Definition corestep_plus c m c' m' :=
    exists n, corestepN (S n) c m c' m'.Definition corestep_star c m c' m' :=
    exists n, corestepN n c m c' m'.

Lemma memsem_preservesN P (HP: memstep_preserve P) n c m c' m' (H: corestepN M n c m c' m'): P m m'.