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diff --git a/matita/library/Z/inversion.ma b/matita/library/Z/inversion.ma
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+(**************************************************************************)
+(*       ___	                                                            *)
+(*      ||M||                                                             *)
+(*      ||A||       A project by Andrea Asperti                           *)
+(*      ||T||                                                             *)
+(*      ||I||       Developers:                                           *)
+(*      ||T||       A.Asperti, C.Sacerdoti Coen,                          *)
+(*      ||A||       E.Tassi, S.Zacchiroli                                 *)
+(*      \   /                                                             *)
+(*       \ /        Matita is distributed under the terms of the          *)
+(*        v         GNU Lesser General Public License Version 2.1         *)
+(*                                                                        *)
+(**************************************************************************)
+
+set "baseuri" "cic:/matita/Z/inversion".
+
+include "Z/dirichlet_product.ma".
+include "Z/moebius.ma".
+
+definition sigma_div: (nat \to Z) \to nat \to Z \def
+\lambda f.\lambda n. sigma_p (S n) (\lambda d.divides_b d n) f.
+
+theorem sigma_div_moebius:
+\forall n:nat. O < n \to sigma_div moebius n = is_one n.
+intros.elim H
+  [reflexivity
+  |rewrite > is_one_OZ  
+    [unfold sigma_div.
+     apply sigma_p_moebius.
+     apply le_S_S.
+     assumption
+    |unfold Not.intro.
+     apply (lt_to_not_eq ? ? H1).
+     apply injective_S.
+     apply sym_eq.
+     assumption
+    ]
+  ]
+qed.
+  
+(* moebius inversion theorem *)
+theorem inversion: \forall f:nat \to Z.\forall n:nat.O < n \to
+dirichlet_product moebius (sigma_div f) n = f n.
+intros.
+rewrite > commutative_dirichlet_product
+  [apply (trans_eq ? ? (dirichlet_product (dirichlet_product f (\lambda n.Zone)) moebius n))
+    [unfold dirichlet_product.
+     apply eq_sigma_p1;intros
+      [reflexivity
+      |apply eq_f2
+        [apply sym_eq.
+         unfold sigma_div.
+         apply dirichlet_product_one_r.
+         apply (divides_b_true_to_lt_O ? ? H H2)
+        |reflexivity
+        ]
+      ]
+    |rewrite > associative_dirichlet_product
+      [apply (trans_eq ? ? (dirichlet_product f (sigma_div moebius) n))
+        [unfold dirichlet_product.
+         apply eq_sigma_p1;intros
+          [reflexivity
+          |apply eq_f2
+            [reflexivity
+            |unfold sigma_div.
+             apply dirichlet_product_one_l.
+             apply (lt_times_n_to_lt x)
+              [apply (divides_b_true_to_lt_O ? ? H H2)
+              |rewrite > divides_to_div
+                [assumption
+                |apply (divides_b_true_to_divides ? ? H2)
+                ]
+              ]
+            ]
+          ]
+        |apply (trans_eq ? ? (dirichlet_product f is_one n))
+          [unfold dirichlet_product.
+           apply eq_sigma_p1;intros
+            [reflexivity
+            |apply eq_f2
+              [reflexivity
+              |apply sigma_div_moebius.
+               apply (lt_times_n_to_lt x)
+                [apply (divides_b_true_to_lt_O ? ? H H2)
+                |rewrite > divides_to_div
+                  [assumption
+                  |apply (divides_b_true_to_divides ? ? H2)
+                  ]
+                ]
+              ]
+            ]
+          |apply dirichlet_product_is_one_r
+          ]
+        ]
+      |assumption
+      ]
+    ]
+  |assumption
+  ]
+qed.
+        
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