intros work ds ni1 ni2 ai a c eqv12 ini1.
apply in_ngamma_ni_eq with ni1; try assumption.
apply eqv_nimps_eq; assumption.
Qed.

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