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