proposition: Lemma lem_lst : forall {A} (x : A) l1 l2 (P : A -> Prop), In x (l1 ++ l2) -> (forall y, In y l1 -> P y) -> (forall y, In y l2 -> P y) -> P x.
proof: Proof. sauto db: slist. Qed.
imports: Hammer(Tactics) Arith ZArith List Lia Hammer(Hints)