If this constraint is not solved, this predicate delays until it can be completely solved.
[eclipse 2]: S `:: {}.. {1,2,3}, [S1,S2] `:: {}..{3,4,5}, S \/ S1 `= S2. S = S{{} .. {3}} S1 = S1{{} .. {3, 4, 5}} S2 = S2{{} .. {3, 4, 5}} Delayed goals: union_s(S{{} .. {3}}, S1{{} .. {3, 4, 5}}, S2{{} .. {3, 4, 5}}) yes.