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diff --git a/helm/matita/library/nat/nth_prime.ma b/helm/matita/library/nat/nth_prime.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/nat/nth_prime".
-
-include "nat/primes.ma".
-include "nat/lt_arith.ma".
-
-(* upper bound by Bertrand's conjecture. *)
-(* Too difficult to prove.        
-let rec nth_prime n \def
-match n with
-  [ O \Rightarrow (S(S O))
-  | (S p) \Rightarrow
-    let previous_prime \def S (nth_prime p) in
-    min_aux previous_prime ((S(S O))*previous_prime) primeb].
-
-theorem example8 : nth_prime (S(S O)) = (S(S(S(S(S O))))).
-normalize.reflexivity.
-qed.
-
-theorem example9 : nth_prime (S(S(S O))) = (S(S(S(S(S(S(S O))))))).
-normalize.reflexivity.
-qed.
-
-theorem example10 : nth_prime (S(S(S(S O)))) = (S(S(S(S(S(S(S(S(S(S(S O))))))))))).
-normalize.reflexivity.
-qed. *)
-
-theorem smallest_factor_fact: \forall n:nat.
-n < smallest_factor (S n!).
-intros.
-apply not_le_to_lt.
-change with (smallest_factor (S n!) \le n \to False).intro.
-apply (not_divides_S_fact n (smallest_factor(S n!))).
-apply lt_SO_smallest_factor.
-unfold lt.apply le_S_S.apply le_SO_fact.
-assumption.
-apply divides_smallest_factor_n.
-unfold lt.apply le_S_S.apply le_O_n.
-qed.
-
-theorem ex_prime: \forall n. (S O) \le n \to \exists m.
-n < m \land m \le S n! \land (prime m).
-intros.
-elim H.
-apply (ex_intro nat ? (S(S O))).
-split.split.apply (le_n (S(S O))).
-apply (le_n (S(S O))).apply (primeb_to_Prop (S(S O))).
-apply (ex_intro nat ? (smallest_factor (S (S n1)!))).
-split.split.
-apply smallest_factor_fact.
-apply le_smallest_factor_n.
-(* Andrea: ancora hint non lo trova *)
-apply prime_smallest_factor_n.
-change with ((S(S O)) \le S (S n1)!).
-apply le_S.apply le_SSO_fact.
-unfold lt.apply le_S_S.assumption.
-qed.
-
-let rec nth_prime n \def
-match n with
-  [ O \Rightarrow (S(S O))
-  | (S p) \Rightarrow
-    let previous_prime \def (nth_prime p) in
-    let upper_bound \def S previous_prime! in
-    min_aux (upper_bound - (S previous_prime)) upper_bound primeb].
-    
-(* it works, but nth_prime 4 takes already a few minutes -
-it must compute factorial of 7 ...
-
-theorem example11 : nth_prime (S(S O)) = (S(S(S(S(S O))))).
-normalize.reflexivity.
-qed.
-
-theorem example12: nth_prime (S(S(S O))) = (S(S(S(S(S(S(S O))))))).
-normalize.reflexivity.
-qed.
-
-theorem example13 : nth_prime (S(S(S(S O)))) = (S(S(S(S(S(S(S(S(S(S(S O))))))))))).
-normalize.reflexivity.
-*) 
-
-theorem prime_nth_prime : \forall n:nat.prime (nth_prime n).
-intro.
-apply (nat_case n).
-change with (prime (S(S O))).
-apply (primeb_to_Prop (S(S O))).
-intro.
-change with
-(let previous_prime \def (nth_prime m) in
-let upper_bound \def S previous_prime! in
-prime (min_aux (upper_bound - (S previous_prime)) upper_bound primeb)).
-apply primeb_true_to_prime.
-apply f_min_aux_true.
-apply (ex_intro nat ? (smallest_factor (S (nth_prime m)!))).
-split.split.
-cut (S (nth_prime m)!-(S (nth_prime m)! - (S (nth_prime m))) = (S (nth_prime m))).
-rewrite > Hcut.exact (smallest_factor_fact (nth_prime m)).
-(* maybe we could factorize this proof *)
-apply plus_to_minus.
-apply plus_minus_m_m.
-apply le_S_S.
-apply le_n_fact_n.
-apply le_smallest_factor_n.
-apply prime_to_primeb_true.
-apply prime_smallest_factor_n.
-change with ((S(S O)) \le S (nth_prime m)!).
-apply le_S_S.apply le_SO_fact.
-qed.
-
-(* properties of nth_prime *)
-theorem increasing_nth_prime: increasing nth_prime.
-change with (\forall n:nat. (nth_prime n) < (nth_prime (S n))).
-intros.
-change with
-(let previous_prime \def (nth_prime n) in
-let upper_bound \def S previous_prime! in
-(S previous_prime) \le min_aux (upper_bound - (S previous_prime)) upper_bound primeb).
-intros.
-cut (upper_bound - (upper_bound -(S previous_prime)) = (S previous_prime)).
-rewrite < Hcut in \vdash (? % ?).
-apply le_min_aux.
-apply plus_to_minus.
-apply plus_minus_m_m.
-apply le_S_S.
-apply le_n_fact_n.
-qed.
-
-variant lt_nth_prime_n_nth_prime_Sn :\forall n:nat. 
-(nth_prime n) < (nth_prime (S n)) \def increasing_nth_prime.
-
-theorem injective_nth_prime: injective nat nat nth_prime.
-apply increasing_to_injective.
-apply increasing_nth_prime.
-qed.
-
-theorem lt_SO_nth_prime_n : \forall n:nat. (S O) \lt nth_prime n.
-intros. elim n.unfold lt.apply le_n.
-apply (trans_lt ? (nth_prime n1)).
-assumption.apply lt_nth_prime_n_nth_prime_Sn.
-qed.
-
-theorem lt_O_nth_prime_n : \forall n:nat. O \lt nth_prime n.
-intros.apply (trans_lt O (S O)).
-unfold lt. apply le_n.apply lt_SO_nth_prime_n.
-qed.
-
-theorem ex_m_le_n_nth_prime_m: 
-\forall n: nat. nth_prime O \le n \to 
-\exists m. nth_prime m \le n \land n < nth_prime (S m).
-intros.
-apply increasing_to_le2.
-exact lt_nth_prime_n_nth_prime_Sn.assumption.
-qed.
-
-theorem lt_nth_prime_to_not_prime: \forall n,m. nth_prime n < m \to m < nth_prime (S n) 
-\to \lnot (prime m).
-intros.
-apply primeb_false_to_not_prime.
-letin previous_prime \def (nth_prime n).
-letin upper_bound \def (S previous_prime!).
-apply (lt_min_aux_to_false primeb upper_bound (upper_bound - (S previous_prime)) m).
-cut (S (nth_prime n)!-(S (nth_prime n)! - (S (nth_prime n))) = (S (nth_prime n))).
-rewrite > Hcut.assumption.
-apply plus_to_minus.
-apply plus_minus_m_m.
-apply le_S_S.
-apply le_n_fact_n.
-assumption.
-qed.
-
-(* nth_prime enumerates all primes *)
-theorem prime_to_nth_prime : \forall p:nat. prime p \to
-\exists i. nth_prime i = p.
-intros.
-cut (\exists m. nth_prime m \le p \land p < nth_prime (S m)).
-elim Hcut.elim H1.
-cut (nth_prime a < p \lor nth_prime a = p).
-elim Hcut1.
-absurd (prime p).
-assumption.
-apply (lt_nth_prime_to_not_prime a).assumption.assumption.
-apply (ex_intro nat ? a).assumption.
-apply le_to_or_lt_eq.assumption.
-apply ex_m_le_n_nth_prime_m.
-simplify.unfold prime in H.elim H.assumption.
-qed.
-