(* File: Sound.v  (last edited on 27/10/2000) (c) Klaus Weich  *)
Require Export NSound.
Require Export In_Gamma.
Definition sound (Gamma : flist) (work : nf_list) (context : flist) :=
forall a : form, in_gamma Gamma work a -> Derivable context a.

Lemma sound_cons_gamma :
forall (gamma : flist) (work : nf_list) (context : flist) (a : form),
Derivable context a ->
sound gamma work context -> sound (a :: gamma) work context.