intros work ds ni1 ni2 ai a c le12 in_ngamma.
apply in_ngamma_eqv with ni1.
apply le_eqv; assumption.
assumption.
Qed.

Lemma in_ngamma_ge :
forall (work : nf_list) (ds : disjs) (ni1 ni2 : nested_imps)
(ai : atomic_imps) (a : atoms) (c : normal_form),
le_ni ni2 ni1 ->
in_ngamma work ds ni1 ai a c -> in_ngamma work ds ni2 ai a c.