proposition: Lemma leb_negb_gtb : forall x y, x <=? y = negb (y <? x).
proof: Proof. intros x y;apply Bool.eq_true_iff_eq;split;intros. apply Bool.eq_true_not_negb;apply leb_not_gtb;trivial. rewrite Bool.negb_true_iff, <- Bool.not_true_iff_false in H. rewrite leb_spec; rewrite ltb_spec in H;lia. Qed.
imports: Bool List PArray Int63 Ring63 ZArith Psatz