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diff --git a/helm/matita/library/nat/totient.ma b/helm/matita/library/nat/totient.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                                 *)
+(*      \   /                                                             *)
+(*       \ /        This file is distributed under the terms of the       *)
+(*        v         GNU Lesser General Public License Version 2.1         *)
+(*                                                                        *)
+(**************************************************************************)
+
+set "baseuri" "cic:/matita/nat/totient".
+
+include "nat/count.ma".
+include "nat/chinese_reminder.ma".
+
+definition totient : nat \to nat \def
+\lambda n. count n (\lambda m. eqb (gcd m n) (S O)).
+
+theorem totient3: totient (S(S(S O))) = (S(S O)).
+reflexivity.
+qed.
+
+theorem totient6: totient (S(S(S(S(S(S O)))))) = (S(S O)).
+reflexivity.
+qed.
+
+theorem totient_times: \forall n,m:nat. (gcd m n) = (S O) \to
+totient (n*m) = (totient n)*(totient m).
+intro.
+apply (nat_case n).
+intro.simplify.intro.reflexivity.
+intros 2.apply (nat_case m1).
+rewrite < sym_times.
+rewrite < (sym_times (totient O)).
+simplify.intro.reflexivity.
+intros.
+unfold totient.
+apply (count_times m m2 ? ? ? 
+(\lambda b,a. cr_pair (S m) (S m2) a b) (\lambda x. x \mod (S m)) (\lambda x. x \mod (S m2))).
+intros.unfold cr_pair.
+apply (le_to_lt_to_lt ? (pred ((S m)*(S m2)))).
+unfold min.
+apply le_min_aux_r.
+change with ((S (pred ((S m)*(S m2)))) \le ((S m)*(S m2))).
+apply (nat_case ((S m)*(S m2))).apply le_n.
+intro.apply le_n.
+intros.
+generalize in match (mod_cr_pair (S m) (S m2) a b H1 H2 H).
+intro.elim H3.
+apply H4.
+intros.
+generalize in match (mod_cr_pair (S m) (S m2) a b H1 H2 H).
+intro.elim H3.
+apply H5.
+intros.
+generalize in match (mod_cr_pair (S m) (S m2) a b H1 H2 H).
+intro.elim H3.
+apply eqb_elim.
+intro.
+rewrite > eq_to_eqb_true.
+rewrite > eq_to_eqb_true.
+reflexivity.
+rewrite < H4.
+rewrite > sym_gcd.
+rewrite > gcd_mod.
+apply (gcd_times_SO_to_gcd_SO ? ? (S m2)).
+unfold lt.apply le_S_S.apply le_O_n.
+unfold lt.apply le_S_S.apply le_O_n.
+assumption.
+unfold lt.apply le_S_S.apply le_O_n.
+rewrite < H5.
+rewrite > sym_gcd.
+rewrite > gcd_mod.
+apply (gcd_times_SO_to_gcd_SO ? ? (S m)).
+unfold lt.apply le_S_S.apply le_O_n.
+unfold lt.apply le_S_S.apply le_O_n.
+rewrite > sym_times.
+assumption.
+unfold lt.apply le_S_S.apply le_O_n.
+intro.
+apply eqb_elim.
+intro.apply eqb_elim.
+intro.apply False_ind.
+apply H6.
+apply eq_gcd_times_SO.
+unfold lt.apply le_S_S.apply le_O_n.
+unfold lt.apply le_S_S.apply le_O_n.
+rewrite < gcd_mod.
+rewrite > H4.
+rewrite > sym_gcd.assumption.
+unfold lt.apply le_S_S.apply le_O_n.
+rewrite < gcd_mod.
+rewrite > H5.
+rewrite > sym_gcd.assumption.
+unfold lt.apply le_S_S.apply le_O_n.
+intro.reflexivity.
+intro.reflexivity.
+qed.
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