:- dynamic answers_to_skip/1.

ppp2 :-
	findall(pp(Head,Body),pp(Head,Body),Program1),
	reverse_program(Program1,[],Program2),
	repeat(0,N),
	find_nth_answer(N,Program1,Answer1),
	find_nth_answer(N,Program2,Answer2),
	( Answer1 == nomore, Answer2 == nomore ->
	    !                   % stop the repeat and succeed
	; is_a_copy(Answer1,Answer2) ->
	    fail                % ok, try next answers
	;
	    !,
	    fail                % different answers found: fail
	).
ppp2.

find_nth_answer(N,Program,Goal) :-
	Goal = run(_),
	set_answers_to_skip(N),
	exec(Goal,Program),
	answers_to_skip(M),
	( M == 0 ->
	    !
	;
	    NewM is M - 1,
	    set_answers_to_skip(NewM),
	    fail
	).
find_nth_answer(_,_,nomore).

repeat(I,I).
repeat(I,J) :-
	I1 is I + 1,
	repeat(I1,J).

set_answers_to_skip(N) :-
	retractall(answers_to_skip(_)),
	assert(answers_to_skip(N)).