:- import numbervars/3 from num_vars.

:- table a/2.

/* ?- a(Q,W), a(W,W), a(f(F),f(F)) , a([F],[F]) */

a(X,Y) :- p(X,Y).
a(X,Y) :- a(X,Z),p(Z,Y).

testcombo :- 
	(tw(_Q,_W),fail ; tw(A,A),fail ; tw(f(F),f(F)),fail ; tw([F],[F]),fail).

tw(Q,W) :- a(Q,W),T = a(Q,W),numbervars(T,0,_T1),writeq(T),nl.

p(f(1),f(2)).
p(f(2),f(3)).
p(f(3),f(1)).

p([1],[2]).
p([2],[3]).
p([3],[1]).

p(f([1]),f([2])).
p(f([2]),f([3])).
p(f([3]),f([1])).

p([f(1)],[f(2)]).
p([f(2)],[f(3)]).
p([f(3)],[f(1)]).