proposition: Fact Forall_filter X (P : X -> Prop) (f : X -> bool) ll : Forall P ll -> Forall P (filter f ll).
proof: Proof. induction 1; simpl; auto; destruct (f x); auto. Qed.
imports: List Arith Lia Permutation Undecidability.Shared.Libs.DLW.Utils(list_focus utils_tac)