proposition: Lemma setI_set_eq_r {A : Type} (s1 s2 s2' : set A) : s2 <--> s2' -> (s1 :&: s2) <--> (s1 :&: s2').
proof: Proof. intros. rewrite H; reflexivity. Qed.
imports: mathcomp.ssreflect.ssreflect Classes.RelationClasses Classes.Morphisms List Tactics mathcomp(ssrfun ssrbool ssrnat seq)