proposition: Lemma setI_setU_distr {U} (s1 s2 s3 : set U) : ((s1 :|: s2) :&: s3) <--> ((s1 :&: s3) :|: (s2 :&: s3)).
proof: Proof. firstorder. Qed.
imports: mathcomp.ssreflect.ssreflect Classes.RelationClasses Classes.Morphisms List Tactics mathcomp(ssrfun ssrbool ssrnat seq)