iso_dif/2 is much simpler to implement than a comparison: The built-in \= operator is available You now exactly what arguments to provide to\= Definition Based on your comments, the safe comparison means that the order won’t change if variables in both subterms are instanciated. If we name the comparison lt, we have for example: lt(a(X), … Read more
First try! The following code is based on the meta-predicates tfilter/3 and tpartition/4, the monotone if-then-else control construct if_/3, the reified unary logical connective not_t/3, and the reified term equality predicate (=)/3: different([],[_|_]). different([X|Xs0],Ys0) :- tpartition(=(X),Ys0,Es,Ys1), if_(Es=[], true, (tfilter(not_t(=(X)),Xs0,Xs1),different(Xs1,Ys1))). Sample query: ?- different([A,B],[X,Y]). A=Y , dif(B,Y), X=Y ; A=X , B=X , dif(X,Y) ; A=X … Read more
Well for one thing, the name should be more declarative, like equality_truth/2.
In place of not(X = Y) you need to write \+ X = Y or X \= Y. But consider to use dif(X,Y) instead. dif/2 is present in B, SWI, YAP, SICStus. To see the difference: ?- X = b, dif(a, X). X = b. ?- X = b, \+ a = X. X = … Read more