induction n. intros d r. intro H.
replace (foldlz f' (d, r) 1) with (f' (d, r) (x_ 0)).
(* replace w with ((Z_of_nat 0 + 1) * w). *) (* does not work *)
cut (P M p (fst (f' (d, r) (x_ 0))) (snd (f' (d, r) (x_ 0))) (x / 2 ^ ((Z_of_nat 0 + 1) * w)) (x_ 0)). (* workaroud *)
replace ((Z_of_nat 0 + 1) * w) with w. (* works *) trivial. ring. apply P'f'x. assumption. trivial. intros d r. intro H.
replace (foldlz f' (d, r) (S (S n))) with (foldlz f' (f' (d, r) (x_ (S n))) (S n)).
replace (f' (d, r) (x_ (S n))) with (d_i M_in_Z_ ptM'cM'' (d, r) (x_ (S n)), r_i M_in_Z_ ptM'cM'' (d, r) (x_ (S n))). apply IHn.
replace (Z_of_nat n + 2) with (Z_of_nat (S n) + 1).
replace (d_i M_in_Z_ ptM'cM'' (d, r) (x_ (S n))) with (fst (f' (d, r) (x_ (S n)))).
replace (r_i M_in_Z_ ptM'cM'' (d, r) (x_ (S n))) with (snd (f' (d, r) (x_ (S n)))).
apply P'f'x. assumption. trivial. trivial. rewrite inj_S. unfold Zsucc. ring. trivial. trivial. Qed.

Lemma P_S : forall (n : nat),
0 <= x -> x < 2 ^ (Z_of_nat (S n) * w) ->
P M p (fst (foldlz f' (zero_in_Z_, zero_in_Z_) (S n)))
(snd (foldlz f' (zero_in_Z_, zero_in_Z_) (S n))) (x / 2 ^ w) (x_ 0).