Remark starN_star:
  forall ge n s t s', starN ge n s t s' -> star ge s t s'.Remark star_starN:
  forall ge s t s', star ge s t s' -> exists n, starN ge n s t s'.

(* Specifications: *)
Lemma forever_N_forever: forall ge a s T, forever_N ge a s T -> forever ge s T.
Lemma forever_plus_forever: forall ge s T, forever_plus ge s T -> forever ge s T.