induction 1; intuition; simpl in *; subst.
discriminate.
inversion H1; clear H1; subst.
inversion H0; clear H0; subst.
eapply evalDet_step_done_skipn; eauto.
symmetry in H.
specialize (evalDet_step_more_skipn _  _ H); intuition.
destruct H0.
subst.
edestruct IHevalDet_steps.
eauto.
eauto.
subst.
exists (x + x0).
apply skipn_sum.
Qed.

Lemma evalDet_steps_done_skipn : forall (A : Set)(c : Comp A) s a s',
evalDet_steps (cs_more c s) (cs_done a s') ->
exists n, s' = skipn n s.