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