src/HOL/NumberTheory/Quadratic_Reciprocity.thy
author nipkow
Thu Jul 07 12:39:17 2005 +0200 (2005-07-07)
changeset 16733 236dfafbeb63
parent 16663 13e9c402308b
child 18369 694ea14ab4f2
permissions -rw-r--r--
linear arithmetic now takes "&" in assumptions apart.
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(*  Title:      HOL/Quadratic_Reciprocity/Quadratic_Reciprocity.thy
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    ID:         $Id$
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    Authors:    Jeremy Avigad, David Gray, and Adam Kramer
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*)
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header {* The law of Quadratic reciprocity *}
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theory Quadratic_Reciprocity
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imports Gauss
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begin
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(***************************************************************)
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(*                                                             *)
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(*  Lemmas leading up to the proof of theorem 3.3 in           *)
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(*  Niven and Zuckerman's presentation                         *)
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(*                                                             *)
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(***************************************************************)
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lemma (in GAUSS) QRLemma1: "a * setsum id A = 
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  p * setsum (%x. ((x * a) div p)) A + setsum id D + setsum id E"
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proof -
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  from finite_A have "a * setsum id A = setsum (%x. a * x) A" 
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    by (auto simp add: setsum_const_mult id_def)
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  also have "setsum (%x. a * x) = setsum (%x. x * a)" 
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    by (auto simp add: zmult_commute)
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  also have "setsum (%x. x * a) A = setsum id B"
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    by (simp add: B_def setsum_reindex_id[OF inj_on_xa_A])
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  also have "... = setsum (%x. p * (x div p) + StandardRes p x) B"
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    by (auto simp add: StandardRes_def zmod_zdiv_equality)
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  also have "... = setsum (%x. p * (x div p)) B + setsum (StandardRes p) B"
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    by (rule setsum_addf)
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  also have "setsum (StandardRes p) B = setsum id C"
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    by (auto simp add: C_def setsum_reindex_id[OF SR_B_inj])
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  also from C_eq have "... = setsum id (D \<union> E)"
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    by auto
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  also from finite_D finite_E have "... = setsum id D + setsum id E"
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    apply (rule setsum_Un_disjoint)
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    by (auto simp add: D_def E_def)
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  also have "setsum (%x. p * (x div p)) B = 
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      setsum ((%x. p * (x div p)) o (%x. (x * a))) A"
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    by (auto simp add: B_def setsum_reindex inj_on_xa_A)
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  also have "... = setsum (%x. p * ((x * a) div p)) A"
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    by (auto simp add: o_def)
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  also from finite_A have "setsum (%x. p * ((x * a) div p)) A = 
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    p * setsum (%x. ((x * a) div p)) A"
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    by (auto simp add: setsum_const_mult)
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  finally show ?thesis by arith
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qed
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lemma (in GAUSS) QRLemma2: "setsum id A = p * int (card E) - setsum id E + 
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  setsum id D" 
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proof -
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  from F_Un_D_eq_A have "setsum id A = setsum id (D \<union> F)"
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    by (simp add: Un_commute)
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  also from F_D_disj finite_D finite_F have 
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      "... = setsum id D + setsum id F"
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    apply (simp add: Int_commute)
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    by (intro setsum_Un_disjoint) 
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  also from F_def have "F = (%x. (p - x)) ` E"
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    by auto
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  also from finite_E inj_on_pminusx_E have "setsum id ((%x. (p - x)) ` E) =
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      setsum (%x. (p - x)) E"
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    by (auto simp add: setsum_reindex)
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  also from finite_E have "setsum (op - p) E = setsum (%x. p) E - setsum id E"
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    by (auto simp add: setsum_subtractf id_def)
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  also from finite_E have "setsum (%x. p) E = p * int(card E)"
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    by (intro setsum_const)
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  finally show ?thesis
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    by arith
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qed
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lemma (in GAUSS) QRLemma3: "(a - 1) * setsum id A = 
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    p * (setsum (%x. ((x * a) div p)) A - int(card E)) + 2 * setsum id E"
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proof -
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  have "(a - 1) * setsum id A = a * setsum id A - setsum id A"
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    by (auto simp add: zdiff_zmult_distrib)  
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  also note QRLemma1
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  also from QRLemma2 have "p * (\<Sum>x \<in> A. x * a div p) + setsum id D + 
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     setsum id E - setsum id A = 
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      p * (\<Sum>x \<in> A. x * a div p) + setsum id D + 
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      setsum id E - (p * int (card E) - setsum id E + setsum id D)"
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    by auto
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  also have "... = p * (\<Sum>x \<in> A. x * a div p) - 
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      p * int (card E) + 2 * setsum id E" 
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    by arith
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  finally show ?thesis
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    by (auto simp only: zdiff_zmult_distrib2)
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qed
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lemma (in GAUSS) QRLemma4: "a \<in> zOdd ==> 
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    (setsum (%x. ((x * a) div p)) A \<in> zEven) = (int(card E): zEven)"
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proof -
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  assume a_odd: "a \<in> zOdd"
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  from QRLemma3 have a: "p * (setsum (%x. ((x * a) div p)) A - int(card E)) =
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      (a - 1) * setsum id A - 2 * setsum id E" 
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    by arith
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  from a_odd have "a - 1 \<in> zEven"
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    by (rule odd_minus_one_even)
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  hence "(a - 1) * setsum id A \<in> zEven"
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    by (rule even_times_either)
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  moreover have "2 * setsum id E \<in> zEven"
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    by (auto simp add: zEven_def)
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  ultimately have "(a - 1) * setsum id A - 2 * setsum id E \<in> zEven"
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    by (rule even_minus_even)
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  with a have "p * (setsum (%x. ((x * a) div p)) A - int(card E)): zEven"
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    by simp
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  hence "p \<in> zEven | (setsum (%x. ((x * a) div p)) A - int(card E)): zEven"
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    by (rule EvenOdd.even_product)
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  with p_odd have "(setsum (%x. ((x * a) div p)) A - int(card E)): zEven"
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    by (auto simp add: odd_iff_not_even)
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  thus ?thesis
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    by (auto simp only: even_diff [THEN sym])
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qed
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lemma (in GAUSS) QRLemma5: "a \<in> zOdd ==> 
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   (-1::int)^(card E) = (-1::int)^(nat(setsum (%x. ((x * a) div p)) A))"
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proof -
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  assume "a \<in> zOdd"
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  from QRLemma4 have
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    "(int(card E): zEven) = (setsum (%x. ((x * a) div p)) A \<in> zEven)"..
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  moreover have "0 \<le> int(card E)"
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    by auto
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  moreover have "0 \<le> setsum (%x. ((x * a) div p)) A"
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    proof (intro setsum_nonneg)
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      show "\<forall>x \<in> A. 0 \<le> x * a div p"
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      proof
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        fix x
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        assume "x \<in> A"
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        then have "0 \<le> x"
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          by (auto simp add: A_def)
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        with a_nonzero have "0 \<le> x * a"
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          by (auto simp add: zero_le_mult_iff)
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        with p_g_2 show "0 \<le> x * a div p" 
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          by (auto simp add: pos_imp_zdiv_nonneg_iff)
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      qed
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    qed
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  ultimately have "(-1::int)^nat((int (card E))) =
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      (-1)^nat(((\<Sum>x \<in> A. x * a div p)))"
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    by (intro neg_one_power_parity, auto)
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  also have "nat (int(card E)) = card E"
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    by auto
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  finally show ?thesis .
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qed
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lemma MainQRLemma: "[| a \<in> zOdd; 0 < a; ~([a = 0] (mod p)); zprime p; 2 < p;
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  A = {x. 0 < x & x \<le> (p - 1) div 2} |] ==> 
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  (Legendre a p) = (-1::int)^(nat(setsum (%x. ((x * a) div p)) A))"
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  apply (subst GAUSS.gauss_lemma)
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  apply (auto simp add: GAUSS_def)
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  apply (subst GAUSS.QRLemma5)
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by (auto simp add: GAUSS_def)
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(******************************************************************)
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(*                                                                *)
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(* Stuff about S, S1 and S2...                                    *)
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(*                                                                *)
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(******************************************************************)
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locale QRTEMP =
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  fixes p     :: "int"
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  fixes q     :: "int"
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  fixes P_set :: "int set"
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  fixes Q_set :: "int set"
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  fixes S     :: "(int * int) set"
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  fixes S1    :: "(int * int) set"
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  fixes S2    :: "(int * int) set"
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  fixes f1    :: "int => (int * int) set"
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  fixes f2    :: "int => (int * int) set"
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  assumes p_prime: "zprime p"
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  assumes p_g_2: "2 < p"
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  assumes q_prime: "zprime q"
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  assumes q_g_2: "2 < q"
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  assumes p_neq_q:      "p \<noteq> q"
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  defines P_set_def: "P_set == {x. 0 < x & x \<le> ((p - 1) div 2) }"
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  defines Q_set_def: "Q_set == {x. 0 < x & x \<le> ((q - 1) div 2) }"
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  defines S_def:     "S     == P_set <*> Q_set"
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  defines S1_def:    "S1    == { (x, y). (x, y):S & ((p * y) < (q * x)) }"
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  defines S2_def:    "S2    == { (x, y). (x, y):S & ((q * x) < (p * y)) }"
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  defines f1_def:    "f1 j  == { (j1, y). (j1, y):S & j1 = j & 
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                                 (y \<le> (q * j) div p) }"
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  defines f2_def:    "f2 j  == { (x, j1). (x, j1):S & j1 = j & 
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                                 (x \<le> (p * j) div q) }"
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lemma (in QRTEMP) p_fact: "0 < (p - 1) div 2"
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proof -
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  from prems have "2 < p" by (simp add: QRTEMP_def)
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  then have "2 \<le> p - 1" by arith
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  then have "2 div 2 \<le> (p - 1) div 2" by (rule zdiv_mono1, auto)
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  then show ?thesis by auto
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qed
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lemma (in QRTEMP) q_fact: "0 < (q - 1) div 2"
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proof -
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  from prems have "2 < q" by (simp add: QRTEMP_def)
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  then have "2 \<le> q - 1" by arith
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  then have "2 div 2 \<le> (q - 1) div 2" by (rule zdiv_mono1, auto)
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  then show ?thesis by auto
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qed
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lemma (in QRTEMP) pb_neq_qa: "[|1 \<le> b; b \<le> (q - 1) div 2 |] ==> 
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    (p * b \<noteq> q * a)"
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proof
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  assume "p * b = q * a" and "1 \<le> b" and "b \<le> (q - 1) div 2"
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  then have "q dvd (p * b)" by (auto simp add: dvd_def)
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  with q_prime p_g_2 have "q dvd p | q dvd b"
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    by (auto simp add: zprime_zdvd_zmult)
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  moreover have "~ (q dvd p)"
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  proof
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    assume "q dvd p"
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    with p_prime have "q = 1 | q = p"
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      apply (auto simp add: zprime_def QRTEMP_def)
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      apply (drule_tac x = q and R = False in allE)
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      apply (simp add: QRTEMP_def)    
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      apply (subgoal_tac "0 \<le> q", simp add: QRTEMP_def)
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      apply (insert prems)
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    by (auto simp add: QRTEMP_def)
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    with q_g_2 p_neq_q show False by auto
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  qed
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  ultimately have "q dvd b" by auto
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  then have "q \<le> b"
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  proof -
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    assume "q dvd b"
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    moreover from prems have "0 < b" by auto
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    ultimately show ?thesis by (insert zdvd_bounds [of q b], auto)
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  qed
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  with prems have "q \<le> (q - 1) div 2" by auto
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  then have "2 * q \<le> 2 * ((q - 1) div 2)" by arith
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  then have "2 * q \<le> q - 1"
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  proof -
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    assume "2 * q \<le> 2 * ((q - 1) div 2)"
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    with prems have "q \<in> zOdd" by (auto simp add: QRTEMP_def zprime_zOdd_eq_grt_2)
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    with odd_minus_one_even have "(q - 1):zEven" by auto
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    with even_div_2_prop2 have "(q - 1) = 2 * ((q - 1) div 2)" by auto
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    with prems show ?thesis by auto
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  qed
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  then have p1: "q \<le> -1" by arith
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  with q_g_2 show False by auto
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qed
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lemma (in QRTEMP) P_set_finite: "finite (P_set)"
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  by (insert p_fact, auto simp add: P_set_def bdd_int_set_l_le_finite)
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lemma (in QRTEMP) Q_set_finite: "finite (Q_set)"
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  by (insert q_fact, auto simp add: Q_set_def bdd_int_set_l_le_finite)
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lemma (in QRTEMP) S_finite: "finite S"
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  by (auto simp add: S_def  P_set_finite Q_set_finite finite_cartesian_product)
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lemma (in QRTEMP) S1_finite: "finite S1"
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proof -
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  have "finite S" by (auto simp add: S_finite)
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  moreover have "S1 \<subseteq> S" by (auto simp add: S1_def S_def)
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  ultimately show ?thesis by (auto simp add: finite_subset)
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qed
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lemma (in QRTEMP) S2_finite: "finite S2"
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proof -
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  have "finite S" by (auto simp add: S_finite)
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  moreover have "S2 \<subseteq> S" by (auto simp add: S2_def S_def)
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  ultimately show ?thesis by (auto simp add: finite_subset)
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qed
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lemma (in QRTEMP) P_set_card: "(p - 1) div 2 = int (card (P_set))"
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  by (insert p_fact, auto simp add: P_set_def card_bdd_int_set_l_le)
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lemma (in QRTEMP) Q_set_card: "(q - 1) div 2 = int (card (Q_set))"
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  by (insert q_fact, auto simp add: Q_set_def card_bdd_int_set_l_le)
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lemma (in QRTEMP) S_card: "((p - 1) div 2) * ((q - 1) div 2) = int (card(S))"
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  apply (insert P_set_card Q_set_card P_set_finite Q_set_finite)
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  apply (auto simp add: S_def zmult_int setsum_constant)
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done
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lemma (in QRTEMP) S1_Int_S2_prop: "S1 \<inter> S2 = {}"
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  by (auto simp add: S1_def S2_def)
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lemma (in QRTEMP) S1_Union_S2_prop: "S = S1 \<union> S2"
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  apply (auto simp add: S_def P_set_def Q_set_def S1_def S2_def)
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  proof -
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    fix a and b
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    assume "~ q * a < p * b" and b1: "0 < b" and b2: "b \<le> (q - 1) div 2"
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    with zless_linear have "(p * b < q * a) | (p * b = q * a)" by auto
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    moreover from pb_neq_qa b1 b2 have "(p * b \<noteq> q * a)" by auto
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    ultimately show "p * b < q * a" by auto
nipkow@15392
   287
  qed
paulson@13871
   288
paulson@13871
   289
lemma (in QRTEMP) card_sum_S1_S2: "((p - 1) div 2) * ((q - 1) div 2) = 
nipkow@15392
   290
    int(card(S1)) + int(card(S2))"
nipkow@15392
   291
proof-
nipkow@15392
   292
  have "((p - 1) div 2) * ((q - 1) div 2) = int (card(S))"
paulson@13871
   293
    by (auto simp add: S_card)
nipkow@15392
   294
  also have "... = int( card(S1) + card(S2))"
paulson@13871
   295
    apply (insert S1_finite S2_finite S1_Int_S2_prop S1_Union_S2_prop)
paulson@13871
   296
    apply (drule card_Un_disjoint, auto)
paulson@13871
   297
  done
paulson@13871
   298
  also have "... = int(card(S1)) + int(card(S2))" by auto
nipkow@15392
   299
  finally show ?thesis .
nipkow@15392
   300
qed
paulson@13871
   301
paulson@13871
   302
lemma (in QRTEMP) aux1a: "[| 0 < a; a \<le> (p - 1) div 2; 
paulson@13871
   303
                             0 < b; b \<le> (q - 1) div 2 |] ==>
nipkow@15392
   304
                          (p * b < q * a) = (b \<le> q * a div p)"
nipkow@15392
   305
proof -
nipkow@15392
   306
  assume "0 < a" and "a \<le> (p - 1) div 2" and "0 < b" and "b \<le> (q - 1) div 2"
nipkow@15392
   307
  have "p * b < q * a ==> b \<le> q * a div p"
nipkow@15392
   308
  proof -
nipkow@15392
   309
    assume "p * b < q * a"
paulson@13871
   310
    then have "p * b \<le> q * a" by auto
nipkow@15392
   311
    then have "(p * b) div p \<le> (q * a) div p"
paulson@13871
   312
      by (rule zdiv_mono1, insert p_g_2, auto)
nipkow@15392
   313
    then show "b \<le> (q * a) div p"
paulson@13871
   314
      apply (subgoal_tac "p \<noteq> 0")
paulson@13871
   315
      apply (frule zdiv_zmult_self2, force)
paulson@13871
   316
      by (insert p_g_2, auto)
nipkow@15392
   317
  qed
nipkow@15392
   318
  moreover have "b \<le> q * a div p ==> p * b < q * a"
nipkow@15392
   319
  proof -
nipkow@15392
   320
    assume "b \<le> q * a div p"
nipkow@15392
   321
    then have "p * b \<le> p * ((q * a) div p)"
paulson@14387
   322
      by (insert p_g_2, auto simp add: mult_le_cancel_left)
nipkow@15392
   323
    also have "... \<le> q * a"
paulson@13871
   324
      by (rule zdiv_leq_prop, insert p_g_2, auto)
nipkow@15392
   325
    finally have "p * b \<le> q * a" .
nipkow@15392
   326
    then have "p * b < q * a | p * b = q * a"
paulson@13871
   327
      by (simp only: order_le_imp_less_or_eq)
nipkow@15392
   328
    moreover have "p * b \<noteq> q * a"
paulson@13871
   329
      by (rule  pb_neq_qa, insert prems, auto)
paulson@13871
   330
    ultimately show ?thesis by auto
nipkow@15392
   331
  qed
nipkow@15392
   332
  ultimately show ?thesis ..
nipkow@15392
   333
qed
paulson@13871
   334
paulson@13871
   335
lemma (in QRTEMP) aux1b: "[| 0 < a; a \<le> (p - 1) div 2; 
paulson@13871
   336
                             0 < b; b \<le> (q - 1) div 2 |] ==>
nipkow@15392
   337
                          (q * a < p * b) = (a \<le> p * b div q)"
nipkow@15392
   338
proof -
nipkow@15392
   339
  assume "0 < a" and "a \<le> (p - 1) div 2" and "0 < b" and "b \<le> (q - 1) div 2"
nipkow@15392
   340
  have "q * a < p * b ==> a \<le> p * b div q"
nipkow@15392
   341
  proof -
nipkow@15392
   342
    assume "q * a < p * b"
paulson@13871
   343
    then have "q * a \<le> p * b" by auto
nipkow@15392
   344
    then have "(q * a) div q \<le> (p * b) div q"
paulson@13871
   345
      by (rule zdiv_mono1, insert q_g_2, auto)
nipkow@15392
   346
    then show "a \<le> (p * b) div q"
paulson@13871
   347
      apply (subgoal_tac "q \<noteq> 0")
paulson@13871
   348
      apply (frule zdiv_zmult_self2, force)
paulson@13871
   349
      by (insert q_g_2, auto)
nipkow@15392
   350
  qed
nipkow@15392
   351
  moreover have "a \<le> p * b div q ==> q * a < p * b"
nipkow@15392
   352
  proof -
nipkow@15392
   353
    assume "a \<le> p * b div q"
nipkow@15392
   354
    then have "q * a \<le> q * ((p * b) div q)"
paulson@14387
   355
      by (insert q_g_2, auto simp add: mult_le_cancel_left)
nipkow@15392
   356
    also have "... \<le> p * b"
paulson@13871
   357
      by (rule zdiv_leq_prop, insert q_g_2, auto)
nipkow@15392
   358
    finally have "q * a \<le> p * b" .
nipkow@15392
   359
    then have "q * a < p * b | q * a = p * b"
paulson@13871
   360
      by (simp only: order_le_imp_less_or_eq)
nipkow@15392
   361
    moreover have "p * b \<noteq> q * a"
paulson@13871
   362
      by (rule  pb_neq_qa, insert prems, auto)
paulson@13871
   363
    ultimately show ?thesis by auto
nipkow@15392
   364
  qed
nipkow@15392
   365
  ultimately show ?thesis ..
nipkow@15392
   366
qed
paulson@13871
   367
nipkow@16663
   368
lemma aux2: "[| zprime p; zprime q; 2 < p; 2 < q |] ==> 
nipkow@15392
   369
             (q * ((p - 1) div 2)) div p \<le> (q - 1) div 2"
nipkow@15392
   370
proof-
nipkow@16663
   371
  assume "zprime p" and "zprime q" and "2 < p" and "2 < q"
paulson@13871
   372
  (* Set up what's even and odd *)
nipkow@15392
   373
  then have "p \<in> zOdd & q \<in> zOdd"
paulson@13871
   374
    by (auto simp add:  zprime_zOdd_eq_grt_2)
nipkow@15392
   375
  then have even1: "(p - 1):zEven & (q - 1):zEven"
paulson@13871
   376
    by (auto simp add: odd_minus_one_even)
nipkow@15392
   377
  then have even2: "(2 * p):zEven & ((q - 1) * p):zEven"
paulson@13871
   378
    by (auto simp add: zEven_def)
nipkow@15392
   379
  then have even3: "(((q - 1) * p) + (2 * p)):zEven"
paulson@14434
   380
    by (auto simp: EvenOdd.even_plus_even)
paulson@13871
   381
  (* using these prove it *)
nipkow@15392
   382
  from prems have "q * (p - 1) < ((q - 1) * p) + (2 * p)"
paulson@13871
   383
    by (auto simp add: int_distrib)
nipkow@15392
   384
  then have "((p - 1) * q) div 2 < (((q - 1) * p) + (2 * p)) div 2"
nipkow@15392
   385
    apply (rule_tac x = "((p - 1) * q)" in even_div_2_l)
paulson@13871
   386
    by (auto simp add: even3, auto simp add: zmult_ac)
nipkow@15392
   387
  also have "((p - 1) * q) div 2 = q * ((p - 1) div 2)"
paulson@13871
   388
    by (auto simp add: even1 even_prod_div_2)
nipkow@15392
   389
  also have "(((q - 1) * p) + (2 * p)) div 2 = (((q - 1) div 2) * p) + p"
paulson@13871
   390
    by (auto simp add: even1 even2 even_prod_div_2 even_sum_div_2)
paulson@13871
   391
  finally show ?thesis 
paulson@13871
   392
    apply (rule_tac x = " q * ((p - 1) div 2)" and 
nipkow@15392
   393
                    y = "(q - 1) div 2" in div_prop2)
paulson@13871
   394
    by (insert prems, auto)
nipkow@15392
   395
qed
paulson@13871
   396
nipkow@15392
   397
lemma (in QRTEMP) aux3a: "\<forall>j \<in> P_set. int (card (f1 j)) = (q * j) div p"
nipkow@15392
   398
proof
nipkow@15392
   399
  fix j
nipkow@15392
   400
  assume j_fact: "j \<in> P_set"
nipkow@15392
   401
  have "int (card (f1 j)) = int (card {y. y \<in> Q_set & y \<le> (q * j) div p})"
nipkow@15392
   402
  proof -
nipkow@15392
   403
    have "finite (f1 j)"
nipkow@15392
   404
    proof -
paulson@13871
   405
      have "(f1 j) \<subseteq> S" by (auto simp add: f1_def)
paulson@13871
   406
      with S_finite show ?thesis by (auto simp add: finite_subset)
nipkow@15392
   407
    qed
nipkow@15392
   408
    moreover have "inj_on (%(x,y). y) (f1 j)"
paulson@13871
   409
      by (auto simp add: f1_def inj_on_def)
nipkow@15392
   410
    ultimately have "card ((%(x,y). y) ` (f1 j)) = card  (f1 j)"
paulson@13871
   411
      by (auto simp add: f1_def card_image)
nipkow@15392
   412
    moreover have "((%(x,y). y) ` (f1 j)) = {y. y \<in> Q_set & y \<le> (q * j) div p}"
paulson@13871
   413
      by (insert prems, auto simp add: f1_def S_def Q_set_def P_set_def 
paulson@13871
   414
        image_def)
paulson@13871
   415
    ultimately show ?thesis by (auto simp add: f1_def)
nipkow@15392
   416
  qed
nipkow@15392
   417
  also have "... = int (card {y. 0 < y & y \<le> (q * j) div p})"
nipkow@15392
   418
  proof -
paulson@13871
   419
    have "{y. y \<in> Q_set & y \<le> (q * j) div p} = 
nipkow@15392
   420
        {y. 0 < y & y \<le> (q * j) div p}"
paulson@13871
   421
      apply (auto simp add: Q_set_def)
nipkow@15392
   422
      proof -
nipkow@15392
   423
        fix x
nipkow@15392
   424
        assume "0 < x" and "x \<le> q * j div p"
nipkow@15392
   425
        with j_fact P_set_def  have "j \<le> (p - 1) div 2" by auto
nipkow@15392
   426
        with q_g_2 have "q * j \<le> q * ((p - 1) div 2)"
paulson@14387
   427
          by (auto simp add: mult_le_cancel_left)
nipkow@15392
   428
        with p_g_2 have "q * j div p \<le> q * ((p - 1) div 2) div p"
paulson@13871
   429
          by (auto simp add: zdiv_mono1)
nipkow@15392
   430
        also from prems have "... \<le> (q - 1) div 2"
paulson@13871
   431
          apply simp apply (insert aux2) by (simp add: QRTEMP_def)
paulson@13871
   432
        finally show "x \<le> (q - 1) div 2" by (insert prems, auto)
nipkow@15392
   433
      qed
paulson@13871
   434
    then show ?thesis by auto
nipkow@15392
   435
  qed
nipkow@15392
   436
  also have "... = (q * j) div p"
nipkow@15392
   437
  proof -
paulson@13871
   438
    from j_fact P_set_def have "0 \<le> j" by auto
paulson@14387
   439
    with q_g_2 have "q * 0 \<le> q * j" by (auto simp only: mult_left_mono)
paulson@13871
   440
    then have "0 \<le> q * j" by auto
nipkow@15392
   441
    then have "0 div p \<le> (q * j) div p"
paulson@13871
   442
      apply (rule_tac a = 0 in zdiv_mono1)
paulson@13871
   443
      by (insert p_g_2, auto)
paulson@13871
   444
    also have "0 div p = 0" by auto
paulson@13871
   445
    finally show ?thesis by (auto simp add: card_bdd_int_set_l_le)
nipkow@15392
   446
  qed
nipkow@15392
   447
  finally show "int (card (f1 j)) = q * j div p" .
nipkow@15392
   448
qed
paulson@13871
   449
nipkow@15392
   450
lemma (in QRTEMP) aux3b: "\<forall>j \<in> Q_set. int (card (f2 j)) = (p * j) div q"
nipkow@15392
   451
proof
nipkow@15392
   452
  fix j
nipkow@15392
   453
  assume j_fact: "j \<in> Q_set"
nipkow@15392
   454
  have "int (card (f2 j)) = int (card {y. y \<in> P_set & y \<le> (p * j) div q})"
nipkow@15392
   455
  proof -
nipkow@15392
   456
    have "finite (f2 j)"
nipkow@15392
   457
    proof -
paulson@13871
   458
      have "(f2 j) \<subseteq> S" by (auto simp add: f2_def)
paulson@13871
   459
      with S_finite show ?thesis by (auto simp add: finite_subset)
nipkow@15392
   460
    qed
nipkow@15392
   461
    moreover have "inj_on (%(x,y). x) (f2 j)"
paulson@13871
   462
      by (auto simp add: f2_def inj_on_def)
nipkow@15392
   463
    ultimately have "card ((%(x,y). x) ` (f2 j)) = card  (f2 j)"
paulson@13871
   464
      by (auto simp add: f2_def card_image)
nipkow@15392
   465
    moreover have "((%(x,y). x) ` (f2 j)) = {y. y \<in> P_set & y \<le> (p * j) div q}"
paulson@13871
   466
      by (insert prems, auto simp add: f2_def S_def Q_set_def 
paulson@13871
   467
        P_set_def image_def)
paulson@13871
   468
    ultimately show ?thesis by (auto simp add: f2_def)
nipkow@15392
   469
  qed
nipkow@15392
   470
  also have "... = int (card {y. 0 < y & y \<le> (p * j) div q})"
nipkow@15392
   471
  proof -
paulson@13871
   472
    have "{y. y \<in> P_set & y \<le> (p * j) div q} = 
nipkow@15392
   473
        {y. 0 < y & y \<le> (p * j) div q}"
paulson@13871
   474
      apply (auto simp add: P_set_def)
nipkow@15392
   475
      proof -
nipkow@15392
   476
        fix x
nipkow@15392
   477
        assume "0 < x" and "x \<le> p * j div q"
nipkow@15392
   478
        with j_fact Q_set_def  have "j \<le> (q - 1) div 2" by auto
nipkow@15392
   479
        with p_g_2 have "p * j \<le> p * ((q - 1) div 2)"
paulson@14387
   480
          by (auto simp add: mult_le_cancel_left)
nipkow@15392
   481
        with q_g_2 have "p * j div q \<le> p * ((q - 1) div 2) div q"
paulson@13871
   482
          by (auto simp add: zdiv_mono1)
nipkow@15392
   483
        also from prems have "... \<le> (p - 1) div 2"
paulson@13871
   484
          by (auto simp add: aux2 QRTEMP_def)
paulson@13871
   485
        finally show "x \<le> (p - 1) div 2" by (insert prems, auto)
nipkow@15392
   486
      qed
paulson@13871
   487
    then show ?thesis by auto
nipkow@15392
   488
  qed
nipkow@15392
   489
  also have "... = (p * j) div q"
nipkow@15392
   490
  proof -
paulson@13871
   491
    from j_fact Q_set_def have "0 \<le> j" by auto
paulson@14387
   492
    with p_g_2 have "p * 0 \<le> p * j" by (auto simp only: mult_left_mono)
paulson@13871
   493
    then have "0 \<le> p * j" by auto
nipkow@15392
   494
    then have "0 div q \<le> (p * j) div q"
paulson@13871
   495
      apply (rule_tac a = 0 in zdiv_mono1)
paulson@13871
   496
      by (insert q_g_2, auto)
paulson@13871
   497
    also have "0 div q = 0" by auto
paulson@13871
   498
    finally show ?thesis by (auto simp add: card_bdd_int_set_l_le)
nipkow@15392
   499
  qed
nipkow@15392
   500
  finally show "int (card (f2 j)) = p * j div q" .
nipkow@15392
   501
qed
paulson@13871
   502
nipkow@15392
   503
lemma (in QRTEMP) S1_card: "int (card(S1)) = setsum (%j. (q * j) div p) P_set"
nipkow@15392
   504
proof -
nipkow@15392
   505
  have "\<forall>x \<in> P_set. finite (f1 x)"
nipkow@15392
   506
  proof
nipkow@15392
   507
    fix x
paulson@13871
   508
    have "f1 x \<subseteq> S" by (auto simp add: f1_def)
paulson@13871
   509
    with S_finite show "finite (f1 x)" by (auto simp add: finite_subset)
nipkow@15392
   510
  qed
nipkow@15392
   511
  moreover have "(\<forall>x \<in> P_set. \<forall>y \<in> P_set. x \<noteq> y --> (f1 x) \<inter> (f1 y) = {})"
paulson@13871
   512
    by (auto simp add: f1_def)
nipkow@15392
   513
  moreover note P_set_finite
paulson@13871
   514
  ultimately have "int(card (UNION P_set f1)) = 
nipkow@15392
   515
      setsum (%x. int(card (f1 x))) P_set"
nipkow@15402
   516
    by(simp add:card_UN_disjoint int_setsum o_def)
nipkow@15392
   517
  moreover have "S1 = UNION P_set f1"
paulson@13871
   518
    by (auto simp add: f1_def S_def S1_def S2_def P_set_def Q_set_def aux1a)
paulson@13871
   519
  ultimately have "int(card (S1)) = setsum (%j. int(card (f1 j))) P_set" 
paulson@13871
   520
    by auto
nipkow@15392
   521
  also have "... = setsum (%j. q * j div p) P_set"
nipkow@15392
   522
    using aux3a by(fastsimp intro: setsum_cong)
nipkow@15392
   523
  finally show ?thesis .
nipkow@15392
   524
qed
paulson@13871
   525
nipkow@15392
   526
lemma (in QRTEMP) S2_card: "int (card(S2)) = setsum (%j. (p * j) div q) Q_set"
nipkow@15392
   527
proof -
nipkow@15392
   528
  have "\<forall>x \<in> Q_set. finite (f2 x)"
nipkow@15392
   529
  proof
nipkow@15392
   530
    fix x
paulson@13871
   531
    have "f2 x \<subseteq> S" by (auto simp add: f2_def)
paulson@13871
   532
    with S_finite show "finite (f2 x)" by (auto simp add: finite_subset)
nipkow@15392
   533
  qed
paulson@13871
   534
  moreover have "(\<forall>x \<in> Q_set. \<forall>y \<in> Q_set. x \<noteq> y --> 
nipkow@15392
   535
      (f2 x) \<inter> (f2 y) = {})"
paulson@13871
   536
    by (auto simp add: f2_def)
nipkow@15392
   537
  moreover note Q_set_finite
paulson@13871
   538
  ultimately have "int(card (UNION Q_set f2)) = 
nipkow@15392
   539
      setsum (%x. int(card (f2 x))) Q_set"
nipkow@15402
   540
    by(simp add:card_UN_disjoint int_setsum o_def)
nipkow@15392
   541
  moreover have "S2 = UNION Q_set f2"
paulson@13871
   542
    by (auto simp add: f2_def S_def S1_def S2_def P_set_def Q_set_def aux1b)
paulson@13871
   543
  ultimately have "int(card (S2)) = setsum (%j. int(card (f2 j))) Q_set" 
paulson@13871
   544
    by auto
nipkow@15392
   545
  also have "... = setsum (%j. p * j div q) Q_set"
nipkow@15392
   546
    using aux3b by(fastsimp intro: setsum_cong)
nipkow@15392
   547
  finally show ?thesis .
nipkow@15392
   548
qed
paulson@13871
   549
paulson@13871
   550
lemma (in QRTEMP) S1_carda: "int (card(S1)) = 
nipkow@15392
   551
    setsum (%j. (j * q) div p) P_set"
paulson@13871
   552
  by (auto simp add: S1_card zmult_ac)
paulson@13871
   553
paulson@13871
   554
lemma (in QRTEMP) S2_carda: "int (card(S2)) = 
nipkow@15392
   555
    setsum (%j. (j * p) div q) Q_set"
paulson@13871
   556
  by (auto simp add: S2_card zmult_ac)
paulson@13871
   557
paulson@13871
   558
lemma (in QRTEMP) pq_sum_prop: "(setsum (%j. (j * p) div q) Q_set) + 
nipkow@15392
   559
    (setsum (%j. (j * q) div p) P_set) = ((p - 1) div 2) * ((q - 1) div 2)"
nipkow@15392
   560
proof -
paulson@13871
   561
  have "(setsum (%j. (j * p) div q) Q_set) + 
nipkow@15392
   562
      (setsum (%j. (j * q) div p) P_set) = int (card S2) + int (card S1)"
paulson@13871
   563
    by (auto simp add: S1_carda S2_carda)
nipkow@15392
   564
  also have "... = int (card S1) + int (card S2)"
paulson@13871
   565
    by auto
nipkow@15392
   566
  also have "... = ((p - 1) div 2) * ((q - 1) div 2)"
paulson@13871
   567
    by (auto simp add: card_sum_S1_S2)
nipkow@15392
   568
  finally show ?thesis .
nipkow@15392
   569
qed
paulson@13871
   570
nipkow@16663
   571
lemma pq_prime_neq: "[| zprime p; zprime q; p \<noteq> q |] ==> (~[p = 0] (mod q))"
paulson@13871
   572
  apply (auto simp add: zcong_eq_zdvd_prop zprime_def)
paulson@13871
   573
  apply (drule_tac x = q in allE)
paulson@13871
   574
  apply (drule_tac x = p in allE)
paulson@13871
   575
by auto
paulson@13871
   576
paulson@13871
   577
lemma (in QRTEMP) QR_short: "(Legendre p q) * (Legendre q p) = 
nipkow@15392
   578
    (-1::int)^nat(((p - 1) div 2)*((q - 1) div 2))"
nipkow@15392
   579
proof -
nipkow@15392
   580
  from prems have "~([p = 0] (mod q))"
paulson@13871
   581
    by (auto simp add: pq_prime_neq QRTEMP_def)
paulson@13871
   582
  with prems have a1: "(Legendre p q) = (-1::int) ^ 
nipkow@15392
   583
      nat(setsum (%x. ((x * p) div q)) Q_set)"
paulson@13871
   584
    apply (rule_tac p = q in  MainQRLemma)
paulson@13871
   585
    by (auto simp add: zprime_zOdd_eq_grt_2 QRTEMP_def)
nipkow@15392
   586
  from prems have "~([q = 0] (mod p))"
paulson@13871
   587
    apply (rule_tac p = q and q = p in pq_prime_neq)
nipkow@15392
   588
    apply (simp add: QRTEMP_def)+
nipkow@16733
   589
    done
paulson@13871
   590
  with prems have a2: "(Legendre q p) = 
nipkow@15392
   591
      (-1::int) ^ nat(setsum (%x. ((x * q) div p)) P_set)"
paulson@13871
   592
    apply (rule_tac p = p in  MainQRLemma)
paulson@13871
   593
    by (auto simp add: zprime_zOdd_eq_grt_2 QRTEMP_def)
paulson@13871
   594
  from a1 a2 have "(Legendre p q) * (Legendre q p) = 
paulson@13871
   595
      (-1::int) ^ nat(setsum (%x. ((x * p) div q)) Q_set) *
nipkow@15392
   596
        (-1::int) ^ nat(setsum (%x. ((x * q) div p)) P_set)"
paulson@13871
   597
    by auto
paulson@13871
   598
  also have "... = (-1::int) ^ (nat(setsum (%x. ((x * p) div q)) Q_set) + 
nipkow@15392
   599
                   nat(setsum (%x. ((x * q) div p)) P_set))"
paulson@13871
   600
    by (auto simp add: zpower_zadd_distrib)
paulson@13871
   601
  also have "nat(setsum (%x. ((x * p) div q)) Q_set) + 
paulson@13871
   602
      nat(setsum (%x. ((x * q) div p)) P_set) =
paulson@13871
   603
        nat((setsum (%x. ((x * p) div q)) Q_set) + 
nipkow@15392
   604
          (setsum (%x. ((x * q) div p)) P_set))"
paulson@13871
   605
    apply (rule_tac z1 = "setsum (%x. ((x * p) div q)) Q_set" in 
nipkow@15392
   606
      nat_add_distrib [THEN sym])
paulson@13871
   607
    by (auto simp add: S1_carda [THEN sym] S2_carda [THEN sym])
nipkow@15392
   608
  also have "... = nat(((p - 1) div 2) * ((q - 1) div 2))"
paulson@13871
   609
    by (auto simp add: pq_sum_prop)
nipkow@15392
   610
  finally show ?thesis .
nipkow@15392
   611
qed
paulson@13871
   612
paulson@13871
   613
theorem Quadratic_Reciprocity:
nipkow@16663
   614
     "[| p \<in> zOdd; zprime p; q \<in> zOdd; zprime q; 
paulson@13871
   615
         p \<noteq> q |] 
paulson@13871
   616
      ==> (Legendre p q) * (Legendre q p) = 
nipkow@15392
   617
          (-1::int)^nat(((p - 1) div 2)*((q - 1) div 2))"
paulson@13871
   618
  by (auto simp add: QRTEMP.QR_short zprime_zOdd_eq_grt_2 [THEN sym] 
paulson@13871
   619
                     QRTEMP_def)
paulson@13871
   620
paulson@13871
   621
end