Incorrect behaviour for a simple logical disjunction.

[RECHE23]

With this code:

test1(A, B) :- member(A, [true, false]), member(B, [true, false]), (A ; B).
test2(A, B) :- member(A, [true, false]), member(B, [true, false]), (((A ; B) -> true) ; A ; B).

I get this result:

1 ?- test1(A, B).
A = B, B = true ;
A = B, B = true ;
A = true,
B = false ;
A = false,
B = true ;
false.

2 ?- test2(A, B).
A = B, B = true ;
A = true,
B = false ;
A = false,
B = true ;
false.

For a simple logical disjunction, I don't see any logical reason why A = B, B = true appears twice in test1(A, B).

Both expressions should behave the same way since they are logically equivalent.

[JanWielemaker]

Prolog does not remove duplicate answers. You can do so using tabling or distinct/1. Please do not use the issues pages for basic Prolog questions. Use the forum on Discourse or Stackoverflow.

[RECHE23]

Prolog does not remove duplicate answers. You can do so using tabling or distinct/1. Please do not use the issues pages for basic Prolog questions. Use the forum on Discourse or Stackoverflow.

So you don't see any flaw in this? This is really the expected behaviour?

[JanWielemaker]

Try discourse, I'm not going to read this in all detail. Just, logically equivalent answers are part of normal Prolog SLD resolution.