Definition effstep_plus U c m c' m' :=
exists n, effstepN (S n) U c m c' m'.
Definition effstep_star U c m c' m' :=
exists n, effstepN n U c m c' m'.

Lemma effstep_plus_star : forall U c1 c2 m1 m2,
effstep_plus U c1 m1 c2 m2 -> effstep_star U c1 m1 c2 m2.