cut (Zlog_sup M <= w). omega. rewrite <- Zlog_sup_pow with (i := w). apply Zlog_sup_seq.
apply Zle_trans with (2 ^ (w - 1)). apply Mset_r. apply Zlt_le_weak. apply lt_2wm1_2w.
exact le_0_w. cut (1 <= Zlog_sup M). omega.
replace 1 with  (Zlog_sup 2). apply Zlog_sup_seq. omega. trivial. replace 1 with (0 * M + 1).
symmetry. apply Zdiv_mult_plus. omega. omega. omega. ring. intro H0. rewrite <- H0. simpl.
replace (1 / 1) with 1. cut (0 < w). omega. exact lt_0_w. trivial. apply Mset_l. Qed.

Lemma in_Z__if_in_Mset : forall M : Mset, in_Z_ (2 ^ w) M.
intro M. unfold in_Z_. case M. unfold in_Mset. simpl. intros. cut (2 ^ (w - 1) < 2 ^ w). omega.