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

Lemma strip_skip_not:
forall s k, s<>Sskip -> strip_skip (Kseq s :: k) = (Kseq s :: k).