:- use_module(library(lists), [flatten/2, member/2]).

choices(Goal,ChoiceList) :-
	exec(Goal,Multis),
	elim_dupl(Multis,ChoiceList).

exec((A,B),MultiAB) :- !,
	exec(A,MultiA),
	findall(Multi,(A,exec(B,Multi)),MultiB),
	flatten([MultiA,MultiB],MultiAB).
exec(true,[]) :- !.
exec(Head,MultiH) :-
	findall(Multi,(clause(Head,Body),exec(Body,Multi)),BodyMultis),
	(
	  BodyMultis == [] ->
	    MultiH = []
	;
	  BodyMultis = [MultiH] ->
	    true
	;
	    copy_term(Head,HeadC),
	    flatten([HeadC|BodyMultis],MultiH)
	).

elim_dupl([],[]).
elim_dupl([X|R],Out) :-
	( member(Y,R), variants(Y,X) ->
	    elim_dupl(R,Out)
	;
	    Out = [X|NewOut],
	    elim_dupl(R,NewOut)
	).

variants(X,Y) :-
	\+ \+ (numbervars(X,1,N),numbervars(Y,1,N),X = Y).