proposition: Lemma ltb_leb_sub1 : forall x i, x <> 0 -> (i <? x = true <-> i <=? x - 1 = true).
proof: Proof. intros x i Hdiff. rewrite ltb_spec, leb_spec, to_Z_sub_1_diff;trivial. split;auto with zarith. Qed.
imports: Bool List PArray Int63 Ring63 ZArith Psatz