% Examples of the effect of forcing a predicate to backtrack by failure.
poem(N) :-
	open(A, N),
	!,
	closer(B, N),
	append(A,B,AB),
	append(AB,'.', C),
	 write(C), nl.

closer(C, 0) :-
	!,
	fail.
closer(C, N) :-
	N > 0,
	contin(C).
closer(C, N) :-
	N > 0,
	contin(C1),
	N1 is N - 1,
	closer(C2, N1),
	append(C1, C2, C).

contin(' is a rose').
open('A rose', _).

:- write('Predicate poem(N). loaded'), nl.