proposition: Lemma setI_impl_r {T} (s1 s2 : set T) : s2 \subset s1 -> s1 :&: s2 <--> s2.
proof: Proof. firstorder. Qed.
imports: mathcomp.ssreflect.ssreflect Classes.RelationClasses Classes.Morphisms List Tactics mathcomp(ssrfun ssrbool ssrnat seq)