intros i work ds ni ai a a' context equiv_ins mon.
unfold nminimal in |- *.
intros c k k_is_mon k_forces_ngamma in_a.
apply mon; try assumption.
apply forces_ngamma_shift_a_work with a'; assumption.
Qed.

Lemma nminimal_shift_work_ni_x_ni :
forall (x : nested_imp) (work : nf_list) (ds : disjs)
(ni1 ni2 : nested_imps) (ai : atomic_imps) (a : atoms)
(context : flist),
nminimal (NImp_NF (nested_imp2nimp x) :: work) ds (ni1 ++ ni2) ai a context ->
nminimal work ds (ni1 ++ x :: ni2) ai a context.