proposition: Lemma setI_bigcup_assoc {A B} (s1 : set B) (s2 : set A) (s3 : A -> set B) : s1 :&: (\bigcup_(x in s2) s3 x) <--> \bigcup_(x in s2) (s1 :&: (s3 x)).
proof: Proof. firstorder. Qed.
imports: mathcomp.ssreflect.ssreflect Classes.RelationClasses Classes.Morphisms List Tactics mathcomp(ssrfun ssrbool ssrnat seq)