(* File: In_Gamma.v  (last edited on 27/10/2000) (c) Klaus Weich  *)
Require Export In_NGamma.
Inductive in_gamma (gamma : flist) (work : nf_list) : form -> Set :=
| In_Gamma :
forall (n : nat) (a : form),
my_nth form n gamma a -> in_gamma gamma work a
| In_Work1 :
forall (n : nat) (a : normal_form),
my_nth normal_form n work a -> in_gamma gamma work (nf2form a).
intros a gamma work c in_gamma0.
elim in_gamma0; clear in_gamma0 c.
intros n c nth.
apply In_Gamma with (S n).
apply My_NthS; assumption.
intros n c nth.
apply In_Work1 with n; assumption.
Qed.
intros a gamma work.
apply In_Gamma with 0.
apply My_NthO.
Qed.
intros a gamma work c in_gamma0.
elim in_gamma0; clear in_gamma0 c.
intros n c; case n; clear n.
intros nth.
right; inversion_clear nth; trivial.
intros n nth.
left; apply In_Gamma with n.
inversion_clear nth; assumption.
intros n c nth.
left; apply In_Work1 with n; assumption.
Qed.
intros a gamma work c in_gamma0.
elim in_gamma0; clear in_gamma0 c.
intros n c nth.
apply In_Gamma with n; assumption.
intros n c nth.
apply In_Work1 with (S n).
apply My_NthS; assumption.
Qed.

Lemma in_gamma_cons_work_head :
forall (a : normal_form) (gamma : flist) (work : nf_list),
in_gamma gamma (a :: work) (nf2form a).