intros work ds x ni ai a.
apply In_Nested_Imps with 0; simpl in |- *; apply My_NthO.
Qed.

Lemma in_ngamma_cons_ni_rev :
forall (work : nf_list) (ds : disjs) (x : nested_imp)
(ni : nested_imps) (ai : atomic_imps) (a : atoms)
(c : normal_form),
in_ngamma work ds (x :: ni) ai a c ->
in_ngamma work ds ni ai a c + {c = NImp_NF (nested_imp2nimp x)}.