(* File: Forces_Gamma.v  (last edited on 27/10/2000) (c) Klaus Weich  *)
Require Export In_Gamma.
Require Export Forces_NGamma.
Definition forces_gamma (gamma : flist) (work : nf_list)
(k : kripke_tree) := forall a : form, in_gamma gamma work a -> forces_t k a.
intros gamma work k a forces_a forces_gamma0.
unfold forces_gamma in |- *.
intros c in_gamma0.
elim (in_gamma_cons_gamma_rev a gamma work c in_gamma0); clear in_gamma0.
intros in_gamma0.
apply forces_gamma0; assumption.
intros eq_c;  rewrite eq_c; assumption.
Qed.
intros gamma work k a forces_gamma0.
unfold forces_gamma in |- *.
intros c in_gamma0.
apply forces_gamma0.
apply in_gamma_cons_gamma_tail; assumption.
Qed.
intros gamma work k a forces_gamma0.
apply forces_gamma0.
apply in_gamma_cons_gamma_head; assumption.
Qed.
(*********************************************************************)
intros a gamma work k forces_gamma0.
unfold forces_gamma in |- *.
intros c in_gamma.
apply forces_gamma0.
apply in_gamma_shift_work_gamma; assumption.
Qed.
intros a gamma work k forces_gamma0.
unfold forces_gamma in |- *.
intros c in_gamma.
apply forces_gamma0.
apply in_gamma_shift_gamma_work; assumption.
Qed.
(*********************************************************************)

Lemma forces_gamma_cons_gamma_weak :
forall (gamma : flist) (work : nf_list) (k : kripke_tree) (a b : form),
(forces_t k a -> forces_t k b) ->
forces_gamma (a :: gamma) work k -> forces_gamma (b :: gamma) work k.