Section Transport.
(* Assume that P reaches a halting configuration from (0, 1) after NP steps, show that M is uniformly bounded. *)
Variable NP : nat. (* number of steps  *)
Variable NP_spec : CM.halting P (Nat.iter NP (CM.step P) cm_start).
Definition cm_end := Nat.iter NP (CM.step P) cm_start. (* final configuration *)
Definition CP : nat := CM.value cm_end. (* final counter value *)

Lemma index_no_step_shape {y l r i} :
SMX.step M (l, r, '#-i) y -> (r = [§0] ++ skipn 1 r).