of the non-empty tuple `TupleOfSets`.

## Examples

Creating an unordered set.

```erlang
1> S1 = sofs:relation([{a,1},{b,2}]).
2> S2 = sofs:relation([{x,3},{y,4}]).
3> S = sofs:from_sets([S1,S2]).
4> sofs:to_external(S).
[[{a,1},{b,2}],[{x,3},{y,4}]]
5> sofs:type(S).
[[{atom,atom}]]
```

Creating an ordered set.

```erlang
1> S1 = sofs:from_term(a).
2> S2 = sofs:from_term(b).
3> S = sofs:from_sets({S1,S2}).
4> sofs:to_external(S).
{a,b}
5> sofs:type(S).
{atom,atom}
```
""".
-spec(from_sets(ListOfSets) -> Set when
      Set :: a_set(),
      ListOfSets :: [anyset()];
               (TupleOfSets) -> Ordset when
      Ordset :: ordset(),
      TupleOfSets :: tuple_of(anyset())).
from_sets(Ss) when is_list(Ss) ->
    case set_of_sets(Ss, [], ?ANYTYPE) of
        {error, Error} ->
            erlang:error(Error);
        Set ->
            Set
    end;
from_sets(Tuple) when is_tuple(Tuple) ->
    case ordset_of_sets(tuple_to_list(Tuple), [], []) of
        error ->
            erlang:error(badarg);
        Set ->
            Set
    end;
from_sets(_) ->
    erlang:error(badarg).

-doc """
Equivalent to [`relation(Tuples, Type)`](`relation/2`), where `Type` is the size
of the first tuple of `Tuples`, if such a tuple exists.

If tuples is `[]`, then `Type` is `2`.

## Examples

```erlang
1> S1 = sofs:relation([{1,a},{1,b},{1,a}]).
2> sofs:to_external(S1).
[{1,a},{1,b}]
3> sofs:type(S1).
[{atom,atom}]
4> sofs:type(sofs:relation([])).
[{atom,atom}]
5> sofs:type(sofs:relation([], 3)).
[{atom,atom,atom}]
6> sofs:relation([a,b,c]).
** exception error: bad argument
     in function  sofs:relation/1
```
""".
-spec(relation(Tuples) -> Relation when
      Relation :: relation(),
      Tuples :: [tuple()]).
relation([]) ->
    ?SET([], ?BINREL(?ATOM_TYPE, ?ATOM_TYPE));
relation(Ts = [T | _]) when is_tuple(T) ->
    try rel(Ts, tuple_size(T))
    catch _:_ -> erlang:error(badarg)
    end;
relation(_) ->
    erlang:error(badarg).

-doc """
Creates a [relation](`m:sofs#relation`).

[`relation(R, T)`](`relation/2`) is equivalent to
[`from_term(R, T)`](`from_term/2`), if T is a [type](`m:sofs#type`)
and the result is a relation.

If `Type` is an integer N, then `[{atom, ..., atom}])`, where the tuple size is N,
is used as type of the relation.

## Examples

```erlang
1> S1 = sofs:relation([{3,blue},{2,green},{3,blue},{1,red}], [{index,color}]).
2> sofs:to_external(S1).
[{1,red},{2,green},{3,blue}]
3> sofs:type(S1).
[{index,color}]
4> sofs:type(sofs:relation([{1,a},{1,b}], 2)).
[{atom,atom}]
5> sofs:type(sofs:relation([], 3)).
[{atom,atom,atom}]
```
""".
-spec(relation(Tuples, Type) -> Relation when
      N :: integer(),
      Type :: N | type(),
      Relation :: relation(),
      Tuples :: [tuple()]).
relation(Ts, TS) ->
    try rel(Ts, TS)
    catch _:_ -> erlang:error(badarg)
    end.

-doc(#{equiv => a_function(Tuples, [{atom, atom}])}).
-spec(a_function(Tuples) -> Function when
      Function :: a_function(),
      Tuples :: [tuple()]).
a_function(Ts) ->
    try func(Ts, ?BINREL(?ATOM_TYPE, ?ATOM_TYPE)) of
        Bad when is_atom(Bad) ->
            erlang:error(Bad);
        Set ->
            Set
    catch _:_ -> erlang:error(badarg)
    end.

-doc """
Creates a [function](`m:sofs#function`).

[`a_function(F, T)`](`a_function/2`) is equivalent to
[`from_term(F, T)`](`from_term/2`) if the result is a function.

## Examples

```erlang
1> sofs:is_a_function(sofs:a_function([{1,a},{2,b},{3,c}])).
true
2> sofs:a_function([{1,a},{1,b}]).
** exception error: bad_function
     in function  sofs:a_function/1
```
""".
-spec(a_function(Tuples, Type) -> Function when
      Function :: a_function(),
      Tuples :: [tuple()],
      Type :: type()).
a_function(Ts, T) ->
    try a_func(Ts, T) of
	Bad when is_atom(Bad) ->
	    erlang:error(Bad);
	Set ->
	    Set
    catch _:_ -> erlang:error(badarg)
    end.

-doc(#{equiv => family(Tuples, [{atom, [atom]}])}).
-spec(family(Tuples) -> Family when
      Family :: family(),
      Tuples :: [tuple()]).
family(Ts) ->
    try fam2(Ts, ?FAMILY(?ATOM_TYPE, ?ATOM_TYPE)) of
        Bad when is_atom(Bad) ->
            erlang:error(Bad);
        Set ->
	    Set
    catch _:_ -> erlang:error(badarg)
    end.

-doc """
Creates a [family of subsets](`m:sofs#family`).

[`family(F, T)`](`family/2`) is equivalent to
[`from_term(F, T)`](`from_term/2`) if the result is a family.

## Examples

```erlang
1> S = sofs:family([{1,[a,b]},{2,[c]}], [{index,[value]}]).
2> sofs:to_external(sofs:family_to_relation(S)).
[{1,a},{1,b},{2,c}]
3> S = sofs:family([{1,[a,b]},{1,[c]}], [{index,[value]}]).
** exception error: bad_function
     in function  sofs:family/2
```
""".
-spec(family(Tuples, Type) -> Family when
      Family :: family(),
      Tuples :: [tuple()],
      Type :: type()).
family(Ts, T) ->
    try fam(Ts, T) of
	Bad when is_atom(Bad) ->
	    erlang:error(Bad);
	Set ->
	    Set
    catch _:_ -> erlang:error(badarg)
    end.

%%%
%%% Functions on sets.
%%%

-doc """
Returns the [external set](`m:sofs#external_set`) of an atomic, ordered, or
unordered set.

```erlang
1> sofs:to_external(sofs:set([2,3,1])).
[1,2,3]
2> sofs:to_external(sofs:from_term({2,3,1})).
{2,3,1}
3> sofs:to_external(sofs:from_term(a)).
a
```
""".
-spec(to_external(AnySet) -> ExternalSet when
      ExternalSet :: external_set(),
      AnySet :: anyset()).
to_external(S) when ?IS_SET(S) ->
    ?LIST(S);
to_external(S) when ?IS_ORDSET(S) ->
    ?ORDDATA(S).

-doc """
Returns the [type](`m:sofs#type`) of an atomic, ordered, or unordered set.

## Examples

Unordered sets.

```erlang
1> sofs:type(sofs:empty_set()).
['_']
2> sofs:type(sofs:set([], [color])).
[color]
3> sofs:type(sofs:set([red,green,blue], [color])).
[color]
4> sofs:type(sofs:set([1,2,3])).
[atom]
```

Ordered sets.

```erlang
1> sofs:type(sofs:from_term({a,b,c})).
{atom,atom,atom}
2> sofs:type(sofs:from_term({1.0,2.5,-1.0}, {x,y,z})).
{x,y,z}
```

Atomic sets.

```erlang
1> sofs:type(sofs:from_term(a)).
atom
2> sofs:type(sofs:from_term(1, index)).
index
```
""".
-spec(type(AnySet) -> Type when
      AnySet :: anyset(),
      Type :: type()).
type(S) when ?IS_SET(S) ->
    ?SET_OF(?TYPE(S));
type(S) when ?IS_ORDSET(S) ->
    ?ORDTYPE(S).

-doc """
Returns the elements of the ordered set `ASet` as a tuple of sets, and the
elements of the unordered set `ASet` as a sorted list of sets without
duplicates.

## Examples

```erlang
1> [S1,S2,S3] = sofs:to_sets(sofs:set([3,2,1])).
2> {sofs:to_external(S1),sofs:to_external(S2),sofs:to_external(S3)}.
{1,2,3}
3> {S4,S5,S6} = sofs:to_sets(sofs:from_term({c,a,b})).
4> {sofs:to_external(S4),sofs:to_external(S5),sofs:to_external(S6)}.
{c,a,b}
```
""".
-spec(to_sets(ASet) -> Sets when
      ASet :: a_set() | ordset(),
      Sets :: tuple_of(AnySet) | [AnySet],
      AnySet :: anyset()).
to_sets(S) when ?IS_SET(S) ->
    case ?TYPE(S) of
        ?SET_OF(Type) -> list_of_sets(?LIST(S), Type, []);
        Type -> list_of_ordsets(?LIST(S), Type, [])
    end;
to_sets(S) when ?IS_ORDSET(S), is_tuple(?ORDTYPE(S)) ->
    tuple_of_sets(tuple_to_list(?ORDDATA(S)), tuple_to_list(?ORDTYPE(S)), []);
to_sets(S) when ?IS_ORDSET(S) ->
    erlang:error(badarg).

-doc """
Returns the number of elements of the ordered or unordered set `ASet`.

## Examples

```erlang
1> sofs:no_elements(sofs:set([a,b,c])).
3
2> sofs:no_elements(sofs:relation([{1,a}])).
1
3> sofs:no_elements(sofs:from_term({1,2,3,4})).
4
4> sofs:no_elements(sofs:from_term(a)).
** exception error: bad argument
     in function  sofs:no_elements/1
```
""".
-spec(no_elements(ASet) -> NoElements when
      ASet :: a_set() | ordset(),
      NoElements :: non_neg_integer()).
no_elements(S) when ?IS_SET(S) ->
    length(?LIST(S));
no_elements(S) when ?IS_ORDSET(S), is_tuple(?ORDTYPE(S)) ->
    tuple_size(?ORDDATA(S));
no_elements(S) when ?IS_ORDSET(S) ->
    erlang:error(badarg).

-doc """
Returns the set containing every element of `Set1` for which `Fun` returns
`true`.

If `Fun` is a tuple `{external, Fun2}`, `Fun2` is applied to the
[external set](`m:sofs#external_set`) of each element, otherwise `Fun` is
applied to each element.

## Examples

```erlang
1> R1 = sofs:relation([{a,1},{b,2}]).
2> R2 = sofs:relation([{x,1},{x,2},{y,3}]).
3> S1 = sofs:from_sets([R1,R2]).
4> S2 = sofs:specification(fun sofs:is_a_function/1, S1).
5> sofs:to_external(S2).
[[{a,1},{b,2}]]
```

Using an external fun.

```erlang
1> S1 = sofs:set([1,2,3,4,5,6,7]).
2> SetFun = {external,fun(E) -> E rem 2 =:= 0 end}.
3> S2 = sofs:specification(SetFun, S1).
4> sofs:to_external(S2).
[2,4,6]
```
""".
-spec(specification(Fun, Set1) -> Set2 when
      Fun :: spec_fun(),
      Set1 :: a_set(),
      Set2 :: a_set()).
specification(Fun, S) when ?IS_SET(S) ->
    Type = ?TYPE(S),
    R = case external_fun(Fun) of
	    false ->
		spec(?LIST(S), Fun, element_type(Type), []);
	    XFun ->
		specification(?LIST(S), XFun, [])
	end,
    case R of
	SL when is_list(SL) ->
	    ?SET(SL, Type);
	Bad ->
	    erlang:error(Bad)
    end.

-doc """
Returns the [union](`m:sofs#union`) of `Set1` and `Set2`.

## Examples

```erlang
1> S1 = sofs:set([a,b,c]).
2> S2 = sofs:set([c,d,1,2,3]).
3> S3 = sofs:union(S1, S2).
4> sofs:to_external(S3).
[1,2,3,a,b,c,d]
```
""".
-spec(union(Set1, Set2) -> Set3 when
      Set1 :: a_set(),
      Set2 :: a_set(),
      Set3 :: a_set()).
union(S1, S2) when ?IS_SET(S1), ?IS_SET(S2) ->
    case unify_types(?TYPE(S1), ?TYPE(S2)) of
        [] -> erlang:error(type_mismatch);
        Type ->  ?SET(umerge(?LIST(S1), ?LIST(S2)), Type)
    end.

-doc """
Returns the [intersection](`m:sofs#intersection`) of `Set1` and `Set2`.

## Examples

```erlang
1> S1 = sofs:set([a,b,c]).
2> S2 = sofs:set([b,c,d]).
3> S3 = sofs:intersection(S1, S2).
4> sofs:to_external(S3).
[b,c]
```
""".
-spec(intersection(Set1, Set2) -> Set3 when
      Set1 :: a_set(),
      Set2 :: a_set(),
      Set3 :: a_set()).
intersection(S1, S2) when ?IS_SET(S1), ?IS_SET(S2) ->
    case unify_types(?TYPE(S1), ?TYPE(S2)) of
        [] -> erlang:error(type_mismatch);
        Type ->  ?SET(intersection(?LIST(S1), ?LIST(S2), []), Type)
    end.

-doc """
Returns the [difference](`m:sofs#difference`) of the sets `Set1` and `Set2`.

## Examples

```erlang
1> S0 = sofs:set([a,b,c,d]).
2> S1 = sofs:set([c,d,e,f]).
3> sofs:to_external(sofs:difference(S0, S1)).
[a,b]
4> sofs:to_external(sofs:difference(S1, S0)).
[e,f]
```
""".
-spec(difference(Set1, Set2) -> Set3 when
      Set1 :: a_set(),
      Set2 :: a_set(),
      Set3 :: a_set()).
difference(S1, S2) when ?IS_SET(S1), ?IS_SET(S2) ->
    case unify_types(?TYPE(S1), ?TYPE(S2)) of
        [] -> erlang:error(type_mismatch);
        Type ->  ?SET(difference(?LIST(S1), ?LIST(S2), []), Type)
    end.

-doc """
Returns the [symmetric difference](`m:sofs#symmetric_difference`) (or the
Boolean sum) of `Set1` and `Set2`.

## Examples

```erlang
1> S1 = sofs:set([1,2,3]).
2> S2 = sofs:set([2,3,4]).
3> P = sofs:symdiff(S1, S2).
4> sofs:to_external(P).
[1,4]
```
""".
-spec(symdiff(Set1, Set2) -> Set3 when
      Set1 :: a_set(),
      Set2 :: a_set(),
      Set3 :: a_set()).
symdiff(S1, S2) when ?IS_SET(S1), ?IS_SET(S2) ->
    case unify_types(?TYPE(S1), ?TYPE(S2)) of
        [] -> erlang:error(type_mismatch);
        Type ->  ?SET(symdiff(?LIST(S1), ?LIST(S2), []), Type)
    end.

-doc """
Returns the symmetric partition of `Set1` and `Set2`.

Returns a triple of sets:

- `Set3` contains the elements of `Set1` that do not belong to `Set2`.
- `Set4` contains the elements of `Set1` that belong to `Set2`.
- `Set5` contains the elements of `Set2` that do not belong to `Set1`.

## Examples

```erlang
1> S1 = sofs:set([a,b,c]).
2> S2 = sofs:set([c,d,e]).
3> {S3,S4,S5} = sofs:symmetric_partition(S1, S2).
4> {sofs:to_external(S3),sofs:to_external(S4),sofs:to_external(S5)}.
{[a,b],[c],[d,e]}
```
""".
-spec(symmetric_partition(Set1, Set2) -> {Set3, Set4, Set5} when
      Set1 :: a_set(),
      Set2 :: a_set(),
      Set3 :: a_set(),
      Set4 :: a_set(),
      Set5 :: a_set()).
symmetric_partition(S1, S2) when ?IS_SET(S1), ?IS_SET(S2) ->
    case unify_types(?TYPE(S1), ?TYPE(S2)) of
        [] -> erlang:error(type_mismatch);
        Type ->  sympart(?LIST(S1), ?LIST(S2), [], [], [], Type)
    end.

-doc """
Returns the [Cartesian product](`m:sofs#Cartesian_product`) of `Set1` and
`Set2`.

## Examples

```erlang
1> S1 = sofs:set([1,2]).
2> S2 = sofs:set([a,b]).
3> R = sofs:product(S1, S2).
4> sofs:to_external(R).
[{1,a},{1,b},{2,a},{2,b}]
```

[`product(S1, S2)`](`product/2`) is equivalent to
[`product({S1, S2})`](`product/1`).
""".
-spec(product(Set1, Set2) -> BinRel when
      BinRel :: binary_relation(),
      Set1 :: a_set(),
      Set2 :: a_set()).
product(S1, S2) when ?IS_SET(S1), ?IS_SET(S2) ->
    if
        ?TYPE(S1) =:= ?ANYTYPE -> S1;
        ?TYPE(S2) =:= ?ANYTYPE -> S2;
        true ->
	    F = fun(E) -> {0, E} end,
	    T = ?BINREL(?TYPE(S1), ?TYPE(S2)),
	    ?SET(relprod(map(F, ?LIST(S1)), map(F, ?LIST(S2))), T)
    end.

-doc """
Returns the [Cartesian product](`m:sofs#Cartesian_product_tuple`) of the
non-empty tuple of sets `TupleOfSets`.

If (x\[1], ..., x\[n]) is an element of the n-ary relation `Relation`,
then x\[i] is drawn from element i of `TupleOfSets`.

## Examples

```erlang
1> S1 = sofs:set([a,b]).
2> S2 = sofs:set([1,2]).
3> S3 = sofs:set([x,y]).
4> P3 = sofs:product({S1,S2,S3}).
5> sofs:to_external(P3).
[{a,1,x},{a,1,y},{a,2,x},{a,2,y},{b,1,x},{b,1,y},{b,2,x},{b,2,y}]
```
""".
-spec(product(TupleOfSets) -> Relation when
      Relation :: relation(),
      TupleOfSets :: tuple_of(a_set())).
product({S1, S2}) ->
    product(S1, S2);
product(T) when is_tuple(T) ->
    Ss = tuple_to_list(T),
    try sets_to_list(Ss) of
        [] ->
            erlang:error(badarg);
        L ->
            Type = types(Ss, []),
            case member([], L) of
                true ->
		    empty_set();
                false ->
                    ?SET(reverse(prod(L, [], [])), Type)
            end
    catch _:_ -> erlang:error(badarg)
    end.

-doc """
Creates the [function](`m:sofs#function`) that maps each element of set `Set`
onto `AnySet`.

## Examples

```erlang
1> S = sofs:set([a,b]).
2> E = sofs:from_term(1).
3> R = sofs:constant_function(S, E).
4> sofs:to_external(R).
[{a,1},{b,1}]
```
""".
-spec(constant_function(Set, AnySet) -> Function when
      AnySet :: anyset(),
      Function :: a_function(),
      Set :: a_set()).
constant_function(S, E) when ?IS_SET(S) ->
    case {?TYPE(S), is_sofs_set(E)} of
	{?ANYTYPE, true} -> S;
	{Type, true} ->
	    NType = ?BINREL(Type, type(E)),
	    ?SET(constant_function(?LIST(S), to_external(E), []), NType);
	_ -> erlang:error(badarg)
    end;
constant_function(S, _) when ?IS_ORDSET(S) ->
    erlang:error(badarg).

-doc """
Returns `true` if `AnySet1` and `AnySet2` are [equal](`m:sofs#equal`), otherwise
`false`.

## Examples

The following example shows that `==/2` is used when comparing sets for
equality:

```erlang
1> S1 = sofs:set([1.0]).
2> S2 = sofs:set([1]).
3> sofs:is_equal(S1, S2).
true
```
""".
-spec(is_equal(AnySet1, AnySet2) -> Bool when
      AnySet1 :: anyset(),
      AnySet2 :: anyset(),
      Bool :: boolean()).
is_equal(S1, S2) when ?IS_SET(S1), ?IS_SET(S2) ->
    case match_types(?TYPE(S1), ?TYPE(S2)) of
        true  -> ?LIST(S1) == ?LIST(S2);
        false -> erlang:error(type_mismatch)
    end;
is_equal(S1, S2) when ?IS_ORDSET(S1), ?IS_ORDSET(S2) ->
    case match_types(?ORDTYPE(S1), ?ORDTYPE(S2)) of
        true  -> ?ORDDATA(S1) == ?ORDDATA(S2);
        false -> erlang:error(type_mismatch)
    end;
is_equal(S1, S2) when ?IS_SET(S1), ?IS_ORDSET(S2) ->
    erlang:error(type_mismatch);
is_equal(S1, S2) when ?IS_ORDSET(S1), ?IS_SET(S2) ->
    erlang:error(type_mismatch).

-doc """
Returns `true` if `Set1` is a [subset](`m:sofs#subset`) of `Set2`; otherwise,
returns `false`.

```erlang
1> S1 = sofs:set([2,4,6]).
2> S2 = sofs:set([1,2,3,4,5,6]).
3> sofs:is_subset(S1, S2).
true
4> sofs:is_subset(S2, S1).
false
5> sofs:is_subset(S1, S1).
true
6> S3 = sofs:relation([{1,a},{2,b}]).
7> S4 = sofs:relation([{1,a}]).
8> sofs:is_subset(S4, S3).
true
9> sofs:is_subset(S3, S1).
** exception error: type_mismatch
     in function  sofs:is_subset/2
```
""".
-spec(is_subset(Set1, Set2) -> Bool when
      Bool :: boolean(),
      Set1 :: a_set(),
      Set2 :: a_set()).
is_subset(S1, S2) when ?IS_SET(S1), ?IS_SET(S2) ->
    case match_types(?TYPE(S1), ?TYPE(S2)) of
        true  -> subset(?LIST(S1), ?LIST(S2));
        false -> erlang:error(type_mismatch)
    end.

-doc """
Returns `true` if `Term` appears to be an
[unordered set](`m:sofs#module-sets-handled-by-this-module`),
an ordered set, or an atomic set; otherwise, returns `false`.

Note that this function will return `true` for any term that
coincides with the representation of a `sofs` set. See also note on
[data types](`e:system:data_types.md#no_user_types`).

## Examples

```erlang
1> sofs:is_sofs_set(sofs:set([a,b,c])).
true
2> sofs:is_sofs_set(sofs:from_term(a)).
true
3> sofs:is_sofs_set(sofs:from_term({a,b,c})).
true
4> sofs:is_sofs_set(42).
false
```
""".
-spec(is_sofs_set(Term) -> Bool when
      Bool :: boolean(),
      Term :: term()).
is_sofs_set(S) when ?IS_SET(S) ->
    true;
is_sofs_set(S) when ?IS_ORDSET(S) ->
    true;
is_sofs_set(_S) ->
    false.

-doc """
Returns `true` if `AnySet` appears to be an
[unordered set](`m:sofs#module-sets-handled-by-this-module`), and `false` if `AnySet` is an ordered
set or an atomic set or any other term.

Note that the test is shallow and this function will return `true` for any term
that coincides with the representation of an unordered set. See also note on
[data types](`e:system:data_types.md#no_user_types`).

## Examples

```erlang
1> sofs:is_set(sofs:set([1,2,3])).
true
2> sofs:is_set(sofs:from_term({a,b,c})).
false
3> sofs:is_set(42).
** exception error: no function clause matching sofs:is_set(42)
```
""".
-spec(is_set(AnySet) -> Bool when
      AnySet :: anyset(),
      Bool :: boolean()).
is_set(S) when ?IS_SET(S) ->
    true;
is_set(S) when ?IS_ORDSET(S) ->
    false.

-doc """
Returns `true` if `AnySet` is an empty unordered set; otherwise, returns `false`.

## Examples

```erlang
1> sofs:is_empty_set(sofs:empty_set()).
true
2> sofs:is_empty_set(sofs:set([a,b])).
false
```
""".
-spec(is_empty_set(AnySet) -> Bool when
      AnySet :: anyset(),
      Bool :: boolean()).
is_empty_set(S) when ?IS_SET(S) ->
    ?LIST(S) =:= [];
is_empty_set(S) when ?IS_ORDSET(S) ->
    false.

-doc """
Returns `true` if `Set1` and `Set2` are [disjoint](`m:sofs#disjoint`); otherwise,
returns `false`.

## Examples

```erlang
1> S1 = sofs:set([a,b,c]).
2> S2 = sofs:set([c,d,e]).
3> S3 = sofs:set([1,2,3]).
4> sofs:is_disjoint(S1, S2).
false
5> sofs:is_disjoint(S1, S3).
true
6> sofs:is_disjoint(sofs:set([1,2,3]), sofs:relation([{a,b}])).
** exception error: type_mismatch
     in function  sofs:is_disjoint/2
```
""".
-spec(is_disjoint(Set1, Set2) -> Bool when
      Bool :: boolean(),
      Set1 :: a_set(),
      Set2 :: a_set()).
is_disjoint(S1, S2) when ?IS_SET(S1), ?IS_SET(S2) ->
    case match_types(?TYPE(S1), ?TYPE(S2)) of
        true ->
            case ?LIST(S1) of
                [] -> true;
                [A | As] -> disjoint(?LIST(S2), A, As)
            end;
        false -> erlang:error(type_mismatch)
    end.

%%%
%%% Functions on set-of-sets.
%%%

-doc """
Returns the [union](`m:sofs#union_n`) of the set of sets `SetOfSets`.

## Examples

```erlang
1> S1 = sofs:set([a,b,c]).
2> S2 = sofs:set([b,1,2]).
3> S3 = sofs:set([a,d,e]).
4> S4 = sofs:from_sets([S1,S2,S3]).
5> S5 = sofs:union(S4).
6> sofs:to_external(S5).
[1,2,a,b,c,d,e]
```
""".
-spec(union(SetOfSets) -> Set when
      Set :: a_set(),
      SetOfSets :: set_of_sets()).
union(Sets) when ?IS_SET(Sets) ->
    case ?TYPE(Sets) of
        ?SET_OF(Type) -> ?SET(lunion(?LIST(Sets)), Type);
        ?ANYTYPE -> Sets;
        _ -> erlang:error(badarg)
    end.

-doc """
Returns the [intersection](`m:sofs#intersection_n`) of the set of sets
`SetOfSets`.

Intersecting an empty set of sets exits the process with a `badarg` message.

## Examples

```erlang
1> S1 = sofs:set([a,b,c]).
2> S2 = sofs:set([b,c,d,e]).
3> S3 = sofs:set([a,b,c,d]).
4> S4 = sofs:from_sets([S1,S2,S3]).
5> S5 = sofs:intersection(S4).
6> sofs:to_external(S5).
[b,c]
7> S6 = sofs:from_sets([]).
8> sofs:intersection(S6).
** exception error: bad argument
     in function  sofs:intersection/1
```
""".
-spec(intersection(SetOfSets) -> Set when
      Set :: a_set(),
      SetOfSets :: set_of_sets()).
intersection(Sets) when ?IS_SET(Sets) ->
    case ?LIST(Sets) of
        [] -> erlang:error(badarg);
        [L | Ls] ->
            case ?TYPE(Sets) of
                ?SET_OF(Type) ->
                    ?SET(lintersection(Ls, L), Type);
                _ -> erlang:error(badarg)
            end
    end.

-doc """
Returns the binary relation containing the elements (E, Set) such that Set
belongs to `SetOfSets` and E belongs to Set.

If `SetOfSets` is a [partition](`m:sofs#partition`) of a set X and R is the
equivalence relation in X induced by `SetOfSets`, then the returned relation is the
[canonical map](`m:sofs#canonical_map`) from X onto the equivalence classes with
respect to R.

## Examples

```erlang
1> Ss = sofs:from_term([[a,b],[b,c]]).
2> CR = sofs:canonical_relation(Ss).
3> sofs:to_external(CR).
[{a,[a,b]},{b,[a,b]},{b,[b,c]},{c,[b,c]}]
```
""".
-spec(canonical_relation(SetOfSets) -> BinRel when
      BinRel :: binary_relation(),
      SetOfSets :: set_of_sets()).
canonical_relation(Sets) when ?IS_SET(Sets) ->
    ST = ?TYPE(Sets),
    case ST of
        ?SET_OF(?ANYTYPE) -> empty_set();
        ?SET_OF(Type) ->
            ?SET(can_rel(?LIST(Sets), []), ?BINREL(Type, ST));
        ?ANYTYPE -> Sets;
        _ -> erlang:error(badarg)
    end.

%%%
%%% Functions on binary relations only.
%%%

-doc false.
-spec(rel2fam(BinRel) -> Family when
      Family :: family(),
      BinRel :: binary_relation()).
rel2fam(R) ->
    relation_to_family(R).

-doc """
Returns [family](`m:sofs#family`) `Family` such that the index set is equal to
the [domain](`m:sofs#domain`) of the binary relation `BinRel`, and `Family`\[i]
is the [image](`m:sofs#image`) of the set of i under `BinRel`.

## Examples

```erlang
1> R = sofs:relation([{b,1},{c,2},{c,3}]).
2> F = sofs:relation_to_family(R).
3> sofs:to_external(F).
[{b,[1]},{c,[2,3]}]
```
""".
-spec(relation_to_family(BinRel) -> Family when
      Family :: family(),
      BinRel :: binary_relation()).
%% Inlined.
relation_to_family(R) when ?IS_SET(R) ->
    case ?TYPE(R) of
        ?BINREL(DT, RT) ->
            ?SET(rel2family(?LIST(R)), ?FAMILY(DT, RT));
        ?ANYTYPE -> R;
        _Else    -> erlang:error(badarg)
    end.

-doc """
Returns the [domain](`m:sofs#domain`) of the binary relation `BinRel`.

## Examples

```erlang
1> R = sofs:relation([{1,a},{1,b},{2,b},{2,c}]).
2> S = sofs:domain(R).
3> sofs:to_external(S).
[1,2]
```
""".
-spec(domain(BinRel) -> Set when
      BinRel :: binary_relation(),
      Set :: a_set()).
domain(R) when ?IS_SET(R) ->
    case ?TYPE(R) of
        ?BINREL(DT, _)  -> ?SET(dom(?LIST(R)), DT);
        ?ANYTYPE -> R;
        _Else    -> erlang:error(badarg)
    end.

-doc """
Returns the [range](`m:sofs#range`) of the binary relation `BinRel`.

## Examples

```erlang
1> R = sofs:relation([{1,a},{1,b},{2,b},{2,c}]).
2> S = sofs:range(R).
3> sofs:to_external(S).
[a,b,c]
```
""".
-spec(range(BinRel) -> Set when
      BinRel :: binary_relation(),
      Set :: a_set()).
range(R) when ?IS_SET(R) ->
    case ?TYPE(R) of
        ?BINREL(_, RT)  -> ?SET(ran(?LIST(R),  []), RT);
        ?ANYTYPE -> R;
        _ -> erlang:error(badarg)
    end.

-doc """
Returns the [field](`m:sofs#field`) of the binary relation `BinRel`.

## Examples

```erlang
1> R = sofs:relation([{1,a},{1,b},{2,b},{2,c}]).
2> S = sofs:field(R).
3> sofs:to_external(S).
[1,2,a,b,c]
```

[`field(R)`](`field/1`) is equivalent to
[`union(domain(R), range(R))`](`union/2`).
""".
-spec(field(BinRel) -> Set when
      BinRel :: binary_relation(),
      Set :: a_set()).
%% In "Introduction to LOGIC", Suppes defines the field of a binary
%% relation to be the union of the domain and the range (or
%% counterdomain).
field(R) ->
    union(domain(R), range(R)).

-doc """
Returns [relative product](`m:sofs#tuple_relative_product`) of the ordered set
(R\[i], ..., R\[n]) and the relation of equality between the elements of the
[Cartesian product](`m:sofs#Cartesian_product_tuple`) of the ranges of R\[i],
range R\[1] × ... × range R\[n].

## Examples

```erlang
1> TR = sofs:relation([{1,a},{1,aa},{2,b},{4,x}]).
2> R1 = sofs:relation([{1,u},{2,v},{3,c}]).
3> R2 = sofs:relative_product([TR, R1]).
4> sofs:to_external(R2).
[{1,{a,u}},{1,{aa,u}},{2,{b,v}}]
```
""".
-spec(relative_product(ListOfBinRels) -> BinRel2 when
      ListOfBinRels :: [BinRel, ...],
      BinRel :: binary_relation(),
      BinRel2 :: binary_relation()).
%% The following clause is kept for backward compatibility.
%% The list is due to Dialyzer's specs.
relative_product(RT) when is_tuple(RT) ->
    relative_product(tuple_to_list(RT));
relative_product(RL) when is_list(RL) ->
    case relprod_n(RL, foo, false, false) of
        {error, Reason} ->
            erlang:error(Reason);
        Reply ->
            Reply
    end.

-doc """
relative_product(ListOrRel, BinRel1)

Returns the [relative product](`m:sofs#tuple_relative_product`).

If `ListOrRel` is a non-empty list [R[1], ..., R[n]] of binary relations
and `BinRel1` is a binary relation, then `BinRel2` is the
[relative product](`m:sofs#tuple_relative_product`) of the ordered set
(R\[i], ..., R\[n]) and `BinRel1`.

Notice that [`relative_product([R1], R2)`](`relative_product/2`) is different
from [`relative_product(R1, R2)`](`relative_product/2`); the list of one element
is not identified with the element itself.

## Examples

```erlang
1> R1 = sofs:relation([{a,b},{c,a}]).
2> R2 = sofs:relation([{a,1},{a,2}]).
3> S = sofs:from_term([{{b,1},b1},{{b,2},b2}]).
4> R3 = sofs:relative_product([R1,R2], S).
5> sofs:to_external(R3).
[{a,b1},{a,b2}]
```

If `ListOrRel` is a binary relation, then `BinRel2` is the
[relative product](`m:sofs#relative_product`) of the binary
relations `ListOfRel` and `BinRel1`.

## Examples

```erlang
1> R1 = sofs:relation([{a,b}, {c,a}]).
2> R2 = sofs:relation([{a,1}, {a,2}]).
3> R3 = sofs:relative_product(R1, R2).
4> sofs:to_external(R3).
[{c,1},{c,2}]
```
""".
-spec(relative_product(ListOfBinRels, BinRel1) -> BinRel2 when
      ListOfBinRels :: [BinRel, ...],
      BinRel :: binary_relation(),
      BinRel1 :: binary_relation(),
      BinRel2 :: binary_relation();
                      (BinRel1, BinRel2) -> BinRel3 when
      BinRel1 :: binary_relation(),
      BinRel2 :: binary_relation(),
      BinRel3 :: binary_relation()).
relative_product(R1, R2) when ?IS_SET(R1), ?IS_SET(R2) ->
    relative_product1(converse(R1), R2);
%% The following clause is kept for backward compatibility.
%% The list is due to Dialyzer's specs.
relative_product(RT, R) when is_tuple(RT), ?IS_SET(R) ->
    relative_product(tuple_to_list(RT), R);
relative_product(RL, R) when is_list(RL), ?IS_SET(R) ->
    EmptyR = case ?TYPE(R) of
                 ?BINREL(_, _) -> ?LIST(R) =:= [];
                 ?ANYTYPE -> true;
                 _ -> erlang:error(badarg)
             end,
    case relprod_n(RL, R, EmptyR, true) of
        {error, Reason} ->
            erlang:error(Reason);
        Reply ->
            Reply
    end.

-doc """
Returns the [relative product](`m:sofs#relative_product`) of the
[converse](`m:sofs#converse`) of the binary relation `BinRel1` and the binary
relation `BinRel2`.

## Examples

```erlang
1> R1 = sofs:relation([{1,a},{1,aa},{2,b}]).
2> R2 = sofs:relation([{1,u},{2,v},{3,c}]).
3> R3 = sofs:relative_product1(R1, R2).
4> sofs:to_external(R3).
[{a,u},{aa,u},{b,v}]
```

[`relative_product1(R1, R2)`](`relative_product1/2`) is equivalent to
[`relative_product(converse(R1), R2)`](`relative_product/2`).
""".
-spec(relative_product1(BinRel1, BinRel2) -> BinRel3 when
      BinRel1 :: binary_relation(),
      BinRel2 :: binary_relation(),
      BinRel3 :: binary_relation()).
relative_product1(R1, R2) when ?IS_SET(R1), ?IS_SET(R2) ->
    {DTR1, RTR1} = case ?TYPE(R1) of
                     ?BINREL(_, _) = R1T -> R1T;
                     ?ANYTYPE -> {?ANYTYPE, ?ANYTYPE};
                     _ -> erlang:error(badarg)
                 end,
    {DTR2, RTR2} = case ?TYPE(R2) of
                     ?BINREL(_, _) = R2T -> R2T;
                     ?ANYTYPE -> {?ANYTYPE, ?ANYTYPE};
                     _ -> erlang:error(badarg)
                 end,
    case match_types(DTR1, DTR2) of
        true when DTR1 =:= ?ANYTYPE -> R1;
        true when DTR2 =:= ?ANYTYPE -> R2;
        true -> ?SET(relprod(?LIST(R1), ?LIST(R2)), ?BINREL(RTR1, RTR2));
        false -> erlang:error(type_mismatch)
    end.

-doc """
Returns the [converse](`m:sofs#converse`) of the binary relation `BinRel1`.

See `inverse/1` for a similar function that applies only to invertible
functions.

## Examples

```erlang
1> R1 = sofs:relation([{1,a},{2,b},{3,a}]).
2> R2 = sofs:converse(R1).
3> sofs:to_external(R2).
[{a,1},{a,3},{b,2}]
```
""".
-spec(converse(BinRel1) -> BinRel2 when
      BinRel1 :: binary_relation(),
      BinRel2 :: binary_relation()).
converse(R) when ?IS_SET(R) ->
    case ?TYPE(R) of
        ?BINREL(DT, RT) -> ?SET(converse(?LIST(R), []), ?BINREL(RT, DT));
        ?ANYTYPE -> R;
        _ -> erlang:error(badarg)
    end.

-doc """
Returns the [image](`m:sofs#image`) of set `Set1` under the binary relation
`BinRel`.

## Examples

```erlang
1> R = sofs:relation([{1,a},{2,b},{2,c},{3,d}]).
2> S1 = sofs:set([1,2]).
3> S2 = sofs:image(R, S1).
4> sofs:to_external(S2).
[a,b,c]
```
""".
-spec(image(BinRel, Set1) -> Set2 when
      BinRel :: binary_relation(),
      Set1 :: a_set(),
      Set2 :: a_set()).
image(R, S) when ?IS_SET(R), ?IS_SET(S) ->
    case ?TYPE(R) of
        ?BINREL(DT, RT) ->
	    case match_types(DT, ?TYPE(S)) of
		true ->
		    ?SET(usort(restrict(?LIST(S), ?LIST(R))), RT);
		false ->
		    erlang:error(type_mismatch)
	    end;
        ?ANYTYPE -> R;
        _ -> erlang:error(badarg)
    end.

-doc """
Returns the [inverse image](`m:sofs#inverse_image`) of `Set1` under the binary
relation `BinRel`.

## Examples

```erlang
1> R = sofs:relation([{1,a},{2,b},{2,c},{3,d}]).
2> S1 = sofs:set([c,d,e]).
3> S2 = sofs:inverse_image(R, S1).
4> sofs:to_external(S2).
[2,3]
```
""".
-spec(inverse_image(BinRel, Set1) -> Set2 when
      BinRel :: binary_relation(),
      Set1 :: a_set(),
      Set2 :: a_set()).
inverse_image(R, S) when ?IS_SET(R), ?IS_SET(S) ->
    case ?TYPE(R) of
        ?BINREL(DT, RT) ->
	    case match_types(RT, ?TYPE(S)) of
		true ->
		    NL = restrict(?LIST(S), converse(?LIST(R), [])),
		    ?SET(usort(NL), DT);
		false ->
		    erlang:error(type_mismatch)
	    end;
        ?ANYTYPE -> R;
        _ -> erlang:error(badarg)
    end.

-doc """
Returns the [strict relation](`m:sofs#strict_relation`) corresponding to the
binary relation `BinRel1`.

## Examples

```erlang
1> R1 = sofs:relation([{1,1},{1,2},{2,1},{2,2}]).
2> R2 = sofs:strict_relation(R1).
3> sofs:to_external(R2).
[{1,2},{2,1}]
```
""".
-spec(strict_relation(BinRel1) -> BinRel2 when
      BinRel1 :: binary_relation(),
      BinRel2 :: binary_relation()).
strict_relation(R) when ?IS_SET(R) ->
    case ?TYPE(R) of
        Type = ?BINREL(_, _) ->
            ?SET(strict(?LIST(R), []), Type);
        ?ANYTYPE -> R;
        _ -> erlang:error(badarg)
    end.

-doc """
Returns a subset S of the [weak relation](`m:sofs#weak_relation`) W
corresponding to the binary relation `BinRel1`.

Let F be the [field](`m:sofs#field`) of `BinRel1`. The subset S is
defined so that x S y if x W y for some x in F and for some y in F.

## Examples

```erlang
1> R1 = sofs:relation([{1,1},{1,2},{3,1}]).
2> R2 = sofs:weak_relation(R1).
3> sofs:to_external(R2).
[{1,1},{1,2},{2,2},{3,1},{3,3}]
```
""".
-spec(weak_relation(BinRel1) -> BinRel2 when
      BinRel1 :: binary_relation(),
      BinRel2 :: binary_relation()).
weak_relation(R) when ?IS_SET(R) ->
    case ?TYPE(R) of
        ?BINREL(DT, RT) ->
            case unify_types(DT, RT) of
                [] ->
                    erlang:error(badarg);
                Type ->
                    ?SET(weak(?LIST(R)), ?BINREL(Type, Type))
            end;
        ?ANYTYPE -> R;
        _ -> erlang:error(badarg)
    end.

-doc """
Returns the [extension](`m:sofs#extension`) of `BinRel1` such that for each
element E in `Set` that does not belong to the [domain](`m:sofs#domain`) of
`BinRel1`, `BinRel2` contains the pair (E, `AnySet`).

## Examples

```erlang
1> S = sofs:set([b,c]).
2> A = sofs:empty_set().
3> R = sofs:family([{a,[1,2]},{b,[3]}]).
4> X = sofs:extension(R, S, A).
5> sofs:to_external(X).
[{a,[1,2]},{b,[3]},{c,[]}]
```
""".
-spec(extension(BinRel1, Set, AnySet) -> BinRel2 when
      AnySet :: anyset(),
      BinRel1 :: binary_relation(),
      BinRel2 :: binary_relation(),
      Set :: a_set()).
extension(R, S, E) when ?IS_SET(R), ?IS_SET(S) ->
    case {?TYPE(R), ?TYPE(S), is_sofs_set(E)} of
	{T=?BINREL(DT, RT), ST, true} ->
	    case match_types(DT, ST) andalso match_types(RT, type(E)) of
		false ->
		    erlang:error(type_mismatch);
		true ->
		    RL = ?LIST(R),
		    case extc([], ?LIST(S), to_external(E), RL) of
			[] ->
			    R;
			L ->
			    ?SET(merge(RL, reverse(L)), T)
		    end
	    end;
	{?ANYTYPE, ?ANYTYPE, true} ->
	    R;
	{?ANYTYPE, ST, true} ->
	    case type(E) of
		?SET_OF(?ANYTYPE) ->
		    R;
		ET ->
		    ?SET([], ?BINREL(ST, ET))
	    end;
	{_, _, true} ->
	    erlang:error(badarg)
    end.

-doc """
Returns `true` if the binary relation `BinRel` is a
[function](`m:sofs#function`) or the untyped empty set; otherwise,
returns `false`.

## Examples

```erlang
1> sofs:is_a_function(sofs:relation([{1,a},{2,b},{3,c}])).
true
2> sofs:is_a_function(sofs:relation([{1,a},{1,b},{3,c}])).
false
3> sofs:is_a_function(sofs:set([a,b,c])).
** exception error: bad argument
     in function  sofs:is_a_function/1
```
""".
-spec(is_a_function(BinRel) -> Bool when
      Bool :: boolean(),
      BinRel :: binary_relation()).
is_a_function(R) when ?IS_SET(R) ->
    case ?TYPE(R) of
        ?BINREL(_, _) ->
            case ?LIST(R) of
                [] -> true;
                [{V,_} | Es] -> is_a_func(Es, V)
            end;
        ?ANYTYPE -> true;
        _ -> erlang:error(badarg)
    end.

-doc """
Returns the [restriction](`m:sofs#restriction`) of the binary relation `BinRel1`
to `Set`.

## Examples

```erlang
1> R1 = sofs:relation([{1,a},{2,b},{3,c}]).
2> S = sofs:set([1,2,4]).
3> R2 = sofs:restriction(R1, S).
4> sofs:to_external(R2).
[{1,a},{2,b}]
```
""".
-spec(restriction(BinRel1, Set) -> BinRel2 when
      BinRel1 :: binary_relation(),
      BinRel2 :: binary_relation(),
      Set :: a_set()).
restriction(Relation, Set) ->
    restriction(1, Relation, Set).

-doc """
Returns the difference between the binary relation `BinRel1` and the
[restriction](`m:sofs#restriction`) of `BinRel1` to `Set`.

## Examples

```erlang
1> R1 = sofs:relation([{1,a},{2,b},{3,c}]).
2> S = sofs:set([2,4,6]).
3> R2 = sofs:drestriction(R1, S).
4> sofs:to_external(R2).
[{1,a},{3,c}]
```

[`drestriction(R, S)`](`drestriction/2`) is equivalent to
[`difference(R, restriction(R, S))`](`difference/2`).
""".
-spec(drestriction(BinRel1, Set) -> BinRel2 when
      BinRel1 :: binary_relation(),
      BinRel2 :: binary_relation(),
      Set :: a_set()).
drestriction(Relation, Set) ->
    drestriction(1, Relation, Set).

%%%
%%% Functions on functions only.
%%%

-doc """
Returns the [composite](`m:sofs#composite`) of the functions `Function1` and
`Function2`.

## Examples

```erlang
1> F1 = sofs:a_function([{a,1},{b,2},{c,2}]).
2> F2 = sofs:a_function([{1,x},{2,y},{3,z}]).
3> F = sofs:composite(F1, F2).
4> sofs:to_external(F).
[{a,x},{b,y},{c,y}]
5> sofs:composite(F2, F1).
** exception error: bad_function
     in function  sofs:composite/2
```
""".
-spec(composite(Function1, Function2) -> Function3 when
      Function1 :: a_function(),
      Function2 :: a_function(),
      Function3 :: a_function()).
composite(Fn1, Fn2) when ?IS_SET(Fn1), ?IS_SET(Fn2) ->
    ?BINREL(DTF1, RTF1) = case ?TYPE(Fn1)of
			      ?BINREL(_, _) = F1T -> F1T;
			      ?ANYTYPE -> {?ANYTYPE, ?ANYTYPE};
			      _ -> erlang:error(badarg)
			  end,
    ?BINREL(DTF2, RTF2) = case ?TYPE(Fn2) of
			      ?BINREL(_, _) = F2T -> F2T;
			      ?ANYTYPE -> {?ANYTYPE, ?ANYTYPE};
			      _ -> erlang:error(badarg)
			  end,
    case match_types(RTF1, DTF2) of
        true when DTF1 =:= ?ANYTYPE -> Fn1;
        true when DTF2 =:= ?ANYTYPE -> Fn2;
        true ->
	    case comp(?LIST(Fn1), ?LIST(Fn2)) of
		SL when is_list(SL) ->
		    ?SET(sort(SL), ?BINREL(DTF1, RTF2));
		Bad ->
		    erlang:error(Bad)
	    end;
        false -> erlang:error(type_mismatch)
    end.

-doc """
Returns the [inverse](`m:sofs#inverse`) of function `Function1`.

A `bad_function` exception is raised if `Function1` is not invertible.

See `converse/1` for a similar function that handles any binary relation.

## Examples

```erlang
1> F1 = sofs:relation([{1,a},{2,b},{3,c}]).
2> F2 = sofs:inverse(F1).
3> sofs:to_external(F2).
[{a,1},{b,2},{c,3}]
```

Trying to inverse a non-invertible function.

```erlang
1> R1 = sofs:relation([{1,a},{2,a}]).
2> sofs:inverse(R1).
** exception error: bad_function
     in function  sofs:inverse/1
3> R2 = sofs:converse(R1).
4> sofs:to_external(R2).
[{a,1},{a,2}]
```
""".
-spec(inverse(Function1) -> Function2 when
      Function1 :: a_function(),
      Function2 :: a_function()).
inverse(Fn) when ?IS_SET(Fn) ->
    case ?TYPE(Fn) of
        ?BINREL(DT, RT) ->
	    case inverse1(?LIST(Fn)) of
		SL when is_list(SL) ->
		    ?SET(SL, ?BINREL(RT, DT));
		Bad ->
		    erlang:error(Bad)
	    end;
        ?ANYTYPE -> Fn;
        _ -> erlang:error(badarg)
    end.

%%%
%%% Functions on relations (binary or other).
%%%

-doc """
Returns a subset of `Set1` containing those elements that gives an element in
`Set2` as the result of applying `SetFun`.

## Examples

```erlang
1> S1 = sofs:relation([{1,a},{2,b},{3,c}]).
2> S2 = sofs:set([b,c,d]).
3> S3 = sofs:restriction(2, S1, S2).
4> sofs:to_external(S3).
[{2,b},{3,c}]
```
""".
-spec(restriction(SetFun, Set1, Set2) -> Set3 when
      SetFun :: set_fun(),
      Set1 :: a_set(),
      Set2 :: a_set(),
      Set3 :: a_set()).
%% Equivalent to range(restriction(inverse(substitution(Fun, S1)), S2)).
restriction(I, R, S) when is_integer(I), ?IS_SET(R), ?IS_SET(S) ->
    RT = ?TYPE(R),
    ST = ?TYPE(S),
    case check_for_sort(RT, I) of
	empty ->
	    R;
	error ->
	    erlang:error(badarg);
	Sort ->
	    RL = ?LIST(R),
	    case {match_types(?REL_TYPE(I, RT), ST), ?LIST(S)} of
		{true, _SL} when RL =:= [] ->
		    R;
		{true, []} ->
                    ?SET([], RT);
		{true, [E | Es]} when Sort =:= false -> % I =:= 1
		    ?SET(reverse(restrict_n(I, RL, E, Es, [])), RT);
		{true, [E | Es]} ->
		    ?SET(sort(restrict_n(I, keysort(I, RL), E, Es, [])), RT);
		{false, _SL} ->
		    erlang:error(type_mismatch)
	    end
    end;
restriction(SetFun, S1, S2) when ?IS_SET(S1), ?IS_SET(S2) ->
    Type1 = ?TYPE(S1),
    Type2 = ?TYPE(S2),
    SL1 = ?LIST(S1),
    case external_fun(SetFun) of
	false when Type2 =:= ?ANYTYPE ->
	    S2;
	false ->
	    case subst(SL1, SetFun, element_type(Type1)) of
		{NSL, NewType} -> % NewType can be ?ANYTYPE
		    case match_types(NewType, Type2) of
			true ->
			    NL = sort(restrict(?LIST(S2), converse(NSL, []))),
			    ?SET(NL, Type1);
			false ->
			    erlang:error(type_mismatch)
		    end;
		Bad ->
		    erlang:error(Bad)
	    end;
	_ when Type1 =:= ?ANYTYPE ->
	    S1;
	_XFun when ?IS_SET_OF(Type1) ->
            erlang:error(badarg);
	XFun ->
	    FunT = XFun(Type1),
	    try check_fun(Type1, XFun, FunT) of
		Sort ->
		    case match_types(FunT, Type2) of
			true ->
			    R1 = inverse_substitution(SL1, XFun, Sort),
			    ?SET(sort(Sort, restrict(?LIST(S2), R1)), Type1);
			false ->
			    erlang:error(type_mismatch)
		    end
            catch _:_ -> erlang:error(badarg)
	    end
    end.

-doc """
Returns a subset of `Set1` containing those elements that do not give an element
in `Set2` as the result of applying `SetFun`.

## Examples

```erlang
1> SetFun = {external, fun({_A,B,C}) -> {B,C} end}.
2> R1 = sofs:relation([{a,aa,1},{b,bb,2},{c,cc,3}]).
3> R2 = sofs:relation([{bb,2},{cc,3},{dd,4}]).
4> R3 = sofs:drestriction(SetFun, R1, R2).
5> sofs:to_external(R3).
[{a,aa,1}]
```

[`drestriction(F, S1, S2)`](`drestriction/3`) is equivalent to
[`difference(S1, restriction(F, S1, S2))`](`difference/2`).
""".
-spec(drestriction(SetFun, Set1, Set2) -> Set3 when
      SetFun :: set_fun(),
      Set1 :: a_set(),
      Set2 :: a_set(),
      Set3 :: a_set()).
drestriction(I, R, S) when is_integer(I), ?IS_SET(R), ?IS_SET(S) ->
    RT = ?TYPE(R),
    ST = ?TYPE(S),
    case check_for_sort(RT, I) of
	empty ->
	    R;
	error ->
	    erlang:error(badarg);
	Sort ->
	    RL = ?LIST(R),
	    case {match_types(?REL_TYPE(I, RT), ST), ?LIST(S)} of
		{true, []} ->
		    R;
		{true, _SL} when RL =:= [] ->
		    R;
		{true, [E | Es]} when Sort =:= false -> % I =:= 1
		    ?SET(diff_restrict_n(I, RL, E, Es, []), RT);
		{true, [E | Es]} ->
		    ?SET(diff_restrict_n(I, keysort(I, RL), E, Es, []), RT);
		{false, _SL} ->
		    erlang:error(type_mismatch)
	    end
    end;
drestriction(SetFun, S1, S2) when ?IS_SET(S1), ?IS_SET(S2) ->
    Type1 = ?TYPE(S1),
    Type2 = ?TYPE(S2),
    SL1 = ?LIST(S1),
    case external_fun(SetFun) of
	false when Type2 =:= ?ANYTYPE ->
	    S1;
	false ->
	    case subst(SL1, SetFun, element_type(Type1)) of
		{NSL, NewType} -> % NewType can be ?ANYTYPE
		    case match_types(NewType, Type2) of
			true ->
			    SL2 = ?LIST(S2),
			    NL = sort(diff_restrict(SL2, converse(NSL, []))),
			    ?SET(NL, Type1);
			false ->
			    erlang:error(type_mismatch)
		    end;
		Bad ->
		    erlang:error(Bad)
	    end;
	_ when Type1 =:= ?ANYTYPE ->
	    S1;
	_XFun when ?IS_SET_OF(Type1) ->
            erlang:error(badarg);
	XFun ->
	    FunT = XFun(Type1),
	    try check_fun(Type1, XFun, FunT) of
		Sort ->
		    case match_types(FunT, Type2) of
			true ->
			    R1 = inverse_substitution(SL1, XFun, Sort),
			    SL2 = ?LIST(S2),
			    ?SET(sort(Sort, diff_restrict(SL2, R1)), Type1);
			false ->
			    erlang:error(type_mismatch)
		    end
            catch _:_ -> erlang:error(badarg)
	    end
    end.

-doc """
Returns the set created by substituting each element of `Set1` by the result of
applying `SetFun` to the element.

If `SetFun` is a number i >= 1 and `Set1` is a relation, then the returned set
is the [projection](`m:sofs#projection`) of `Set1` onto coordinate i.

## Examples

```erlang
1> S1 = sofs:from_term([{1,a},{2,b},{3,a}]).
2> S2 = sofs:projection(2, S1).
3> sofs:to_external(S2).
[a,b]
```

Projecting using an external SetFun.

```erlang
1> S1 = sofs:relation([{1,2,7}, {4,3,2}]).
2> SetFun = {external,fun({X,_,Z}) -> {X,Z} end}.
3> S2 = sofs:projection(SetFun, S1).
4> sofs:to_external(S2).
[{1,7},{4,2}]
```
""".
-spec(projection(SetFun, Set1) -> Set2 when
      SetFun :: set_fun(),
      Set1 :: a_set(),
      Set2 :: a_set()).
projection(I, Set) when is_integer(I), ?IS_SET(Set) ->
    Type = ?TYPE(Set),
    case check_for_sort(Type, I) of
        empty ->
            Set;
        error ->
            erlang:error(badarg);
	_ when I =:= 1 ->
	    ?SET(projection1(?LIST(Set)), ?REL_TYPE(I, Type));
        _ ->
	    ?SET(projection_n(?LIST(Set), I, []), ?REL_TYPE(I, Type))
    end;
projection(Fun, Set) ->
    range(substitution(Fun, Set)).

-doc """
Returns a function with the domain `Set1`, where each element maps to
the result of applying `SetFun` to it.

## Examples

```erlang
1> R = sofs:relation([{a,1},{b,2}]).
2> sofs:to_external(sofs:projection(1, R)).
[a,b]
3> sofs:to_external(sofs:substitution(1, R)).
[{{a,1},a},{{b,2},b}]
4> SetFun = {external, fun({A,_}=E) -> {E,A} end}.
5> sofs:to_external(sofs:projection(SetFun, R)).
[{{a,1},a},{{b,2},b}]
```

The relation of equality between the elements of {a,b,c}:

```erlang
1> I = sofs:substitution(fun(A) -> A end, sofs:set([a,b,c])).
2> sofs:to_external(I).
[{a,a},{b,b},{c,c}]
```

Let `SetOfSets` be a set of sets and `BinRel` a binary relation. The function
that maps each element `Set` of `SetOfSets` onto the [image](`m:sofs#image`) of
`Set` under `BinRel` is returned by the `Images` fun in the following example.

```erlang
1> Images = fun(SetOfSets, BinRel) ->
                    Fun = fun(Set) -> sofs:image(BinRel, Set) end,
                    sofs:substitution(Fun, SetOfSets)
            end.
2> S1 = sofs:set([1,2]).
3> S2 = sofs:set([1,3,4]).
4> S3 = sofs:set([x]).
5> SetsOfSets = sofs:from_sets([S1,S2,S3]).
6> BinRel = sofs:relation([{1,a}, {2,b}, {3,c}, {4,d}]).
7> S4 = Images(SetsOfSets, BinRel).
8> sofs:to_external(S4).
[{[1,2],[a,b]},{[1,3,4],[a,c,d]},{[x],[]}]
```

External unordered sets are represented as sorted lists. So, creating
the image of a set under a relation R can traverse all elements of R
(to that comes the sorting of results, the image). In the `Image` fun,
`BinRel` is traversed once for each element of `SetOfSets`.

The following `Images2` fun is more efficient. It can can be used
under the assumption that the image of each element of `SetOfSets`
under `BinRel` is non-empty.

```erlang
1> Images2 = fun(SetOfSets, BinRel) ->
                 CR = sofs:canonical_relation(SetOfSets),
                 R = sofs:relative_product1(CR, BinRel),
                 sofs:relation_to_family(R)
   end.
2> S1 = sofs:set([1,2]).
3> S2 = sofs:set([1,3,4]).
4> S3 = sofs:set([x]).
5> SetsOfSets = sofs:from_sets([S1,S2,S3]).
6> BinRel = sofs:relation([{1,a}, {2,b}, {3,c}, {4,d}]).
7> S4 = Images2(SetsOfSets, BinRel).
8> sofs:to_external(S4).
[{[1,2],[a,b]},{[1,3,4],[a,c,d]}]
```

Note that `S3`, which has an empty image, is missing from the result.
""".
-spec(substitution(SetFun, Set1) -> Set2 when
      SetFun :: set_fun(),
      Set1 :: a_set(),
      Set2 :: a_set()).
substitution(I, Set) when is_integer(I), ?IS_SET(Set) ->
    Type = ?TYPE(Set),
    case check_for_sort(Type, I) of
	empty ->
	    Set;
	error ->
	    erlang:error(badarg);
	_Sort ->
	    NType = ?REL_TYPE(I, Type),
	    NSL = substitute_element(?LIST(Set), I, []),
	    ?SET(NSL, ?BINREL(Type, NType))
    end;
substitution(SetFun, Set) when ?IS_SET(Set) ->
    Type = ?TYPE(Set),
    L = ?LIST(Set),
    case external_fun(SetFun) of
	false when L =/= [] ->
	    case subst(L, SetFun, element_type(Type)) of
		{SL, NewType} ->
		    ?SET(reverse(SL), ?BINREL(Type, NewType));
		Bad ->
		    erlang:error(Bad)
	    end;
	false ->
	    empty_set();
	_ when Type =:= ?ANYTYPE ->
	    empty_set();
	_XFun when ?IS_SET_OF(Type) ->
            erlang:error(badarg);
	XFun ->
	    FunT = XFun(Type),
	    try check_fun(Type, XFun, FunT) of
		_Sort ->
		    SL = substitute(L, XFun, []),
		    ?SET(SL, ?BINREL(Type, FunT))
            catch _:_ -> erlang:error(badarg)
	    end
    end.

-doc """
Returns the [partition](`m:sofs#partition`) of the union of the set of sets
`SetOfSets` such that two elements are considered equal if they belong to the
same elements of `SetOfSets`.

## Examples

```erlang
1> Sets1 = sofs:from_term([[a,b,c],[d,e,f],[g,h,i]]).
2> Sets2 = sofs:from_term([[b,c,d],[e,f,g],[h,i,j]]).
3> P = sofs:partition(sofs:union(Sets1, Sets2)).
4> sofs:to_external(P).
[[a],[b,c],[d],[e,f],[g],[h,i],[j]]
```
""".
-spec(partition(SetOfSets) -> Partition when
      SetOfSets :: set_of_sets(),
      Partition :: a_set()).
partition(Sets) ->
    F1 = relation_to_family(canonical_relation(Sets)),
    F2 = relation_to_family(converse(F1)),
    range(F2).

-doc """
Returns the [partition](`m:sofs#partition`) of `Set` such that two elements are
considered equal if the results of applying `SetFun` are equal.

## Examples

```erlang
1> Ss = sofs:from_term([[a],[b],[c,d],[e,f]]).
2> SetFun = fun(S) -> sofs:from_term(sofs:no_elements(S)) end.
3> P = sofs:partition(SetFun, Ss).
4> sofs:to_external(P).
[[[a],[b]],[[c,d],[e,f]]]
```
""".
-spec(partition(SetFun, Set) -> Partition when
      SetFun :: set_fun(),
      Partition :: a_set(),
      Set :: a_set()).
partition(I, Set) when is_integer(I), ?IS_SET(Set) ->
    Type = ?TYPE(Set),
    case check_for_sort(Type, I) of
        empty ->
            Set;
        error ->
            erlang:error(badarg);
	false -> % I =:= 1
	    ?SET(partition_n(I, ?LIST(Set)), ?SET_OF(Type));
        true ->
	    ?SET(partition_n(I, keysort(I, ?LIST(Set))), ?SET_OF(Type))
    end;
partition(Fun, Set) ->
    range(partition_family(Fun, Set)).

-doc """
Returns a pair of sets that, regarded as constituting a set, forms a
[partition](`m:sofs#partition`) of `Set1`.

If the result of applying `SetFun` to an element of `Set1` gives an
element in `Set2`, the element belongs to `Set3`, otherwise the
element belongs to `Set4`.

[`partition(F, S1, S2)`](`partition/3`) is equivalent to
`{restriction(F, S1, S2), drestriction(F, S1, S2)}`.

## Examples

```erlang
1> R1 = sofs:relation([{1,a},{2,b},{3,c}]).
2> S = sofs:set([2,4,6]).
3> {R2,R3} = sofs:partition(1, R1, S).
4> {sofs:to_external(R2),sofs:to_external(R3)}.
{[{2,b}],[{1,a},{3,c}]}
```
""".
-spec(partition(SetFun, Set1, Set2) -> {Set3, Set4} when
      SetFun :: set_fun(),
      Set1 :: a_set(),
      Set2 :: a_set(),
      Set3 :: a_set(),
      Set4 :: a_set()).
partition(I, R, S) when is_integer(I), ?IS_SET(R), ?IS_SET(S) ->
    RT = ?TYPE(R),
    ST = ?TYPE(S),
    case check_for_sort(RT, I) of
	empty ->
	    {R, R};
	error ->
	    erlang:error(badarg);
	Sort ->
	    RL = ?LIST(R),
	    case {match_types(?REL_TYPE(I, RT), ST), ?LIST(S)} of
		{true, _SL} when RL =:= [] ->
		    {R, R};
		{true, []} ->
		    {?SET([], RT), R};
		{true, [E | Es]} when Sort =:= false -> % I =:= 1
		    [L1 | L2] = partition3_n(I, RL, E, Es, [], []),
		    {?SET(L1, RT), ?SET(L2, RT)};
		{true, [E | Es]} ->
		    [L1 | L2] = partition3_n(I, keysort(I,RL), E, Es, [], []),
		    {?SET(L1, RT), ?SET(L2, RT)};
		{false, _SL} ->
		    erlang:error(type_mismatch)
	    end
    end;
partition(SetFun, S1, S2) when ?IS_SET(S1), ?IS_SET(S2) ->
    Type1 = ?TYPE(S1),
    Type2 = ?TYPE(S2),
    SL1 = ?LIST(S1),
    case external_fun(SetFun) of
	false when Type2 =:= ?ANYTYPE ->
	    {S2, S1};
	false ->
	    case subst(SL1, SetFun, element_type(Type1)) of
		{NSL, NewType} -> % NewType can be ?ANYTYPE
		    case match_types(NewType, Type2) of
			true ->
			    R1 = converse(NSL, []),
			    [L1 | L2] = partition3(?LIST(S2), R1),
			    {?SET(sort(L1), Type1), ?SET(sort(L2), Type1)};
			false ->
			    erlang:error(type_mismatch)
		    end;
		Bad ->
		    erlang:error(Bad)
	    end;
	_ when Type1 =:= ?ANYTYPE ->
	    {S1, S1};
	_XFun when ?IS_SET_OF(Type1) ->
            erlang:error(badarg);
	XFun ->
	    FunT = XFun(Type1),
	    try check_fun(Type1, XFun, FunT) of
		Sort ->
		    case match_types(FunT, Type2) of
			true ->
			    R1 = inverse_substitution(SL1, XFun, Sort),
			    [L1 | L2] = partition3(?LIST(S2), R1),
			    {?SET(sort(L1), Type1), ?SET(sort(L2), Type1)};
			false ->
			    erlang:error(type_mismatch)
		    end
            catch _:_ -> erlang:error(badarg)
	    end
    end.

-doc """
If `TupleOfBinRels` is a non-empty tuple \{R\[1], ..., R\[n]\} of binary
relations and `BinRel1` is a binary relation, then `BinRel2` is the
[multiple relative product](`m:sofs#multiple_relative_product`) of the ordered
set (R\[i], ..., R\[n]) and `BinRel1`.

## Examples

```erlang
1> Ri = sofs:relation([{a,1},{b,2},{c,3}]).
2> R = sofs:relation([{a,b},{b,c},{c,a}]).
3> MP = sofs:multiple_relative_product({Ri, Ri}, R).
4> sofs:to_external(sofs:range(MP)).
[{1,2},{2,3},{3,1}]
```
""".
-spec(multiple_relative_product(TupleOfBinRels, BinRel1) -> BinRel2 when
      TupleOfBinRels :: tuple_of(BinRel),
      BinRel :: binary_relation(),
      BinRel1 :: binary_relation(),
      BinRel2 :: binary_relation()).
multiple_relative_product(T, R) when is_tuple(T), ?IS_SET(R) ->
    case test_rel(R, tuple_size(T), eq) of
	true when ?TYPE(R) =:= ?ANYTYPE ->
	    empty_set();
        true ->
	    MProd = mul_relprod(tuple_to_list(T), 1, R),
	    relative_product(MProd);
        false ->
	    erlang:error(badarg)
    end.

-doc """
Returns the [natural join](`m:sofs#natural_join`) of the relations `Relation1`
and `Relation2` on coordinates `I` and `J`.

## Examples

```erlang
1> R1 = sofs:relation([{a,x,1},{b,y,2}]).
2> R2 = sofs:relation([{1,f,g},{1,h,i},{2,3,4}]).
3> J = sofs:join(R1, 3, R2, 1).
4> sofs:to_external(J).
[{a,x,1,f,g},{a,x,1,h,i},{b,y,2,3,4}]
```
""".
-spec(join(Relation1, I, Relation2, J) -> Relation3 when
      Relation1 :: relation(),
      Relation2 :: relation(),
      Relation3 :: relation(),
      I :: pos_integer(),
      J :: pos_integer()).
join(R1, I1, R2, I2)
  when ?IS_SET(R1), ?IS_SET(R2), is_integer(I1), is_integer(I2) ->
    case test_rel(R1, I1, lte) andalso test_rel(R2, I2, lte) of
        false -> erlang:error(badarg);
        true when ?TYPE(R1) =:= ?ANYTYPE -> R1;
        true when ?TYPE(R2) =:= ?ANYTYPE -> R2;
        true ->
	    L1 = ?LIST(raise_element(R1, I1)),
	    L2 = ?LIST(raise_element(R2, I2)),
	    T = relprod1(L1, L2),
	    F = case I1 =:= 1 andalso I2 =:= 1 of
		    true ->
			fun({X,Y}) -> join_element(X, Y) end;
		    false ->
			fun({X,Y}) ->
				list_to_tuple(join_element(X, Y, I2))
			end
		end,
	    ?SET(replace(T, F, []), F({?TYPE(R1), ?TYPE(R2)}))
    end.

%% Inlined.
test_rel(R, I, C) ->
    case ?TYPE(R) of
        Rel when ?IS_RELATION(Rel), C =:= eq, I =:= ?REL_ARITY(Rel) -> true;
        Rel when ?IS_RELATION(Rel), C =:= lte, I>=1, I =< ?REL_ARITY(Rel) ->
            true;
        ?ANYTYPE -> true;
        _ -> false
    end.

%%%
%%% Family functions
%%%

-doc false.
-spec(fam2rel(Family) -> BinRel when
      Family :: family(),
      BinRel :: binary_relation()).
fam2rel(F) ->
    family_to_relation(F).

-doc """
If `Family` is a [family](`m:sofs#family`), then `BinRel` is the binary relation
containing all pairs (i, x) such that i belongs to the index set of `Family` and
x belongs to `Family`\[i].

## Examples

```erlang
1> F = sofs:family([{a,[]}, {b,[1]}, {c,[2,3]}]).
2> R = sofs:family_to_relation(F).
3> sofs:to_external(R).
[{b,1},{c,2},{c,3}]
```
""".
-spec(family_to_relation(Family) -> BinRel when
      Family :: family(),
      BinRel :: binary_relation()).
%% Inlined.
family_to_relation(F) when ?IS_SET(F) ->
    case ?TYPE(F) of
        ?FAMILY(DT, RT) ->
	    ?SET(family2rel(?LIST(F), []), ?BINREL(DT, RT));
        ?ANYTYPE -> F;
        _ -> erlang:error(badarg)
    end.

-doc """
If `Family1` is a [family](`m:sofs#family`), then `Family2` is the
[restriction](`m:sofs#restriction`) of `Family1` to those elements i of the
index set for which `Fun` applied to `Family1`\[i] returns `true`.

If `Fun` is a tuple `{external, Fun2}`, then `Fun2` is applied to the
[external set](`m:sofs#external_set`) of `Family1`\[i]; otherwise
`Fun` is applied to `Family1`\[i].

## Examples

```erlang
1> F1 = sofs:family([{a,[1,2,3]},{b,[1,2]},{c,[1]}]).
2> SpecFun = fun(S) -> sofs:no_elements(S) =:= 2 end.
3> F2 = sofs:family_specification(SpecFun, F1).
4> sofs:to_external(F2).
[{b,[1,2]}]
```
""".
-spec(family_specification(Fun, Family1) -> Family2 when
      Fun :: spec_fun(),
      Family1 :: family(),
      Family2 :: family()).
family_specification(Fun, F) when ?IS_SET(F) ->
    case ?TYPE(F) of
        ?FAMILY(_DT, Type) = FType ->
	    R = case external_fun(Fun) of
		    false ->
			fam_spec(?LIST(F), Fun, Type, []);
		    XFun ->
			fam_specification(?LIST(F), XFun, [])
		end,
	    case R of
		SL when is_list(SL) ->
		    ?SET(SL, FType);
		Bad ->
		    erlang:error(Bad)
	    end;
        ?ANYTYPE -> F;
        _ -> erlang:error(badarg)
    end.

-doc """
Returns the union of [family](`m:sofs#family`) `Family`.

## Examples

```erlang
1> F = sofs:family([{a,[0,2,4]},{b,[0,1,2]},{c,[2,3]}]).
2> S = sofs:union_of_family(F).
3> sofs:to_external(S).
[0,1,2,3,4]
```
""".
-spec(union_of_family(Family) -> Set when
      Family :: family(),
      Set :: a_set()).
union_of_family(F) when ?IS_SET(F) ->
    case ?TYPE(F) of
        ?FAMILY(_DT, Type) ->
	    ?SET(un_of_fam(?LIST(F), []), Type);
        ?ANYTYPE -> F;
        _ -> erlang:error(badarg)
    end.

-doc """
Returns the intersection of [family](`m:sofs#family`) `Family`.

Intersecting an empty family exits the process with a `badarg` message.

## Examples

```erlang
1> F = sofs:family([{a,[0,2,4]},{b,[0,1,2]},{c,[2,3]}]).
2> S = sofs:intersection_of_family(F).
3> sofs:to_external(S).
[2]
```
""".
-spec(intersection_of_family(Family) -> Set when
      Family :: family(),
      Set :: a_set()).
intersection_of_family(F) when ?IS_SET(F) ->
    case ?TYPE(F) of
        ?FAMILY(_DT, Type) ->
            case int_of_fam(?LIST(F)) of
                FU when is_list(FU) ->
                    ?SET(FU, Type);
                Bad ->
                    erlang:error(Bad)
            end;
        _ -> erlang:error(badarg)
    end.

-doc """
If `Family1` is a [family](`m:sofs#family`) and `Family1`\[i] is a set of sets
for each i in the index set of `Family1`, then `Family2` is the family with the
same index set as `Family1` such that `Family2`\[i] is the
[union](`m:sofs#union_n`) of `Family1`\[i].

## Examples

```erlang
1> F1 = sofs:from_term([{a,[[1,2],[2,3]]},{b,[[]]}]).
2> F2 = sofs:family_union(F1).
3> sofs:to_external(F2).
[{a,[1,2,3]},{b,[]}]
```

[`family_union(F)`](`family_union/1`) is equivalent to
[`family_projection(fun sofs:union/1, F)`](`family_projection/2`).
""".
-spec(family_union(Family1) -> Family2 when
      Family1 :: family(),
      Family2 :: family()).
family_union(F) when ?IS_SET(F) ->
    case ?TYPE(F) of
        ?FAMILY(DT, ?SET_OF(Type)) ->
	    ?SET(fam_un(?LIST(F), []), ?FAMILY(DT, Type));
        ?ANYTYPE -> F;
        _ -> erlang:error(badarg)
    end.

-doc """
If `Family1` is a [family](`m:sofs#family`) and `Family1`[i] is a set of sets
for every i in the index set of `Family1`, then `Family2` is the family with the
same index set as `Family1` such that `Family2`[i] is the
[intersection](`m:sofs#intersection_n`) of `Family1`[i].

If `Family1`[i] is an empty set for some i, a `badarg` exception is raised.

## Examples

```erlang
1> F1 = sofs:from_term([{a,[[1,2,3],[2,3,4]]},{b,[[x,y,z],[x,y]]}]).
2> F2 = sofs:family_intersection(F1).
3> sofs:to_external(F2).
[{a,[2,3]},{b,[x,y]}]
4> F3 = sofs:from_term([{a,[[1,2]]},{b,[]}]).
5> sofs:family_intersection(F3).
** exception error: bad argument
     in function  sofs:family_intersection/1
```
""".
-spec(family_intersection(Family1) -> Family2 when
      Family1 :: family(),
      Family2 :: family()).
family_intersection(F) when ?IS_SET(F) ->
    case ?TYPE(F) of
        ?FAMILY(DT, ?SET_OF(Type)) ->
            case fam_int(?LIST(F), []) of
                FU when is_list(FU) ->
                    ?SET(FU, ?FAMILY(DT, Type));
                Bad ->
                    erlang:error(Bad)
            end;
        ?ANYTYPE -> F;
        _ -> erlang:error(badarg)
    end.

-doc """
If `Family1` is a [family](`m:sofs#family`) and `Family1`\[i] is a binary
relation for every i in the index set of `Family1`, then `Family2` is the family
with the same index set as `Family1` such that `Family2`\[i] is the
[domain](`m:sofs#domain`) of `Family1[i]`.

## Examples

```erlang
1> FR = sofs:from_term([{a,[{1,a},{2,b},{3,c}]},{b,[]},{c,[{4,d},{5,e}]}]).
2> F = sofs:family_domain(FR).
3> sofs:to_external(F).
[{a,[1,2,3]},{b,[]},{c,[4,5]}]
```
""".
-spec(family_domain(Family1) -> Family2 when
      Family1 :: family(),
      Family2 :: family()).
family_domain(F) when ?IS_SET(F) ->
    case ?TYPE(F) of
        ?FAMILY(FDT, ?BINREL(DT, _)) ->
            ?SET(fam_dom(?LIST(F), []), ?FAMILY(FDT, DT));
        ?ANYTYPE -> F;
        ?FAMILY(_, ?ANYTYPE) -> F;
        _ -> erlang:error(badarg)
    end.

-doc """
If `Family1` is a [family](`m:sofs#family`) and `Family1`\[i] is a binary
relation for every i in the index set of `Family1`, then `Family2` is the family
with the same index set as `Family1` such that `Family2`\[i] is the
[range](`m:sofs#range`) of `Family1`\[i].

## Examples

```erlang
1> FR = sofs:from_term([{a,[{1,a},{2,b},{3,c}]},{b,[]},{c,[{4,d},{5,e}]}]).
2> F = sofs:family_range(FR).
3> sofs:to_external(F).
[{a,[a,b,c]},{b,[]},{c,[d,e]}]
```
""".
-spec(family_range(Family1) -> Family2 when
      Family1 :: family(),
      Family2 :: family()).
family_range(F) when ?IS_SET(F) ->
    case ?TYPE(F) of
        ?FAMILY(DT, ?BINREL(_, RT)) ->
            ?SET(fam_ran(?LIST(F), []), ?FAMILY(DT, RT));
        ?ANYTYPE -> F;
        ?FAMILY(_, ?ANYTYPE) -> F;
        _ -> erlang:error(badarg)
    end.

-doc """
If `Family1` is a [family](`m:sofs#family`) and `Family1`\[i] is a binary
relation for every i in the index set of `Family1`, then `Family2` is the family
with the same index set as `Family1` such that `Family2`\[i] is the
[field](`m:sofs#field`) of `Family1`\[i].

## Examples

```erlang
1> FR = sofs:from_term([{a,[{1,a},{2,b},{3,c}]},{b,[]},{c,[{4,d},{5,e}]}]).
2> F = sofs:family_field(FR).
3> sofs:to_external(F).
[{a,[1,2,3,a,b,c]},{b,[]},{c,[4,5,d,e]}]
```

[`family_field(Family1)`](`family_field/1`) is equivalent to
[`family_union(family_domain(Family1), family_range(Family1))`](`family_union/2`).
""".
-spec(family_field(Family1) -> Family2 when
      Family1 :: family(),
      Family2 :: family()).
family_field(F) ->
    family_union(family_domain(F), family_range(F)).

-doc """
If `Family1` and `Family2` are [families](`m:sofs#family`), then `Family3` is
the family such that the index set is the union of `Family1`:s and `Family2`:s
index sets, and `Family3`\[i] is the union of `Family1`\[i] and `Family2`\[i] if
both map i, otherwise `Family1`\[i] or `Family2`\[i].

## Examples

```erlang
1> F1 = sofs:family([{a,[1,2]},{b,[3,4]},{c,[5,6]}]).
2> F2 = sofs:family([{b,[4,5]},{c,[7,8]},{d,[9,10]}]).
3> F3 = sofs:family_union(F1, F2).
4> sofs:to_external(F3).
[{a,[1,2]},{b,[3,4,5]},{c,[5,6,7,8]},{d,[9,10]}]
```
""".
-spec(family_union(Family1, Family2) -> Family3 when
      Family1 :: family(),
      Family2 :: family(),
      Family3 :: family()).
family_union(F1, F2) ->
    fam_binop(F1, F2, fun fam_union/3).

-doc """
If `Family1` and `Family2` are [families](`m:sofs#family`), then `Family3` is
the family such that the index set is the intersection of `Family1`:s and
`Family2`:s index sets, and `Family3`\[i] is the intersection of `Family1`\[i]
and `Family2`\[i].

## Examples

```erlang
1> F1 = sofs:family([{a,[1,2]},{b,[3,4]},{c,[5,6]}]).
2> F2 = sofs:family([{b,[4,5]},{c,[7,8]},{d,[9,10]}]).
3> F3 = sofs:family_intersection(F1, F2).
4> sofs:to_external(F3).
[{b,[4]},{c,[]}]
```
""".
-spec(family_intersection(Family1, Family2) -> Family3 when
      Family1 :: family(),
      Family2 :: family(),
      Family3 :: family()).
family_intersection(F1, F2) ->
    fam_binop(F1, F2, fun fam_intersect/3).

-doc """
If `Family1` and `Family2` are [families](`m:sofs#family`), then `Family3` is
the family such that the index set is equal to the index set of `Family1`, and
`Family3`\[i] is the difference between `Family1`\[i] and `Family2`\[i] if
`Family2` maps i, otherwise `Family1[i]`.

## Examples

```erlang
1> F1 = sofs:family([{a,[1,2]},{b,[3,4]}]).
2> F2 = sofs:family([{b,[4,5]},{c,[6,7]}]).
3> F3 = sofs:family_difference(F1, F2).
4> sofs:to_external(F3).
[{a,[1,2]},{b,[3]}]
```
""".
-spec(family_difference(Family1, Family2) -> Family3 when
      Family1 :: family(),
      Family2 :: family(),
      Family3 :: family()).
family_difference(F1, F2) ->
    fam_binop(F1, F2, fun fam_difference/3).

%% Inlined.
fam_binop(F1, F2, FF) when ?IS_SET(F1), ?IS_SET(F2) ->
    case unify_types(?TYPE(F1), ?TYPE(F2)) of
        [] ->
            erlang:error(type_mismatch);
        ?ANYTYPE ->
            F1;
        Type = ?FAMILY(_, _) ->
	    ?SET(FF(?LIST(F1), ?LIST(F2), []), Type);
        _ ->  erlang:error(badarg)
    end.

-doc """
Returns [family](`m:sofs#family`) `Family` where the indexed set is a
[partition](`m:sofs#partition`) of `Set` such that two elements are considered
equal if the results of applying `SetFun` are the same value i.

This is the index that `Family` maps onto the [equivalence
class](`m:sofs#equivalence_class`).

## Examples

```erlang
1> S = sofs:relation([{a,a,a,a},{a,a,b,b},{a,b,b,b}]).
2> SetFun = {external, fun({A,_,C,_}) -> {A,C} end}.
3> F = sofs:partition_family(SetFun, S).
4> sofs:to_external(F).
[{{a,a},[{a,a,a,a}]},{{a,b},[{a,a,b,b},{a,b,b,b}]}]
```
""".
-spec(partition_family(SetFun, Set) -> Family when
      Family :: family(),
      SetFun :: set_fun(),
      Set :: a_set()).
partition_family(I, Set) when is_integer(I), ?IS_SET(Set) ->
    Type = ?TYPE(Set),
    case check_for_sort(Type, I) of
        empty ->
            Set;
        error ->
            erlang:error(badarg);
	false -> % when I =:= 1
	    ?SET(fam_partition_n(I, ?LIST(Set)),
		 ?BINREL(?REL_TYPE(I, Type), ?SET_OF(Type)));
        true ->
	    ?SET(fam_partition_n(I, keysort(I, ?LIST(Set))),
		 ?BINREL(?REL_TYPE(I, Type), ?SET_OF(Type)))
    end;
partition_family(SetFun, Set) when ?IS_SET(Set) ->
    Type = ?TYPE(Set),
    SL = ?LIST(Set),
    case external_fun(SetFun) of
	false when SL =/= [] ->
	    case subst(SL, SetFun, element_type(Type)) of
		{NSL, NewType} ->
		    P = fam_partition(converse(NSL, []), true),
		    ?SET(reverse(P), ?BINREL(NewType, ?SET_OF(Type)));
		Bad ->
		    erlang:error(Bad)
	    end;
	false ->
	    empty_set();
	_ when Type =:= ?ANYTYPE ->
	    empty_set();
	_XFun when ?IS_SET_OF(Type) ->
            erlang:error(badarg);
	XFun ->
	    DType = XFun(Type),
	    try check_fun(Type, XFun, DType) of
		Sort ->
		    Ts = inverse_substitution(?LIST(Set), XFun, Sort),
		    P = fam_partition(Ts, Sort),
		    ?SET(reverse(P), ?BINREL(DType, ?SET_OF(Type)))
            catch _:_ -> erlang:error(badarg)
	    end
    end.

-doc """
If `Family1` is a [family](`m:sofs#family`), then `Family2` is the family with
the same index set as `Family1` such that `Family2`\[i] is the result of calling
`SetFun` with `Family1`\[i] as argument.

## Examples

```erlang
1> F1 = sofs:from_term([{a,[[1,2],[2,3]]},{b,[[]]}]).
2> F2 = sofs:family_projection(fun sofs:union/1, F1).
3> sofs:to_external(F2).
[{a,[1,2,3]},{b,[]}]
```
""".
-spec(family_projection(SetFun, Family1) -> Family2 when
      SetFun :: set_fun(),
      Family1 :: family(),
      Family2 :: family()).
family_projection(SetFun, F) when ?IS_SET(F) ->
    case ?TYPE(F) of
        ?FAMILY(_, _) when [] =:= ?LIST(F) ->
	    empty_set();
        ?FAMILY(DT, Type) ->
	    case external_fun(SetFun) of
		false ->
		    case fam_proj(?LIST(F), SetFun, Type, ?ANYTYPE, []) of
			{SL, NewType} ->
			    ?SET(SL, ?BINREL(DT, NewType));
			Bad ->
			    erlang:error(Bad)
		    end;
		_ ->
		    erlang:error(badarg)
	    end;
	?ANYTYPE -> F;
        _ -> erlang:error(badarg)
    end.

%%%
%%% Digraph functions
%%%

-doc(#{equiv => family_to_digraph(Family, [])}).
-spec(family_to_digraph(Family) -> Graph when
      Graph :: digraph:graph(),
      Family :: family()).
family_to_digraph(F) when ?IS_SET(F) ->
    case ?TYPE(F) of
        ?FAMILY(_, _) -> fam2digraph(F, digraph:new());
        ?ANYTYPE -> digraph:new();
        _Else -> erlang:error(badarg)
    end.

-doc """
Creates a directed graph from [family](`m:sofs#family`) `Family`.

For each pair (a, \{b\[1], ..., b\[n]\}) of `Family`, vertex a and the
edges (a, b\[i]) for 1 <= i <= n are added to a newly created directed
graph.

`GraphType` is passed on to `digraph:new/1`.

It F is a family, it holds that F is a subset of
[`digraph_to_family(family_to_digraph(F), type(F))`](`digraph_to_family/2`).
Equality holds if [`union_of_family(F)`](`union_of_family/1`) is a subset of
[`domain(F)`](`domain/1`).

Creating a cycle in an acyclic graph exits the process with a `cyclic` message.

## Examples

```erlang
1> F1 = sofs:family([{1,[a,b]}, {2,[c,d]}, {3,[d]}, {a,[b]}]).
2> G = sofs:family_to_digraph(F1, []).
3> digraph_utils:topsort(G).
[1,a,b,2,c,3,d]
4> F2 = sofs:family([{1,[1]}]).
5> sofs:family_to_digraph(F2, [acyclic]).
** exception error: cyclic
     in function  sofs:family_to_digraph/2
```
""".
-spec(family_to_digraph(Family, GraphType) -> Graph when
      Graph :: digraph:graph(),
      Family :: family(),
      GraphType :: [digraph:d_type()]).
family_to_digraph(F, Type) when ?IS_SET(F) ->
    case ?TYPE(F) of
        ?FAMILY(_, _) -> ok;
        ?ANYTYPE -> ok;
        _Else  -> erlang:error(badarg)
    end,
    try digraph:new(Type) of
        G ->
            try
                fam2digraph(F, G)
            catch
                throw:{error, Reason} ->
                    true = digraph:delete(G),
                    erlang:error(Reason)
            end
    catch
        error:badarg -> erlang:error(badarg)
    end.

-doc(#{equiv => digraph_to_family(Graph, [{atom, [atom]}])}).
-spec(digraph_to_family(Graph) -> Family when
      Graph :: digraph:graph(),
      Family :: family()).
digraph_to_family(G) ->
    try digraph_family(G) of
        L -> ?SET(L, ?FAMILY(?ATOM_TYPE, ?ATOM_TYPE))
    catch _:_ -> erlang:error(badarg)
    end.

-doc """
Creates a [family](`m:sofs#family`) from the directed graph `Graph`.

Each vertex a of `Graph` is represented by a pair
(a, \{b\[1], ..., b\[n]\}), where the b\[i]:s are the out-neighbors of
a. It is assumed that `Type` is a [valid type](`m:sofs#valid_type`) of
the external set of the family.

If G is a directed graph, it holds that the vertices and edges of G
are the same as the vertices and edges of
[`family_to_digraph(digraph_to_family(G))`](`family_to_digraph/1`).

## Examples

```erlang
1> G = digraph:new().
2> digraph:add_vertex(G, 1).
3> digraph:add_vertex(G, a).
4> digraph:add_vertex(G, b).
5> digraph:add_edge(G, 1, a).
6> digraph:add_edge(G, 1, b).
7> F = sofs:digraph_to_family(G).
8> sofs:to_external(F).
[{1,[a,b]},{a,[]},{b,[]}]
```
""".
-spec(digraph_to_family(Graph, Type) -> Family when
      Graph :: digraph:graph(),
      Family :: family(),
      Type :: type()).
digraph_to_family(G, T) ->
    case {is_type(T), T} of
        {true, ?SET_OF(?FAMILY(_,_) = Type)} ->
            try digraph_family(G) of
                L -> ?SET(L, Type)
            catch _:_ -> erlang:error(badarg)
            end;
        _ ->
            erlang:error(badarg)
    end.

%%
%%  Local functions
%%

%% Type = OrderedSetType
%%      | SetType
%%      | atom() except '_'
%% OrderedSetType = {Type, ..., Type}
%% SetType = [ElementType]           % list of exactly one element
%% ElementType = '_'                 % any type (implies empty set)
%%             | Type

is_types(0, _T) ->
    true;
is_types(I, T) ->
    case is_type(?REL_TYPE(I, T)) of
        true -> is_types(I-1, T);
        false -> false
    end.

is_element_type(?ANYTYPE) ->
    true;
is_element_type(T) ->
    is_type(T).

set_of_sets([S | Ss], L, T0) when ?IS_SET(S) ->
    case unify_types([?TYPE(S)], T0) of
        [] -> {error, type_mismatch};
        Type ->  set_of_sets(Ss, [?LIST(S) | L], Type)
    end;
set_of_sets([S | Ss], L, T0) when ?IS_ORDSET(S) ->
    case unify_types(?ORDTYPE(S), T0) of
        [] -> {error, type_mismatch};
        Type ->  set_of_sets(Ss, [?ORDDATA(S) | L], Type)
    end;
set_of_sets([], L, T) ->
    ?SET(usort(L), T);
set_of_sets(_, _L, _T) ->
    {error, badarg}.

ordset_of_sets([S | Ss], L, T) when ?IS_SET(S) ->
    ordset_of_sets(Ss, [?LIST(S) | L], [[?TYPE(S)] | T]);
ordset_of_sets([S | Ss], L, T) when ?IS_ORDSET(S) ->
    ordset_of_sets(Ss, [?ORDDATA(S) | L], [?ORDTYPE(S) | T]);
ordset_of_sets([], L, T) ->
    ?ORDSET(list_to_tuple(reverse(L)), list_to_tuple(reverse(T)));
ordset_of_sets(_, _L, _T) ->
    error.

%% Inlined.
rel(Ts, [Type]) ->
    case is_type(Type) andalso atoms_only(Type, 1) of
        true ->
            rel(Ts, tuple_size(Type), Type);
        false ->
            rel_type(Ts, [], Type)
    end;
rel(Ts, Sz) ->
    rel(Ts, Sz, erlang:make_tuple(Sz, ?ATOM_TYPE)).

atoms_only(Type, I) when ?IS_ATOM_TYPE(?REL_TYPE(I, Type)) ->
    atoms_only(Type, I+1);
atoms_only(Type, I) when I > tuple_size(Type), ?IS_RELATION(Type) ->
    true;
atoms_only(_Type, _I) ->
    false.

rel(Ts, Sz, Type) when Sz >= 1 ->
    SL = usort(Ts),
    rel(SL, SL, Sz, Type).

rel([T | Ts], L, Sz, Type) when tuple_size(T) =:= Sz ->
    rel(Ts, L, Sz, Type);
rel([], L, _Sz, Type) ->
    ?SET(L, Type).

rel_type([E | Ts], L, Type) ->
    {NType, NE} = make_element(E, Type, Type),
    rel_type(Ts, [NE | L], NType);
rel_type([], [], ?ANYTYPE) ->
    empty_set();
rel_type([], SL, Type) when ?IS_RELATION(Type) ->
    ?SET(usort(SL), Type).

%% Inlined.
a_func(Ts, T) ->
    case {T, is_type(T)} of
	{[?BINREL(DT, RT) = Type], true} when ?IS_ATOM_TYPE(DT),
					      ?IS_ATOM_TYPE(RT)  ->
	    func(Ts, Type);
	{[Type], true} ->
	    func_type(Ts, [], Type, fun(?BINREL(_,_)) -> true end)
    end.

func(L0, Type) ->
    L = usort(L0),
    func(L, L, L, Type).

func([{X,_} | Ts], X0, L, Type) when X /= X0 ->
    func(Ts, X, L, Type);
func([{X,_} | _Ts], X0, _L, _Type) when X == X0 ->
    bad_function;
func([], _X0, L, Type) ->
    ?SET(L, Type).

%% Inlined.
fam(Ts, T) ->
    case {T, is_type(T)} of
	{[?FAMILY(DT, RT) = Type], true} when ?IS_ATOM_TYPE(DT),
					      ?IS_ATOM_TYPE(RT)  ->
	    fam2(Ts, Type);
	{[Type], true} ->
	    func_type(Ts, [], Type, fun(?FAMILY(_,_)) -> true end)
    end.

fam2([], Type) ->
    ?SET([], Type);
fam2(Ts, Type) ->
    fam2(sort(Ts), Ts, [], Type).

fam2([{I,L} | T], I0, SL, Type) when I /= I0 ->
    fam2(T, I, [{I,usort(L)} | SL], Type);
fam2([{I,L} | T], I0, SL, Type) when I == I0 ->
    case {usort(L), SL} of
	{NL, [{_I,NL1} | _]} when NL == NL1 ->
	    fam2(T, I0, SL, Type);
	_ ->
	    bad_function
    end;
fam2([], _I0, SL, Type) ->
    ?SET(reverse(SL), Type).

func_type([E | T], SL, Type, F) ->
    {NType, NE} = make_element(E, Type, Type),
    func_type(T, [NE | SL], NType, F);
func_type([], [], ?ANYTYPE, _F) ->
    empty_set();
func_type([], SL, Type, F) ->
    true = F(Type),
    NL = usort(SL),
    check_function(NL, ?SET(NL, Type)).

setify(L, ?SET_OF(Atom)) when ?IS_ATOM_TYPE(Atom), Atom =/= ?ANYTYPE ->
    ?SET(usort(L), Atom);
setify(L, ?SET_OF(Type0)) ->
    try is_no_lists(Type0) of
        N when is_integer(N) ->
            rel(L, N, Type0);
        Sizes ->
            make_oset(L, Sizes, L, Type0)
    catch
        _:_ ->
            {?SET_OF(Type), Set} = create(L, Type0, Type0, []),
            ?SET(Set, Type)
    end;
setify(E, Type0) ->
    {Type, OrdSet} = make_element(E, Type0, Type0),
    ?ORDSET(OrdSet, Type).

is_no_lists(T) when is_tuple(T) ->
   Sz = tuple_size(T),
   is_no_lists(T, Sz, Sz, []).

is_no_lists(_T, 0, Sz, []) ->
   Sz;
is_no_lists(_T, 0, Sz, L) ->
   {Sz, L};
is_no_lists(T, I, Sz, L) when ?IS_ATOM_TYPE(?REL_TYPE(I, T)) ->
   is_no_lists(T, I-1, Sz, L);
is_no_lists(T, I, Sz, L) ->
   is_no_lists(T, I-1, Sz, [{I,is_no_lists(?REL_TYPE(I, T))} | L]).

create([E | Es], T, T0, L) ->
    {NT, S} = make_element(E, T, T0),
    create(Es, NT, T0, [S | L]);
create([], T, _T0, L) ->
    {?SET_OF(T), usort(L)}.

make_element(C, ?ANYTYPE, _T0) ->
    make_element(C);
make_element(C, Atom, ?ANYTYPE) when ?IS_ATOM_TYPE(Atom),
                                     not is_list(C), not is_tuple(C) ->
    {Atom, C};
make_element(C, Atom, Atom) when ?IS_ATOM_TYPE(Atom) ->
    {Atom, C};
make_element(T, TT, ?ANYTYPE) when tuple_size(T) =:= tuple_size(TT) ->
    make_tuple(tuple_to_list(T), tuple_to_list(TT), [], [], ?ANYTYPE);
make_element(T, TT, T0) when tuple_size(T) =:= tuple_size(TT) ->
    make_tuple(tuple_to_list(T), tuple_to_list(TT), [], [], tuple_to_list(T0));
make_element(L, [LT], ?ANYTYPE) when is_list(L) ->
    create(L, LT, ?ANYTYPE, []);
make_element(L, [LT], [T0]) when is_list(L) ->
    create(L, LT, T0, []).

make_tuple([E | Es], [T | Ts], NT, L, T0) when T0 =:= ?ANYTYPE ->
    {ET, ES} = make_element(E, T, T0),
    make_tuple(Es, Ts, [ET | NT], [ES | L], T0);
make_tuple([E | Es], [T | Ts], NT, L, [T0 | T0s]) ->
    {ET, ES} = make_element(E, T, T0),
    make_tuple(Es, Ts, [ET | NT], [ES | L], T0s);
make_tuple([], [], NT, L, _T0s) when NT =/= [] ->
    {list_to_tuple(reverse(NT)), list_to_tuple(reverse(L))}.

%% Derive type.
make_element(C) when not is_list(C), not is_tuple(C) ->
    {?ATOM_TYPE, C};
make_element(T) when is_tuple(T) ->
    make_tuple(tuple_to_list(T), [], []);
make_element(L) when is_list(L) ->
    create(L, ?ANYTYPE, ?ANYTYPE, []).

make_tuple([E | Es], T, L) ->
    {ET, ES} = make_element(E),
    make_tuple(Es, [ET | T], [ES | L]);
make_tuple([], T, L) when T =/= [] ->
    {list_to_tuple(reverse(T)),  list_to_tuple(reverse(L))}.

make_oset([T | Ts], Szs, L, Type) ->
    true = test_oset(Szs, T, T),
    make_oset(Ts, Szs, L, Type);
make_oset([], _Szs, L, Type) ->
    ?SET(usort(L), Type).

%% Optimization. Avoid re-building (nested) tuples.
test_oset({Sz,Args}, T, T0) when tuple_size(T) =:= Sz ->
    test_oset_args(Args, T, T0);
test_oset(Sz, T, _T0) when tuple_size(T) =:= Sz ->
    true.

test_oset_args([{Arg,Szs} | Ss], T, T0) ->
    true = test_oset(Szs, ?REL_TYPE(Arg, T), T0),
    test_oset_args(Ss, T, T0);
test_oset_args([], _T, _T0) ->
    true.

list_of_sets([S | Ss], Type, L) ->
    list_of_sets(Ss, Type, [?SET(S, Type) | L]);
list_of_sets([], _Type, L) ->
    reverse(L).

list_of_ordsets([S | Ss], Type, L) ->
    list_of_ordsets(Ss, Type, [?ORDSET(S, Type) | L]);
list_of_ordsets([], _Type, L) ->
    reverse(L).

tuple_of_sets([S | Ss], [?SET_OF(Type) | Types], L) ->
    tuple_of_sets(Ss, Types, [?SET(S, Type) | L]);
tuple_of_sets([S | Ss], [Type | Types], L) ->
    tuple_of_sets(Ss, Types, [?ORDSET(S, Type) | L]);
tuple_of_sets([], [], L) ->
    list_to_tuple(reverse(L)).

spec([E | Es], Fun, Type, L) ->
    case Fun(term2set(E, Type)) of
        true ->
            spec(Es, Fun, Type, [E | L]);
        false ->
            spec(Es, Fun, Type, L);
	_ ->
	    badarg
    end;
spec([], _Fun, _Type, L) ->
    reverse(L).

specification([E | Es], Fun, L) ->
    case Fun(E) of
        true ->
            specification(Es, Fun, [E | L]);
        false ->
            specification(Es, Fun, L);
	_ ->
	    badarg
    end;
specification([], _Fun, L) ->
    reverse(L).

%% Elements from the first list are kept.
intersection([H1 | T1], [H2 | T2], L) when H1 < H2 ->
    intersection1(T1, T2, L, H2);
intersection([H1 | T1], [H2 | T2], L) when H1 == H2 ->
    intersection(T1, T2, [H1 | L]);
intersection([H1 | T1], [_H2 | T2], L) ->
    intersection2(T1, T2, L, H1);
intersection(_, _, L) ->
    reverse(L).

intersection1([H1 | T1], T2, L, H2) when H1 < H2 ->
    intersection1(T1, T2, L, H2);
intersection1([H1 | T1], T2, L, H2) when H1 == H2 ->
    intersection(T1, T2, [H1 | L]);
intersection1([H1 | T1], T2, L, _H2) ->
    intersection2(T1, T2, L, H1);
intersection1(_, _, L, _) ->
    reverse(L).

intersection2(T1, [H2 | T2], L, H1) when H1 > H2 ->
    intersection2(T1, T2, L, H1);
intersection2(T1, [H2 | T2], L, H1) when H1 == H2 ->
    intersection(T1, T2, [H1 | L]);
intersection2(T1, [H2 | T2], L, _H1) ->
    intersection1(T1, T2, L, H2);
intersection2(_, _, L, _) ->
    reverse(L).

difference([H1 | T1], [H2 | T2], L) when H1 < H2 ->
    diff(T1, T2, [H1 | L], H2);
difference([H1 | T1], [H2 | T2], L) when H1 == H2 ->
    difference(T1, T2, L);
difference([H1 | T1], [_H2 | T2], L) ->
    diff2(T1, T2, L, H1);
difference(L1, _, L) ->
    reverse(L, L1).

diff([H1 | T1], T2, L, H2) when H1 < H2 ->
    diff(T1, T2, [H1 | L], H2);
diff([H1 | T1], T2, L, H2) when H1 == H2 ->
    difference(T1, T2, L);
diff([H1 | T1], T2, L, _H2) ->
    diff2(T1, T2, L, H1);
diff(_, _, L, _) ->
    reverse(L).

diff2(T1, [H2 | T2], L, H1) when H1 > H2 ->
    diff2(T1, T2, L, H1);
diff2(T1, [H2 | T2], L, H1) when H1 == H2 ->
    difference(T1, T2, L);
diff2(T1, [H2 | T2], L, H1) ->
    diff(T1, T2, [H1 | L], H2);
diff2(T1, _, L, H1) ->
    reverse(L, [H1 | T1]).

symdiff([H1 | T1], T2, L) ->
    symdiff2(T1, T2, L, H1);
symdiff(_, T2, L) ->
    reverse(L, T2).

symdiff1([H1 | T1], T2, L, H2) when H1 < H2 ->
    symdiff1(T1, T2, [H1 | L], H2);
symdiff1([H1 | T1], T2, L, H2) when H1 == H2 ->
    symdiff(T1, T2, L);
symdiff1([H1 | T1], T2, L, H2) ->
    symdiff2(T1, T2, [H2 | L], H1);
symdiff1(_, T2, L, H2) ->
    reverse(L, [H2 | T2]).

symdiff2(T1, [H2 | T2], L, H1) when H1 > H2 ->
    symdiff2(T1, T2, [H2 | L], H1);
symdiff2(T1, [H2 | T2], L, H1) when H1 == H2 ->
    symdiff(T1, T2, L);
symdiff2(T1, [H2 | T2], L, H1) ->
    symdiff1(T1, T2, [H1 | L], H2);
symdiff2(T1, _, L, H1) ->
    reverse(L, [H1 | T1]).

sympart([H1 | T1], [H2 | T2], L1, L12, L2, T) when H1 < H2 ->
    sympart1(T1, T2, [H1 | L1], L12, L2, T, H2);
sympart([H1 | T1], [H2 | T2], L1, L12, L2, T) when H1 == H2 ->
    sympart(T1, T2, L1, [H1 | L12], L2, T);
sympart([H1 | T1], [H2 | T2], L1, L12, L2, T) ->
    sympart2(T1, T2, L1, L12, [H2 | L2], T, H1);
sympart(S1, [], L1, L12, L2, T) ->
    {?SET(reverse(L1, S1), T),
     ?SET(reverse(L12), T),
     ?SET(reverse(L2), T)};
sympart(_, S2, L1, L12, L2, T) ->
    {?SET(reverse(L1), T),
     ?SET(reverse(L12), T),
     ?SET(reverse(L2, S2), T)}.

sympart1([H1 | T1], T2, L1, L12, L2, T, H2) when H1 < H2 ->
    sympart1(T1, T2, [H1 | L1], L12, L2, T, H2);
sympart1([H1 | T1], T2, L1, L12, L2, T, H2) when H1 == H2 ->
    sympart(T1, T2, L1, [H1 | L12], L2, T);
sympart1([H1 | T1], T2, L1, L12, L2, T, H2) ->
    sympart2(T1, T2, L1, L12, [H2 | L2], T, H1);
sympart1(_, T2, L1, L12, L2, T, H2) ->
    {?SET(reverse(L1), T),
     ?SET(reverse(L12), T),
     ?SET(reverse(L2, [H2 | T2]), T)}.

sympart2(T1, [H2 | T2], L1, L12, L2, T, H1) when H1 > H2 ->
    sympart2(T1, T2, L1, L12, [H2 | L2], T, H1);
sympart2(T1, [H2 | T2], L1, L12, L2, T, H1) when H1 == H2 ->
    sympart(T1, T2, L1, [H1 | L12], L2, T);
sympart2(T1, [H2 | T2], L1, L12, L2, T, H1) ->
    sympart1(T1, T2, [H1 | L1], L12, L2, T, H2);
sympart2(T1, _, L1, L12, L2, T, H1) ->
    {?SET(reverse(L1, [H1 | T1]), T),
     ?SET(reverse(L12), T),
     ?SET(reverse(L2), T)}.

prod([[E | Es] | Xs], T, L) ->
    prod(Es, Xs, T, prod(Xs, [E | T], L));
prod([], T, L) ->
    [list_to_tuple(reverse(T)) | L].

prod([E | Es], Xs, T, L) ->
    prod(Es, Xs, T, prod(Xs, [E | T], L));
prod([], _Xs, _E, L) ->
    L.

constant_function([E | Es], X, L) ->
    constant_function(Es, X, [{E,X} | L]);
constant_function([], _X, L) ->
    reverse(L).

subset([H1 | T1], [H2 | T2]) when H1 > H2 ->
    subset(T1, T2, H1);
subset([H1 | T1], [H2 | T2]) when H1 == H2 ->
    subset(T1, T2);
subset(L1, _) ->
    L1 =:= [].

subset(T1, [H2 | T2], H1) when H1 > H2 ->
    subset(T1, T2, H1);
subset(T1, [H2 | T2], H1) when H1 == H2 ->
    subset(T1, T2);
subset(_, _, _) ->
    false.

disjoint([B | Bs], A, As) when A < B ->
    disjoint(As, B, Bs);
disjoint([B | _Bs], A, _As) when A == B ->
    false;
disjoint([_B | Bs], A, As) ->
    disjoint(Bs, A, As);
disjoint(_Bs, _A, _As) ->
    true.

%% Append sets that come in order, then "merge".
lunion([[_] = S]) -> % optimization
    S;
lunion([[] | Ls]) ->
    lunion(Ls);
lunion([S | Ss]) ->
    umerge(lunion(Ss, last(S), [S], []));
lunion([]) ->
    [].

lunion([[E] = S | Ss], Last, SL, Ls) when E > Last -> % optimization
    lunion(Ss, E, [S | SL], Ls);
lunion([S | Ss], Last, SL, Ls) when hd(S) > Last ->
    lunion(Ss, last(S), [S | SL], Ls);
lunion([S | Ss], _Last, SL, Ls) ->
    lunion(Ss, last(S), [S], [append(reverse(SL)) | Ls]);
lunion([], _Last, SL, Ls) ->
    [append(reverse(SL)) | Ls].

%% The empty list is always the first list, if present.
lintersection(_, []) ->
    [];
lintersection([S | Ss], S0) ->
    lintersection(Ss, intersection(S, S0, []));
lintersection([], S) ->
    S.

can_rel([S | Ss], L) ->
    can_rel(Ss, L, S, S);
can_rel([], L) ->
    sort(L).

can_rel(Ss, L, [E | Es], S) ->
    can_rel(Ss, [{E, S} | L], Es, S);
can_rel(Ss, L, _, _S) ->
    can_rel(Ss, L).

rel2family([{X,Y} | S]) ->
    rel2fam(S, X, [Y], []);
rel2family([]) ->
    [].

rel2fam([{X,Y} | S], X0, YL, L) when X0 == X ->
    rel2fam(S, X0, [Y | YL], L);
rel2fam([{X,Y} | S], X0, [A,B | YL], L) -> % optimization
    rel2fam(S, X, [Y], [{X0,reverse(YL,[B,A])} | L]);
rel2fam([{X,Y} | S], X0, YL, L) ->
    rel2fam(S, X, [Y], [{X0,YL} | L]);
rel2fam([], X, YL, L) ->
    reverse([{X,reverse(YL)} | L]).

dom([{X,_} | Es]) ->
    dom([], X, Es);
dom([] = L) ->
    L.

dom(L, X, [{X1,_} | Es]) when X == X1 ->
    dom(L, X, Es);
dom(L, X, [{Y,_} | Es]) ->
    dom([X | L], Y, Es);
dom(L, X, []) ->
    reverse(L, [X]).

ran([{_,Y} | Es], L) ->
    ran(Es, [Y | L]);
ran([], L) ->
    usort(L).

relprod(A, B) ->
    usort(relprod1(A, B)).

relprod1([{Ay,Ax} | A], B) ->
    relprod1(B, Ay, Ax, A, []);
relprod1(_A, _B) ->
    [].

relprod1([{Bx,_By} | B], Ay, Ax, A, L) when Ay > Bx ->
    relprod1(B, Ay, Ax, A, L);
relprod1([{Bx,By} | B], Ay, Ax, A, L) when Ay == Bx ->
    relprod(B, Bx, By, A, [{Ax,By} | L], Ax, B, Ay);
relprod1([{Bx,By} | B], _Ay, _Ax, A, L) ->
    relprod2(B, Bx, By, A, L);
relprod1(_B, _Ay, _Ax, _A, L) ->
    L.

relprod2(B, Bx, By, [{Ay, _Ax} | A], L) when Ay < Bx ->
    relprod2(B, Bx, By, A, L);
relprod2(B, Bx, By, [{Ay, Ax} | A], L) when Ay == Bx ->
    relprod(B, Bx, By, A, [{Ax,By} | L], Ax, B, Ay);
relprod2(B, _Bx, _By, [{Ay, Ax} | A], L) ->
    relprod1(B, Ay, Ax, A, L);
relprod2(_, _, _, _, L) ->
    L.

relprod(B0, Bx0, By0, A0, L, Ax, [{Bx,By} | B], Ay) when Ay == Bx ->
    relprod(B0, Bx0, By0, A0, [{Ax,By} | L], Ax, B, Ay);
relprod(B0, Bx0, By0, A0, L, _Ax, _B, _Ay) ->
    relprod2(B0, Bx0, By0, A0, L).

relprod_n([], _R, _EmptyG, _IsR) ->
    {error, badarg};
relprod_n(RL, R, EmptyR, IsR) ->
    case domain_type(RL, ?ANYTYPE) of
        Error = {error, _Reason} ->
            Error;
        DType ->
            Empty = any(fun is_empty_set/1, RL) orelse EmptyR,
            RType = range_type(RL, []),
            Type = ?BINREL(DType, RType),
            Prod =
                case Empty of
                    true when DType =:= ?ANYTYPE; RType =:= ?ANYTYPE ->
                        empty_set();
                    true ->
                        ?SET([], Type);
                    false ->
                        TL = ?LIST((relprod_n(RL))),
                        Sz = length(RL),
                        Fun = fun({X,A}) -> {X, flat(Sz, A, [])} end,
                        ?SET(map(Fun, TL), Type)
                end,
            case IsR of
                true  -> relative_product(Prod, R);
                false -> Prod
            end
    end.

relprod_n([R | Rs]) ->
    relprod_n(Rs, R).

relprod_n([], R) ->
    R;
relprod_n([R | Rs], R0) ->
    T = raise_element(R0, 1),
    R1 = relative_product1(T, R),
    NR = projection({external, fun({{X,A},AS}) -> {X,{A,AS}} end}, R1),
    relprod_n(Rs, NR).

flat(1, A, L) ->
    list_to_tuple([A | L]);
flat(N, {T,A}, L) ->
    flat(N-1, T, [A | L]).

domain_type([T | Ts], T0) when ?IS_SET(T) ->
    case ?TYPE(T) of
        ?BINREL(DT, _RT) ->
            case unify_types(DT, T0) of
                [] -> {error, type_mismatch};
                T1 -> domain_type(Ts, T1)
            end;
        ?ANYTYPE ->
            domain_type(Ts, T0);
        _ -> {error, badarg}
    end;
domain_type([], T0) ->
    T0.

range_type([T | Ts], L) ->
    case ?TYPE(T) of
        ?BINREL(_DT, RT) ->
            range_type(Ts, [RT | L]);
        ?ANYTYPE ->
            ?ANYTYPE
    end;
range_type([], L) ->
    list_to_tuple(reverse(L)).

converse([{A,B} | X], L) ->
    converse(X, [{B,A} | L]);
converse([], L) ->
    sort(L).

strict([{E1,E2} | Es], L) when E1 == E2 ->
    strict(Es, L);
strict([E | Es], L) ->
    strict(Es, [E | L]);
strict([], L) ->
    reverse(L).

weak(Es) ->
    %% Not very efficient...
    weak(Es, ran(Es, []), []).

weak(Es=[{X,_} | _], [Y | Ys], L) when X > Y ->
    weak(Es, Ys, [{Y,Y} | L]);
weak(Es=[{X,_} | _], [Y | Ys], L) when X == Y ->
    weak(Es, Ys, L);
weak([E={X,Y} | Es], Ys, L) when X > Y ->
    weak1(Es, Ys, [E | L], X);
weak([E={X,Y} | Es], Ys, L) when X == Y ->
    weak2(Es, Ys, [E | L], X);
weak([E={X,_Y} | Es], Ys, L) -> % when X < _Y
    weak2(Es, Ys, [E, {X,X} | L], X);
weak([], [Y | Ys], L) ->
    weak([], Ys, [{Y,Y} | L]);
weak([], [], L) ->
    reverse(L).

weak1([E={X,Y} | Es], Ys, L, X0) when X > Y, X == X0 ->
    weak1(Es, Ys, [E | L], X);
weak1([E={X,Y} | Es], Ys, L, X0) when X == Y, X == X0 ->
    weak2(Es, Ys, [E | L], X);
weak1([E={X,_Y} | Es], Ys, L, X0) when X == X0 -> % when X < Y
    weak2(Es, Ys, [E, {X,X} | L], X);
weak1(Es, Ys, L, X) ->
    weak(Es, Ys, [{X,X} | L]).

weak2([E={X,_Y} | Es], Ys, L, X0) when X == X0 -> % when X < _Y
    weak2(Es, Ys, [E | L], X);
weak2(Es, Ys, L, _X) ->
    weak(Es, Ys, L).

extc(L, [D | Ds], C, Ts) ->
    extc(L, Ds, C, Ts, D);
extc(L, [], _C, _Ts) ->
    L.

extc(L, Ds, C, [{X,_Y} | Ts], D) when X < D ->
    extc(L, Ds, C, Ts, D);
extc(L, Ds, C, [{X,_Y} | Ts], D) when X == D ->
    extc(L, Ds, C, Ts);
extc(L, Ds, C, [{X,_Y} | Ts], D) ->
    extc2([{D,C} | L], Ds, C, Ts, X);
extc(L, Ds, C, [], D) ->
    extc_tail([{D,C} | L], Ds, C).

extc2(L, [D | Ds], C, Ts, X) when X > D ->
    extc2([{D,C} | L], Ds, C, Ts, X);
extc2(L, [D | Ds], C, Ts, X) when X == D ->
    extc(L, Ds, C, Ts);
extc2(L, [D | Ds], C, Ts, _X) ->
    extc(L, Ds, C, Ts, D);
extc2(L, [], _C, _Ts, _X) ->
    L.

extc_tail(L, [D | Ds], C) ->
    extc_tail([{D,C} | L], Ds, C);
extc_tail(L, [], _C) ->
    L.

is_a_func([{E,_} | Es], E0) when E /= E0 ->
    is_a_func(Es, E);
is_a_func(L, _E) ->
    L =:= [].

restrict_n(I, [T | Ts], Key, Keys, L) ->
    case element(I, T) of
	K when K < Key ->
	    restrict_n(I, Ts, Key, Keys, L);
	K when K == Key ->
	    restrict_n(I, Ts, Key, Keys, [T | L]);
	K ->
	    restrict_n(I, K, Ts, Keys, L, T)
    end;
restrict_n(_I, _Ts, _Key, _Keys, L) ->
    L.

restrict_n(I, K, Ts, [Key | Keys], L, E) when K > Key ->
    restrict_n(I, K, Ts, Keys, L, E);
restrict_n(I, K, Ts, [Key | Keys], L, E) when K == Key ->
    restrict_n(I, Ts, Key, Keys, [E | L]);
restrict_n(I, _K, Ts, [Key | Keys], L, _E) ->
    restrict_n(I, Ts, Key, Keys, L);
restrict_n(_I, _K, _Ts, _Keys, L, _E) ->
    L.

restrict([Key | Keys], Tuples) ->
    restrict(Tuples, Key, Keys, []);
restrict(_Keys, _Tuples) ->
    [].

restrict([{K,_E} | Ts], Key, Keys, L) when K < Key ->
    restrict(Ts, Key, Keys, L);
restrict([{K,E} | Ts], Key, Keys, L) when K == Key ->
    restrict(Ts, Key, Keys, [E | L]);
restrict([{K,E} | Ts], _Key, Keys, L) ->
    restrict(Ts, K, Keys, L, E);
restrict(_Ts, _Key, _Keys, L) ->
    L.

restrict(Ts, K, [Key | Keys], L, E) when K > Key ->
    restrict(Ts, K, Keys, L, E);
restrict(Ts, K, [Key | Keys], L, E) when K == Key ->
    restrict(Ts, Key, Keys, [E | L]);
restrict(Ts, _K, [Key | Keys], L, _E) ->
    restrict(Ts, Key, Keys, L);
restrict(_Ts, _K, _Keys, L, _E) ->
    L.

diff_restrict_n(I, [T | Ts], Key, Keys, L) ->
    case element(I, T) of
	K when K < Key ->
	    diff_restrict_n(I, Ts, Key, Keys, [T | L]);
	K when K == Key ->
	    diff_restrict_n(I, Ts, Key, Keys, L);
	K ->
	    diff_restrict_n(I, K, Ts, Keys, L, T)
    end;
diff_restrict_n(I, _Ts, _Key, _Keys, L) when I =:= 1 ->
    reverse(L);
diff_restrict_n(_I, _Ts, _Key, _Keys, L) ->
    sort(L).

diff_restrict_n(I, K, Ts, [Key | Keys], L, T) when K > Key ->
    diff_restrict_n(I, K, Ts, Keys, L, T);
diff_restrict_n(I, K, Ts, [Key | Keys], L, _T) when K == Key ->
    diff_restrict_n(I, Ts, Key, Keys, L);
diff_restrict_n(I, _K, Ts, [Key | Keys], L, T) ->
    diff_restrict_n(I, Ts, Key, Keys, [T | L]);
diff_restrict_n(I, _K, Ts, _Keys, L, T) when I =:= 1 ->
    reverse(L, [T | Ts]);
diff_restrict_n(_I, _K, Ts, _Keys, L, T) ->
    sort([T | Ts ++ L]).

diff_restrict([Key | Keys], Tuples) ->
    diff_restrict(Tuples, Key, Keys, []);
diff_restrict(_Keys, Tuples) ->
    diff_restrict_tail(Tuples, []).

diff_restrict([{K,E} | Ts], Key, Keys, L) when K < Key ->
    diff_restrict(Ts, Key, Keys, [E | L]);
diff_restrict([{K,_E} | Ts], Key, Keys, L) when K == Key ->
    diff_restrict(Ts, Key, Keys, L);
diff_restrict([{K,E} | Ts], _Key, Keys, L) ->
    diff_restrict(Ts, K, Keys, L, E);
diff_restrict(_Ts, _Key, _Keys, L) ->
    L.

diff_restrict(Ts, K, [Key | Keys], L, E) when K > Key ->
    diff_restrict(Ts, K, Keys, L, E);
diff_restrict(Ts, K, [Key | Keys], L, _E) when K == Key ->
    diff_restrict(Ts, Key, Keys, L);
diff_restrict(Ts, _K, [Key | Keys], L, E) ->
    diff_restrict(Ts, Key, Keys, [E | L]);
diff_restrict(Ts, _K, _Keys, L, E) ->
    diff_restrict_tail(Ts, [E | L]).

diff_restrict_tail([{_K,E} | Ts], L) ->
    diff_restrict_tail(Ts, [E | L]);
diff_restrict_tail(_Ts, L) ->
    L.

comp([], B) ->
    check_function(B, []);
comp(_A, []) ->
    bad_function;
comp(A0, [{Bx,By} | B]) ->
    A = converse(A0, []),
    check_function(A0, comp1(A, B, [], Bx, By)).

comp1([{Ay,Ax} | A], B, L, Bx, By) when Ay == Bx ->
    comp1(A, B, [{Ax,By} | L], Bx, By);
comp1([{Ay,Ax} | A], B, L, Bx, _By) when Ay > Bx ->
    comp2(A, B, L, Bx, Ay, Ax);
comp1([{Ay,_Ax} | _A], _B, _L, Bx, _By) when Ay < Bx ->
    bad_function;
comp1([], B, L, Bx, _By) ->
    check_function(Bx, B, L).

comp2(A, [{Bx,_By} | B], L, Bx0, Ay, Ax) when Ay > Bx, Bx /= Bx0 ->
    comp2(A, B, L, Bx, Ay, Ax);
comp2(A, [{Bx,By} | B], L, _Bx0, Ay, Ax) when Ay == Bx ->
    comp1(A, B, [{Ax,By} | L], Bx, By);
comp2(_A, _B, _L, _Bx0, _Ay, _Ax) ->
    bad_function.

inverse1([{A,B} | X]) ->
    inverse(X, A, [{B,A}]);
inverse1([]) ->
    [].

inverse([{A,B} | X], A0, L) when A0 /= A ->
    inverse(X, A, [{B,A} | L]);
inverse([{A,_B} | _X], A0, _L) when A0 == A ->
    bad_function;
inverse([], _A0, L) ->
    SL = [{V,_} | Es] = sort(L),
    case is_a_func(Es, V) of
	true -> SL;
	false -> bad_function
    end.

%% Inlined.
external_fun({external, Function}) when is_atom(Function) ->
    false;
external_fun({external, Fun}) ->
    Fun;
external_fun(_) ->
    false.

%% Inlined.
element_type(?SET_OF(Type)) -> Type;
element_type(Type) -> Type.

subst(Ts, Fun, Type) ->
    subst(Ts, Fun, Type, ?ANYTYPE, []).

subst([T | Ts], Fun, Type, NType, L) ->
    case setfun(T, Fun, Type, NType) of
	{SD, ST} -> subst(Ts, Fun, Type, ST, [{T, SD} | L]);
	Bad -> Bad
    end;
subst([], _Fun, _Type, NType, L) ->
    {L, NType}.

projection1([E | Es]) ->
    projection1([], element(1, E), Es);
projection1([] = L) ->
    L.

projection1(L, X, [E | Es]) ->
    case element(1, E) of
	X1 when X == X1 -> projection1(L, X, Es);
	X1 -> projection1([X | L], X1, Es)
    end;
projection1(L, X, []) ->
    reverse(L, [X]).

projection_n([E | Es], I, L) ->
    projection_n(Es, I, [element(I, E) | L]);
projection_n([], _I, L) ->
    usort(L).

substitute_element([T | Ts], I, L) ->
    substitute_element(Ts, I, [{T, element(I, T)} | L]);
substitute_element(_, _I, L) ->
    reverse(L).

substitute([T | Ts], Fun, L) ->
    substitute(Ts, Fun, [{T, Fun(T)} | L]);
substitute(_, _Fun, L) ->
    reverse(L).

partition_n(I, [E | Ts]) ->
    partition_n(I, Ts, element(I, E), [E], []);
partition_n(_I, []) ->
    [].

partition_n(I, [E | Ts], K, Es, P) ->
    case {element(I, E), Es} of
	{K1, _} when K == K1 ->
	    partition_n(I, Ts, K, [E | Es], P);
	{K1, [_]} -> % optimization
	    partition_n(I, Ts, K1, [E], [Es | P]);
	{K1, _} ->
	    partition_n(I, Ts, K1, [E], [reverse(Es) | P])
    end;
partition_n(I, [], _K, Es, P) when I > 1 ->
    sort([reverse(Es) | P]);
partition_n(_I, [], _K, [_] = Es, P) -> % optimization
    reverse(P, [Es]);
partition_n(_I, [], _K, Es, P) ->
    reverse(P, [reverse(Es)]).

partition3_n(I, [T | Ts], Key, Keys, L1, L2)  ->
    case element(I, T) of
	K when K < Key ->
	    partition3_n(I, Ts, Key, Keys, L1, [T | L2]);
	K when K == Key ->
	    partition3_n(I, Ts, Key, Keys, [T | L1], L2);
	K ->
	    partition3_n(I, K, Ts, Keys, L1, L2, T)
    end;
partition3_n(I, _Ts, _Key, _Keys, L1, L2) when I =:= 1 ->
    [reverse(L1) | reverse(L2)];
partition3_n(_I, _Ts, _Key, _Keys, L1, L2) ->
    [sort(L1) | sort(L2)].

partition3_n(I, K, Ts, [Key | Keys], L1, L2, T) when K > Key ->
    partition3_n(I, K, Ts, Keys, L1, L2, T);
partition3_n(I, K, Ts, [Key | Keys], L1, L2, T) when K == Key ->
    partition3_n(I, Ts, Key, Keys, [T | L1], L2);
partition3_n(I, _K, Ts, [Key | Keys], L1, L2, T) ->
    partition3_n(I, Ts, Key, Keys, L1, [T | L2]);
partition3_n(I, _K, Ts, _Keys, L1, L2, T) when I =:= 1 ->
    [reverse(L1) | reverse(L2, [T | Ts])];
partition3_n(_I, _K, Ts, _Keys, L1, L2, T) ->
    [sort(L1) | sort([T | Ts ++ L2])].

partition3([Key | Keys], Tuples) ->
    partition3(Tuples, Key, Keys, [], []);
partition3(_Keys, Tuples) ->
    partition3_tail(Tuples, [], []).

partition3([{K,E} | Ts], Key, Keys, L1, L2) when K < Key ->
    partition3(Ts, Key, Keys, L1, [E | L2]);
partition3([{K,E} | Ts], Key, Keys, L1, L2) when K == Key ->
    partition3(Ts, Key, Keys, [E | L1], L2);
partition3([{K,E} | Ts], _Key, Keys, L1, L2) ->
    partition3(Ts, K, Keys, L1, L2, E);
partition3(_Ts, _Key, _Keys, L1, L2) ->
    [L1 | L2].

partition3(Ts, K, [Key | Keys], L1, L2, E) when K > Key ->
    partition3(Ts, K, Keys, L1, L2, E);
partition3(Ts, K, [Key | Keys], L1, L2, E) when K == Key ->
    partition3(Ts, Key, Keys, [E | L1], L2);
partition3(Ts, _K, [Key | Keys], L1, L2, E) ->
    partition3(Ts, Key, Keys, L1, [E | L2]);
partition3(Ts, _K, _Keys, L1, L2, E) ->
    partition3_tail(Ts, L1, [E | L2]).

partition3_tail([{_K,E} | Ts], L1, L2) ->
    partition3_tail(Ts, L1, [E | L2]);
partition3_tail(_Ts, L1, L2) ->
    [L1 | L2].

replace([E | Es], F, L) ->
    replace(Es, F, [F(E) | L]);
replace(_, _F, L) ->
    sort(L).

mul_relprod([T | Ts], I, R) when ?IS_SET(T) ->
    P = raise_element(R, I),
    F = relative_product1(P, T),
    [F | mul_relprod(Ts, I+1, R)];
mul_relprod([], _I, _R) ->
    [].

raise_element(R, I) ->
    L = sort(I =/= 1, rearr(?LIST(R), I, [])),
    Type = ?TYPE(R),
    ?SET(L, ?BINREL(?REL_TYPE(I, Type), Type)).

rearr([E | Es], I, L) ->
    rearr(Es, I, [{element(I, E), E} | L]);
rearr([], _I, L) ->
    L.

join_element(E1, E2) ->
    [_ | L2] = tuple_to_list(E2),
    list_to_tuple(tuple_to_list(E1) ++ L2).

join_element(E1, E2, I2) ->
    tuple_to_list(E1) ++ join_element2(tuple_to_list(E2), 1, I2).

join_element2([B | Bs], C, I2) when C =/= I2 ->
    [B | join_element2(Bs, C+1, I2)];
join_element2([_ | Bs], _C, _I2) ->
    Bs.

family2rel([{X,S} | F], L) ->
    fam2rel(F, L, X, S);
family2rel([], L) ->
    reverse(L).

fam2rel(F, L, X, [Y | Ys]) ->
    fam2rel(F, [{X,Y} | L], X, Ys);
fam2rel(F, L, _X, _) ->
    family2rel(F, L).

fam_spec([{_,S}=E | F], Fun, Type, L) ->
    case Fun(?SET(S, Type)) of
        true ->
            fam_spec(F, Fun, Type, [E | L]);
        false ->
            fam_spec(F, Fun, Type, L);
	_ ->
	    badarg
    end;
fam_spec([], _Fun, _Type, L) ->
    reverse(L).

fam_specification([{_,S}=E | F], Fun, L) ->
    case Fun(S) of
        true ->
            fam_specification(F, Fun, [E | L]);
        false ->
            fam_specification(F, Fun, L);
	_ ->
	    badarg
    end;
fam_specification([], _Fun, L) ->
    reverse(L).

un_of_fam([{_X,S} | F], L) ->
    un_of_fam(F, [S | L]);
un_of_fam([], L) ->
    lunion(sort(L)).

int_of_fam([{_,S} | F]) ->
    int_of_fam(F, [S]);
int_of_fam([]) ->
    badarg.

int_of_fam([{_,S} | F], L) ->
    int_of_fam(F, [S | L]);
int_of_fam([], [L | Ls]) ->
    lintersection(Ls, L).

fam_un([{X,S} | F], L) ->
    fam_un(F, [{X, lunion(S)} | L]);
fam_un([], L) ->
    reverse(L).

fam_int([{X, [S | Ss]} | F], L) ->
    fam_int(F, [{X, lintersection(Ss, S)} | L]);
fam_int([{_X,[]} | _F], _L) ->
    badarg;
fam_int([], L) ->
    reverse(L).

fam_dom([{X,S} | F], L) ->
    fam_dom(F, [{X, dom(S)} | L]);
fam_dom([], L) ->
    reverse(L).

fam_ran([{X,S} | F], L) ->
    fam_ran(F, [{X, ran(S, [])} | L]);
fam_ran([], L) ->
    reverse(L).

fam_union(F1 = [{A,_AS} | _AL], [B1={B,_BS} | BL], L) when A > B ->
    fam_union(F1, BL, [B1 | L]);
fam_union([{A,AS} | AL], [{B,BS} | BL], L) when A == B ->
    fam_union(AL, BL, [{A, umerge(AS, BS)} | L]);
fam_union([A1 | AL], F2, L) ->
    fam_union(AL, F2, [A1 | L]);
fam_union(_, F2, L) ->
    reverse(L, F2).

fam_intersect(F1 = [{A,_AS} | _AL], [{B,_BS} | BL], L) when A > B ->
    fam_intersect(F1, BL, L);
fam_intersect([{A,AS} | AL], [{B,BS} | BL], L) when A == B ->
    fam_intersect(AL, BL, [{A, intersection(AS, BS, [])} | L]);
fam_intersect([_A1 | AL], F2, L) ->
    fam_intersect(AL, F2, L);
fam_intersect(_, _, L) ->
    reverse(L).

fam_difference(F1 = [{A,_AS} | _AL], [{B,_BS} | BL], L) when A > B ->
    fam_difference(F1, BL, L);
fam_difference([{A,AS} | AL], [{B,BS} | BL], L) when A == B ->
    fam_difference(AL, BL, [{A, difference(AS, BS, [])} | L]);
fam_difference([A1 | AL], F2, L) ->
    fam_difference(AL, F2, [A1 | L]);
fam_difference(F1, _, L) ->
    reverse(L, F1).

check_function([{X,_} | XL], R) ->
    check_function(X, XL, R);
check_function([], R) ->
    R.

check_function(X0, [{X,_} | XL], R) when X0 /= X ->
    check_function(X, XL, R);
check_function(X0, [{X,_} | _XL], _R) when X0 == X ->
    bad_function;
check_function(_X0, [], R) ->
    R.

fam_partition_n(I, [E | Ts]) ->
    fam_partition_n(I, Ts, element(I, E), [E], []);
fam_partition_n(_I, []) ->
    [].

fam_partition_n(I, [E | Ts], K, Es, P) ->
    case {element(I, E), Es} of
	{K1, _} when K == K1 ->
	    fam_partition_n(I, Ts, K, [E | Es], P);
	{K1, [_]} -> % optimization
	    fam_partition_n(I, Ts, K1, [E], [{K,Es} | P]);
	{K1, _} ->
	    fam_partition_n(I, Ts, K1, [E], [{K,reverse(Es)} | P])
    end;
fam_partition_n(_I, [], K, [_] = Es, P) -> % optimization
    reverse(P, [{K,Es}]);
fam_partition_n(_I, [], K, Es, P) ->
    reverse(P, [{K,reverse(Es)}]).

fam_partition([{K,Vs} | Ts], Sort) ->
    fam_partition(Ts, K, [Vs], [], Sort);
fam_partition([], _Sort) ->
    [].

fam_partition([{K1,V} | Ts], K, Vs, P, S) when K1 == K ->
    fam_partition(Ts, K, [V | Vs], P, S);
fam_partition([{K1,V} | Ts], K, [_] = Vs, P, S) -> % optimization
    fam_partition(Ts, K1, [V], [{K, Vs} | P], S);
fam_partition([{K1,V} | Ts], K, Vs, P, S) ->
    fam_partition(Ts, K1, [V], [{K, sort(S, Vs)} | P], S);
fam_partition([], K, [_] = Vs, P, _S) -> % optimization
    [{K, Vs} | P];
fam_partition([], K, Vs, P, S) ->
    [{K, sort(S, Vs)} | P].

fam_proj([{X,S} | F], Fun, Type, NType, L) ->
    case setfun(S, Fun, Type, NType) of
	{SD, ST} -> fam_proj(F, Fun, Type, ST, [{X, SD} | L]);
	Bad -> Bad
    end;
fam_proj([], _Fun, _Type, NType, L) ->
    {reverse(L), NType}.

setfun(T, Fun, Type, NType) ->
    case Fun(term2set(T, Type)) of
	NS when ?IS_SET(NS) ->
	    case unify_types(NType, ?SET_OF(?TYPE(NS))) of
		[] -> type_mismatch;
		NT -> {?LIST(NS), NT}
	    end;
	NS when ?IS_ORDSET(NS) ->
            NT = ?ORDTYPE(NS),
	    case unify_types(NType, NT) of
		[] -> type_mismatch;
		NT -> {?ORDDATA(NS), NT}
	    end;
	_ ->
	    badarg
    end.

%% Inlined.
term2set(L, Type) when is_list(L) ->
    ?SET(L, Type);
term2set(T, Type) ->
    ?ORDSET(T, Type).

fam2digraph(F, G) ->
    Fun = fun({From, ToL}) ->
                  digraph:add_vertex(G, From),
                  Fun2 = fun(To) ->
                                 digraph:add_vertex(G, To),
                                 case digraph:add_edge(G, From, To) of
                                     {error, {bad_edge, _}} ->
                                         throw({error, cyclic});
                                     _ ->
                                         true
                                 end
                         end,
                  foreach(Fun2, ToL)
          end,
    foreach(Fun, to_external(F)),
    G.

digraph_family(G) ->
    Vs = sort(digraph:vertices(G)),
    digraph_fam(Vs, Vs, G, []).

digraph_fam([V | Vs], V0, G, L) when V /= V0 ->
    Ns = sort(digraph:out_neighbours(G, V)),
    digraph_fam(Vs, V, G, [{V,Ns} | L]);
digraph_fam([], _V0, _G, L) ->
    reverse(L).

%% -> boolean()
check_fun(T, F, FunT) ->
    true = is_type(FunT),
    {NT, _MaxI} = number_tuples(T, 1),
    L = flatten(tuple2list(F(NT))),
    has_hole(L, 1).

number_tuples(T, N) when is_tuple(T) ->
    {L, NN} = mapfoldl(fun number_tuples/2, N, tuple_to_list(T)),
    {list_to_tuple(L), NN};
number_tuples(_, N) ->
    {N, N+1}.

tuple2list(T) when is_tuple(T) ->
    map(fun tuple2list/1, tuple_to_list(T));
tuple2list(C) ->
    [C].

has_hole([I | Is], I0) when I =< I0 -> has_hole(Is, erlang:max(I+1, I0));
has_hole(Is, _I) -> Is =/= [].

%% Optimization. Same as check_fun/3, but for integers.
check_for_sort(T, _I) when T =:= ?ANYTYPE ->
    empty;
check_for_sort(T, I) when ?IS_RELATION(T), I =< ?REL_ARITY(T), I >= 1 ->
    I > 1;
check_for_sort(_T, _I) ->
    error.

inverse_substitution(L, Fun, Sort) ->
    %% One easily sees that the inverse of the tuples created by
    %% applying Fun need to be sorted iff the tuples created by Fun
    %% need to be sorted.
    sort(Sort, fun_rearr(L, Fun, [])).

fun_rearr([E | Es], Fun, L) ->
    fun_rearr(Es, Fun, [{Fun(E), E} | L]);
fun_rearr([], _Fun, L) ->
    L.

sets_to_list(Ss) ->
    map(fun(S) when ?IS_SET(S) -> ?LIST(S) end, Ss).

types([], L) ->
    list_to_tuple(reverse(L));
types([S | _Ss], _L) when ?TYPE(S) =:= ?ANYTYPE ->
    ?ANYTYPE;
types([S | Ss], L) ->
    types(Ss, [?TYPE(S) | L]).

%% Inlined.
unify_types(T, T) -> T;
unify_types(Type1, Type2) ->
    try
        unify_types1(Type1, Type2)
    catch
        throw:Val ->
            Val
    end.

unify_types1(Atom, Atom) when ?IS_ATOM_TYPE(Atom) ->
    Atom;
unify_types1(?ANYTYPE, Type) ->
    Type;
unify_types1(Type, ?ANYTYPE) ->
    Type;
unify_types1(?SET_OF(Type1), ?SET_OF(Type2)) ->
    [unify_types1(Type1, Type2)];
unify_types1(T1, T2) when tuple_size(T1) =:= tuple_size(T2) ->
    unify_typesl(tuple_size(T1), T1, T2, []);
unify_types1(_T1, _T2) ->
    throw([]).

unify_typesl(0, _T1, _T2, L) ->
    list_to_tuple(L);
unify_typesl(N, T1, T2, L) ->
    T = unify_types1(?REL_TYPE(N, T1), ?REL_TYPE(N, T2)),
    unify_typesl(N-1, T1, T2, [T | L]).

%% inlined.
match_types(T, T) -> true;
match_types(Type1, Type2) -> match_types1(Type1, Type2).

match_types1(Atom, Atom) when ?IS_ATOM_TYPE(Atom) ->
    true;
match_types1(?ANYTYPE, _) ->
    true;
match_types1(_, ?ANYTYPE) ->
    true;
match_types1(?SET_OF(Type1), ?SET_OF(Type2)) ->
    match_types1(Type1, Type2);
match_types1(T1, T2) when tuple_size(T1) =:= tuple_size(T2) ->
    match_typesl(tuple_size(T1), T1, T2);
match_types1(_T1, _T2) ->
    false.

match_typesl(0, _T1, _T2) ->
    true;
match_typesl(N, T1, T2) ->
    case match_types1(?REL_TYPE(N, T1), ?REL_TYPE(N, T2)) of
        true  -> match_typesl(N-1, T1, T2);
        false -> false
    end.

sort(true, L) ->
    sort(L);
sort(false, L) ->
    reverse(L).
