forall a b : nat, a <= b |_| b < a. Proof. induction a as [|a IHa]. - intros;left;apply zero_least. - intros [|b]. + right. apply lt_0_S. + destruct (IHa b). * left. apply le_S_S;trivial. * right. apply le_S_S. trivial. Defined.
Require Import