Hi all,
While Doing a Prolog college assignment, I faced the following strange problem:
occured_once(X, List) is true iff X occured once in List:
occured_once(X, [X]).
occured_once(H, [H | T]) :-
\+ member(H, T).
occured_once(X, [H | T]) :-
\+ X = H,
occured_once(X, T).
Compiling and executing above snipped, here's some queries:
| ?- occured_once(1, [1, 2, X]).
no
| ?- occured_once(1, [1, 2, 3]).
true ?
yes
So How come first test says that no X satisfy the first query, while it says
that the second query is true (same query substiuting X with 3) ?.
$ gprolog --version
Prolog top-Level (GNU Prolog) 1.2.18
Thanks,
--
Ahmed S. Darwish
http://darwish.07.googlepages.com
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