Remark forces_ngamma_del_ai :
 forall (i : Int) (work : nf_list) (ds : disjs) (ni : nested_imps)
   (ai ai' : atomic_imps) (a : atoms) (k : kripke_tree),
 EQUIV_DEL nf_list i ai ai' ->
 forces_ngamma work ds ni ai a k -> forces_ngamma work ds ni ai' a k.

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