Definition last_successor :=
  root legal_config no_copy_measure no_copy_succ decidable_no_copy_succ
    no_copy_succ_decreases.

(* Specifications: *)
Lemma last_successor_is_last : forall y0 y : legal_config, ~ no_copy_succ y (last_successor y0).
Lemma last_successor_has_no_message : forall y0 : legal_config, no_message (get_c (last_successor y0)).