+(**************************************************************************)
+(* ___ *)
+(* ||M|| *)
+(* ||A|| A project by Andrea Asperti *)
+(* ||T|| *)
+(* ||I|| Developers: *)
+(* ||T|| The HELM team. *)
+(* ||A|| http://helm.cs.unibo.it *)
+(* \ / *)
+(* \ / This file is distributed under the terms of the *)
+(* v GNU General Public License Version 2 *)
+(* *)
+(**************************************************************************)
+
+
+
+(* NORMAL FORM PREDICATE FOR PROOFS IN CONTEXT
+ For cut elimination
+*)
+
+include "PEq/defs.ma".
+include "PRed/defs.ma".
+
+inductive PNF (P:Context) (p:Proof): Prop \def
+ | pnf: (\forall q,Q,S. [P, p, S] => [Q, q, S] \to [P, p] = [Q, q]) \to
+ PNF P p
+.