case z. intro. absurd (1 < 0); omega. simpl. intros p H0. rewrite <- two_p_pow. rewrite <- two_p_pow.
replace (log_sup p - 1) with (Zpred (log_sup p)). apply log_sup_correct2. unfold Zpred. ring. apply log_sup_correct1.
generalize H0. case p. simpl. intros q H1. cut (0 <= log_inf q). omega. apply log_inf_correct1. simpl.
intros q H1. cut (0 <= log_sup q). omega. apply log_sup_correct1. intro. absurd (1 < 1); omega.
intros p H0. absurd (1 < Zneg p). simplify_eq. assumption. Qed.

(* Specifications: *)
Lemma Zlog_sup_unique : forall z : Z, 0 < z -> forall i j : Z, 0 <= i -> 0 <= j ->
2 ^ (i - 1) < z -> z <= 2 ^ i -> 2 ^ (j - 1) < z -> z <= 2 ^ j -> i = j.