Currently unify allows using sets as expressions and just uses them as sequences, which, depending on the order of items, causes the unification to fail or succeed:
(unify #{ '[aa a] '[bb b] } ; =seq=> [bb b] [aa a]
#{ '[?a a] '[?b b] } ; =seq=> [?b b] [?a a]
) ; => {?a aa, ?b bb}
(unify #{ '[a a] '[b b] } ; =seq=> [a a] [b b]
#{ '[?a a] '[?b b] } ; =seq=> [?b b] [?a a]
) ; => nil, expected {?a a, ?b b}
Unify should either handle sets (not sure if the algorithm allows for that easily) or throw an IllegalArgumentException when passed a set, but not silently seq it and behave unpredictably like that.
