Lemma jsafe_corestep_forward: forall {Espec: OracleKind} ge c m c' m' n z, jstep (cl_core_sem ge) c m c' m' -> jsafeN (@OK_spec Espec) ge (S n) z c m -> jm_bupd z (jsafeN (@OK_spec Espec) ge n z c') m'.