intros x work ds ni1 ni2 ai a context min.
unfold nminimal in |- *.
intros c k k_is_mon k_forces_ngamma in_c.
apply min; try assumption.
apply forces_ngamma_shift_work_ni_x_ni; assumption.
Qed.
(********************************************************************)

Lemma nminimal_cons_work_strength :
forall (b c : normal_form) (work : nf_list) (ds : disjs)
(ni : nested_imps) (ai : atomic_imps) (a : atoms)
(context : flist),
(forall k : kripke_tree,
Is_Monotone_kripke_tree k ->
forces_ngamma (c :: work) ds ni ai a k -> forces_t k (nf2form b)) ->
nminimal (b :: work) ds ni ai a context ->
nminimal (c :: work) ds ni ai a context.