proposition: Lemma setU_set0_r {A} (s1 s2 s3 : set A) : s1 <--> set0 -> s3 <--> s2 -> s3 <--> (s1 :|: s2).
proof: Proof. firstorder. Qed.
imports: mathcomp.ssreflect.ssreflect Classes.RelationClasses Classes.Morphisms List Tactics mathcomp(ssrfun ssrbool ssrnat seq)