induction n; intuition; simpl in *.
rewrite shiftOut_0 in H.
inversion H; clear H; subst.
trivial.
destruct s;
simpl in *.
discriminate.
case_eq (shiftOut s n); intuition;
rewrite H0 in H.
destruct p.
inversion H; clear H; subst.
eauto.
discriminate.
Qed.

(* Specifications: *)
Lemma evalDet_step_more_skipn_eq : forall (A : Set)(c c' : Comp A)(a1 : A) s1 s2,
evalDet_step c s1 = (cs_more c' s2) ->
In a1 (getSupport c) ->
(s1 = s2 \/ (exists n, n > 0 /\ s2 = skipn n s1)).