Inductive plus: state -> state -> Prop :=
| plus_left: forall s1 s2 s3,
CCstep s1 s2 -> star s2 s3 -> plus s1 s3.

Lemma strip_step:
forall ge ve te k m st' m',
cl_step ge (State ve te (strip_skip k)) m st' m' <->
cl_step ge (State ve te k) m st' m'.