proposition: Lemma log2_up_succ_or : forall a, log2_up (S a) == S (log2_up a) \/ log2_up (S a) == log2_up a.
proof: Proof. intros a. destruct (le_gt_cases (log2_up (S a)) (log2_up a)) as [H|H]. - right. generalize (log2_up_le_mono _ _ (le_succ_diag_r a)); order. - left. apply le_succ_l in H. generalize (log2_up_succ_le a); order. Qed.
imports: NZAxioms NZMulOrder NZPow