free c:channel.
fun h(bitstring):bitstring.

event e(bitstring).
event e'(bitstring).

query x:bitstring; putbegin event:e; event (e'(x)).

process 
	new s:bitstring;
	(
		event e(s);
		out(c,h(s))
	) | (
		in(c,=h(s));
		event e'(h(s))
	)
