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Obtaining the still possible elements of a set (lub\glb)
- A set variable.
- A set.
Poss is unified with the set of still possible elements of SetVariable
(i.e. its lub\glb).
If SetVariable is a set of sets and a union function attribute has been set,
then each element of Poss comes annotated with its respective length.
Fails if Poss can not be unified with the current poss (lub\glb) of SetVariable.
?- S `::[c]+[a,b], poss(S,P).
P = [a,b]
?- S `::[[c]]+[[a,b]], poss(S,P).
P = [[a,b]]
?- set(S, ,[[a,b],[b,c],[a,c],[b]],[union:[a,b,c]]), poss(S,P).
P = [[a, b] : 2, [a, c] : 2, [b] : 1, [b, c] : 2]
glb / 2, glb_poss / 3, domain / 2, domain / 3, lub / 2, lub / 4