proposition: Lemma dropLast_plus_last : forall (l1: list A) a b, last (a :: l1) = Some b -> dropLast (a :: l1) ++ b :: nil = a :: l1.
proof: Proof. induction l1. simpl; intros. inversion H; trivial. intros. simpl. rewrite <- (IHl1 a b); trivial. Qed.
imports: Coq(Permutation Setoid) CoLoR(NatUtil LogicUtil)