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diff --git a/matita/contribs/LOGIC/datatypes_defs/Formula.ma b/matita/contribs/LOGIC/datatypes_defs/Formula.ma
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+(**************************************************************************)
+(*       ___                                                              *)
+(*      ||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                  *)
+(*                                                                        *)
+(**************************************************************************)
+
+
+
+(* FORMULAE
+   - Naming policy:
+     - formulae: a b c d
+*)
+
+include "preamble0.ma".
+
+inductive Formula: Type \def
+   | posr: Nat \to Formula
+   | impl: Formula \to Formula \to Formula
+.