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