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-
-(*************************************************************)
-(* This file is distributed under the terms of the *)
-(* GNU Lesser General Public License Version 2.1 *)
-(*************************************************************)
-(* Benjamin.Gregoire@inria.fr Laurent.Thery@inria.fr *)
-(*************************************************************)
-
-(**********************************************************************
- Pepin.v
-
- Pepin's Test for Fermat Number
-
- Definition: PepinTest
- **********************************************************************)
-Require Import ZArith.
-Require Import ZCAux.
-Require Import Pocklington.
-
-Open Scope Z_scope.
-
-Definition FermatNumber n := 2^(2^(Z_of_nat n)) + 1.
-
-Theorem Fermat_pos: forall n, 1 < FermatNumber n.
-unfold FermatNumber; intros n; apply Zle_lt_trans with (2 ^ 2 ^(Z_of_nat n)); auto with zarith.
-rewrite <- (Zpower_0_r 2); auto with zarith.
-apply Zpower_le_monotone; try split; auto with zarith.
-Qed.
-
-Theorem PepinTest: forall n, let Fn := FermatNumber n in (3 ^ ((Fn - 1) / 2) + 1) mod Fn = 0 -> prime Fn.
-intros n Fn H.
-assert (Hn: 1 < Fn).
-unfold Fn; apply Fermat_pos.
-apply PocklingtonCorollary1 with (F1 := 2^(2^(Z_of_nat n))) (R1 := 1); auto with zarith.
-2: unfold Fn, FermatNumber; auto with zarith.
-apply Zlt_le_trans with (2 ^ 1); auto with zarith.
-rewrite Zpower_1_r; auto with zarith.
-apply Zpower_le_monotone; try split; auto with zarith.
-rewrite <- (Zpower_0_r 2); apply Zpower_le_monotone; try split; auto with zarith.
-unfold Fn, FermatNumber.
-assert (H1: 2 <= 2 ^ 2 ^ Z_of_nat n).
-pattern 2 at 1; rewrite <- (Zpower_1_r 2); auto with zarith.
-apply Zpower_le_monotone; split; auto with zarith.
-rewrite <- (Zpower_0_r 2); apply Zpower_le_monotone; try split; auto with zarith.
-apply Zlt_le_trans with (2 * 2 ^2 ^Z_of_nat n).
-assert (tmp: forall p, 2 * p = p + p); auto with zarith.
-apply Zmult_le_compat_r; auto with zarith.
-assert (Hd: (2 | Fn - 1)).
-exists (2 ^ (2^(Z_of_nat n) - 1)).
-pattern 2 at 3; rewrite <- (Zpower_1_r 2).
-rewrite <- Zpower_exp; auto with zarith.
-assert (tmp: forall p, p = (p - 1) +1); auto with zarith; rewrite <- tmp.
-unfold Fn, FermatNumber; ring.
-assert (0 < 2 ^ Z_of_nat n); auto with zarith.
-intros p Hp Hp1; exists 3; split; auto with zarith; split; auto.
-rewrite (Zdivide_Zdiv_eq 2 (Fn -1)); auto with zarith.
-rewrite Zmult_comm; rewrite Zpower_mult; auto with zarith.
-rewrite Zpower_mod; auto with zarith.
-assert (tmp: forall p, p = (p + 1) -1); auto with zarith; rewrite (fun x => (tmp (3 ^ x))).
-rewrite Zminus_mod; auto with zarith.
-rewrite H.
-rewrite (Zmod_small 1); auto with zarith.
-rewrite <- Zpower_mod; auto with zarith.
-rewrite Zmod_small; auto with zarith.
-simpl; unfold Zpower_pos; simpl; auto with zarith.
-apply Z_div_pos; auto with zarith.
-apply Zis_gcd_gcd; auto with zarith.
-apply Zis_gcd_intro; auto with zarith.
-intros x HD1 HD2.
-assert (Hd1: p = 2).
-apply prime_div_Zpower_prime with (4 := Hp1); auto with zarith.
-apply prime_2.
-assert (Hd2: (x | 2)).
-replace 2 with ((3 ^ ((Fn - 1) / 2) + 1) - (3 ^ ((Fn - 1) / 2) - 1)); auto with zarith.
-apply Zdivide_minus_l; auto.
-apply Zdivide_trans with (1 := HD2).
-apply Zmod_divide; auto with zarith.
-rewrite <- Hd1; auto.
-replace 1 with (Fn - (Fn - 1)); auto with zarith.
-apply Zdivide_minus_l; auto.
-apply Zdivide_trans with (1 := Hd2); auto.
-Qed.
-
-(* An optimized version with Zpow_mod *)
-
-Definition pepin_test n :=
- let Fn := FermatNumber n in if Z_eq_dec (Zpow_mod 3 ((Fn - 1) / 2) Fn) (Fn - 1) then true else false.
-
-Theorem PepinTestOp: forall n, pepin_test n = true -> prime (FermatNumber n).
-intros n; unfold pepin_test.
-match goal with |- context[if ?X then _ else _] => case X end; try (intros; discriminate).
-intros H1 _; apply PepinTest.
-generalize (Fermat_pos n); intros H2.
-rewrite Zplus_mod; auto with zarith.
-rewrite <- Zpow_mod_Zpower_correct; auto with zarith.
-rewrite H1.
-rewrite (Zmod_small 1); auto with zarith.
-replace (FermatNumber n - 1 + 1) with (FermatNumber n); auto with zarith.
-apply Zdivide_mod; auto with zarith.
-apply Z_div_pos; auto with zarith.
-Qed.
-
-Theorem prime5: prime 5.
-exact (PepinTestOp 1 (refl_equal _)).
-Qed.
-
-Theorem prime17: prime 17.
-exact (PepinTestOp 2 (refl_equal _)).
-Qed.
-
-Theorem prime257: prime 257.
-exact (PepinTestOp 3 (refl_equal _)).
-Qed.
-
-Theorem prime65537: prime 65537.
-exact (PepinTestOp 4 (refl_equal _)).
-Qed.
-
-(* Too tough !!
-Theorem prime4294967297: prime 4294967297.
-refine (PepinTestOp 5 (refl_equal _)).
-Qed.
-*)