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' (CC.Kseq s k) = (CC.Kseq s k).