Definition minimal (gamma : flist) (work : nf_list) 
  (context : flist) :=
  forall (a : form) (k : kripke_tree),
  Is_Monotone_kripke_tree k ->
  forces_gamma gamma work k -> In a context -> forces_t k a.

Lemma minimal_cons_gamma_weak : forall (gamma : flist) (work : nf_list) (context : flist) (a b : form), (forall k : kripke_tree, Is_Monotone_kripke_tree k -> forces_t k b -> forces_t k a) -> minimal (a :: gamma) work context -> minimal (b :: gamma) work context.