dif/2 incorrect Ⅵ

[UWN]

?- dif(A,B),A=[[]|A],B=[C|D],D=[_|_],D=[[]|C].
false, unexpected.
?- dif(A,B),A=[[]|A],B=[C|D],        D=[[]|C].
A = [[]|A],
B = [C, []|C],
D = [[]|C].

[UWN]

Just noted that this is the very same of the first test #122

In any case, there is now a new version for finite terms:

?- dif(A,B),A=[[]|C],B=[D|A],C=[_|_],C=[[]|D].
   false, unexpected.
?-          A=[[]|C],B=[D|A],C=[_|_],C=[[]|D],dif(A,B).
   A = [[], []|D],
   C = [[]|D],
   B = [D, [], []|D].

[UWN]

All 9.1.12

[hyperswine]

interesting, the query system in SWI prolog is a bit strange as well in my experience. For this specific example it might be more related to the implementation of dif/2 though