Inductive ev_plus ge: state -> mem -> _ -> state -> mem -> Prop :=
| ev_plus_left: forall s1 m1 ev1 s2 m2 ev2 s3 m3,
ev_step (CLC_evsem ge) s1 m1 ev1 s2 m2 -> ev_star ge s2 m2 ev2 s3 m3 ->
ev_plus ge s1 m1 (ev1 ++ ev2) s3 m3.

Lemma ev_plus_two:
forall ge s1 m1 ev1 s2 m2 ev2 s3 m3,
ev_step (CLC_evsem ge) s1 m1 ev1 s2 m2 -> ev_step (CLC_evsem ge) s2 m2 ev2 s3 m3 ->
ev_plus ge s1 m1 (ev1 ++ ev2) s3 m3.