proposition: Lemma n0n1_or_gt : forall n : nat, n = 0 \/ n = 1 \/ n > 1.
proof: Proof. intro n. case n. left. reflexivity. intro n1. case n1. right. left. reflexivity. intro n2. right. right. apply gt_n_S. apply gt_Sn_O. Qed.
imports: ZArith EqNat