proposition: Lemma filter_cons : forall x l P, filter P (x::l) = (If P x then x :: filter P l else filter P l).
proof: Proof. Proof using. auto. Qed.
imports: Coq.Classes.Morphisms TLC(LibTactics LibLogic LibReflect LibOperation LibProd LibOption LibNat LibInt LibWf LibMonoid LibRelation)