intuition.
eapply evalDet_steps_done_skipn_h; eauto.
Qed.

Lemma evalDet_steps_skipn_h : forall (A : Set) a1 (x y : comp_state A),
evalDet_steps x y ->
forall (c : Comp A)(a2 : A) s1 s2,
x = (cs_more c s1) ->
y = (cs_done a2 s2) ->
In a1 (getSupport c) ->
(a1 = a2 \/ (exists n, n > 0 /\ s2 = skipn n s1)).