src/HOL/Old_Number_Theory/Quadratic_Reciprocity.thy
author wenzelm
Sat Oct 10 16:26:23 2015 +0200 (2015-10-10)
changeset 61382 efac889fccbc
parent 58889 5b7a9633cfa8
child 61609 77b453bd616f
permissions -rw-r--r--
isabelle update_cartouches;
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(*  Title:      HOL/Old_Number_Theory/Quadratic_Reciprocity.thy
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    Authors:    Jeremy Avigad, David Gray, and Adam Kramer
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*)
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section \<open>The law of Quadratic reciprocity\<close>
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theory Quadratic_Reciprocity
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imports Gauss
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begin
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text \<open>
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  Lemmas leading up to the proof of theorem 3.3 in Niven and
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  Zuckerman's presentation.
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\<close>
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context GAUSS
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begin
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lemma 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: mult.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 [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.distrib)
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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 [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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    by (rule setsum.union_disjoint) (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 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
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  have "... = setsum id D + setsum id F"
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    by (auto simp add: Int_commute intro: setsum.union_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 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: left_diff_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: right_diff_distrib)
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qed
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lemma 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 [symmetric])
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qed
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lemma 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 [OF this] 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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end
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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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  apply (auto simp add: GAUSS_def)
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  apply (simp add: GAUSS.A_def [OF GAUSS.intro] GAUSS_def)
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  done
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subsection \<open>Stuff about S, S1 and S2\<close>
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locale QRTEMP =
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  fixes p     :: "int"
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  fixes q     :: "int"
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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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begin
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definition P_set :: "int set"
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  where "P_set = {x. 0 < x & x \<le> ((p - 1) div 2) }"
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definition Q_set :: "int set"
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  where "Q_set = {x. 0 < x & x \<le> ((q - 1) div 2) }"
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definition S :: "(int * int) set"
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  where "S = P_set <*> Q_set"
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definition S1 :: "(int * int) set"
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  where "S1 = { (x, y). (x, y):S & ((p * y) < (q * x)) }"
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definition S2 :: "(int * int) set"
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  where "S2 = { (x, y). (x, y):S & ((q * x) < (p * y)) }"
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definition f1 :: "int => (int * int) set"
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  where "f1 j = { (j1, y). (j1, y):S & j1 = j & (y \<le> (q * j) div p) }"
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definition f2 :: "int => (int * int) set"
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  where "f2 j = { (x, j1). (x, j1):S & j1 = j & (x \<le> (p * j) div q) }"
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lemma p_fact: "0 < (p - 1) div 2"
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proof -
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  from p_g_2 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 q_fact: "0 < (q - 1) div 2"
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proof -
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  from q_g_2 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 pb_neq_qa:
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  assumes "1 \<le> b" and "b \<le> (q - 1) div 2"
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  shows "p * b \<noteq> q * a"
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proof
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  assume "p * b = q * a"
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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 assms)
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      apply (auto simp add: QRTEMP_def)
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      done
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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 assms have "0 < b" by auto
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    ultimately show ?thesis using zdvd_bounds [of q b] by auto
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  qed
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  with assms 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 a: "2 * q \<le> 2 * ((q - 1) div 2)"
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    with assms 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 a 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 P_set_finite: "finite (P_set)"
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  using p_fact by (auto simp add: P_set_def bdd_int_set_l_le_finite)
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lemma Q_set_finite: "finite (Q_set)"
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  using q_fact by (auto simp add: Q_set_def bdd_int_set_l_le_finite)
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lemma 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 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 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 P_set_card: "(p - 1) div 2 = int (card (P_set))"
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  using p_fact by (auto simp add: P_set_def card_bdd_int_set_l_le)
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lemma Q_set_card: "(q - 1) div 2 = int (card (Q_set))"
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  using q_fact by (auto simp add: Q_set_def card_bdd_int_set_l_le)
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lemma S_card: "((p - 1) div 2) * ((q - 1) div 2) = int (card(S))"
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  using P_set_card Q_set_card P_set_finite Q_set_finite
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  by (auto simp add: S_def zmult_int)
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lemma S1_Int_S2_prop: "S1 \<inter> S2 = {}"
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  by (auto simp add: S1_def S2_def)
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lemma 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 less_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
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qed
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lemma card_sum_S1_S2: "((p - 1) div 2) * ((q - 1) div 2) =
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    int(card(S1)) + int(card(S2))"
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proof -
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  have "((p - 1) div 2) * ((q - 1) div 2) = int (card(S))"
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    by (auto simp add: S_card)
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  also have "... = int( card(S1) + card(S2))"
paulson@13871
   298
    apply (insert S1_finite S2_finite S1_Int_S2_prop S1_Union_S2_prop)
paulson@13871
   299
    apply (drule card_Un_disjoint, auto)
wenzelm@18369
   300
    done
paulson@13871
   301
  also have "... = int(card(S1)) + int(card(S2))" by auto
nipkow@15392
   302
  finally show ?thesis .
nipkow@15392
   303
qed
paulson@13871
   304
wenzelm@41541
   305
lemma aux1a:
wenzelm@41541
   306
  assumes "0 < a" and "a \<le> (p - 1) div 2"
wenzelm@41541
   307
    and "0 < b" and "b \<le> (q - 1) div 2"
wenzelm@41541
   308
  shows "(p * b < q * a) = (b \<le> q * a div p)"
nipkow@15392
   309
proof -
nipkow@15392
   310
  have "p * b < q * a ==> b \<le> q * a div p"
nipkow@15392
   311
  proof -
nipkow@15392
   312
    assume "p * b < q * a"
paulson@13871
   313
    then have "p * b \<le> q * a" by auto
nipkow@15392
   314
    then have "(p * b) div p \<le> (q * a) div p"
wenzelm@18369
   315
      by (rule zdiv_mono1) (insert p_g_2, auto)
nipkow@15392
   316
    then show "b \<le> (q * a) div p"
paulson@13871
   317
      apply (subgoal_tac "p \<noteq> 0")
nipkow@30034
   318
      apply (frule div_mult_self1_is_id, force)
wenzelm@18369
   319
      apply (insert p_g_2, auto)
wenzelm@18369
   320
      done
nipkow@15392
   321
  qed
nipkow@15392
   322
  moreover have "b \<le> q * a div p ==> p * b < q * a"
nipkow@15392
   323
  proof -
nipkow@15392
   324
    assume "b \<le> q * a div p"
nipkow@15392
   325
    then have "p * b \<le> p * ((q * a) div p)"
wenzelm@18369
   326
      using p_g_2 by (auto simp add: mult_le_cancel_left)
nipkow@15392
   327
    also have "... \<le> q * a"
wenzelm@18369
   328
      by (rule zdiv_leq_prop) (insert p_g_2, auto)
nipkow@15392
   329
    finally have "p * b \<le> q * a" .
nipkow@15392
   330
    then have "p * b < q * a | p * b = q * a"
paulson@13871
   331
      by (simp only: order_le_imp_less_or_eq)
nipkow@15392
   332
    moreover have "p * b \<noteq> q * a"
wenzelm@41541
   333
      by (rule pb_neq_qa) (insert assms, auto)
paulson@13871
   334
    ultimately show ?thesis by auto
nipkow@15392
   335
  qed
nipkow@15392
   336
  ultimately show ?thesis ..
nipkow@15392
   337
qed
paulson@13871
   338
wenzelm@41541
   339
lemma aux1b:
wenzelm@41541
   340
  assumes "0 < a" and "a \<le> (p - 1) div 2"
wenzelm@41541
   341
    and "0 < b" and "b \<le> (q - 1) div 2"
wenzelm@41541
   342
  shows "(q * a < p * b) = (a \<le> p * b div q)"
nipkow@15392
   343
proof -
nipkow@15392
   344
  have "q * a < p * b ==> a \<le> p * b div q"
nipkow@15392
   345
  proof -
nipkow@15392
   346
    assume "q * a < p * b"
paulson@13871
   347
    then have "q * a \<le> p * b" by auto
nipkow@15392
   348
    then have "(q * a) div q \<le> (p * b) div q"
wenzelm@18369
   349
      by (rule zdiv_mono1) (insert q_g_2, auto)
nipkow@15392
   350
    then show "a \<le> (p * b) div q"
paulson@13871
   351
      apply (subgoal_tac "q \<noteq> 0")
nipkow@30034
   352
      apply (frule div_mult_self1_is_id, force)
wenzelm@18369
   353
      apply (insert q_g_2, auto)
wenzelm@18369
   354
      done
nipkow@15392
   355
  qed
nipkow@15392
   356
  moreover have "a \<le> p * b div q ==> q * a < p * b"
nipkow@15392
   357
  proof -
nipkow@15392
   358
    assume "a \<le> p * b div q"
nipkow@15392
   359
    then have "q * a \<le> q * ((p * b) div q)"
wenzelm@18369
   360
      using q_g_2 by (auto simp add: mult_le_cancel_left)
nipkow@15392
   361
    also have "... \<le> p * b"
wenzelm@18369
   362
      by (rule zdiv_leq_prop) (insert q_g_2, auto)
nipkow@15392
   363
    finally have "q * a \<le> p * b" .
nipkow@15392
   364
    then have "q * a < p * b | q * a = p * b"
paulson@13871
   365
      by (simp only: order_le_imp_less_or_eq)
nipkow@15392
   366
    moreover have "p * b \<noteq> q * a"
wenzelm@41541
   367
      by (rule  pb_neq_qa) (insert assms, auto)
paulson@13871
   368
    ultimately show ?thesis by auto
nipkow@15392
   369
  qed
nipkow@15392
   370
  ultimately show ?thesis ..
nipkow@15392
   371
qed
paulson@13871
   372
wenzelm@41541
   373
lemma (in -) aux2:
wenzelm@41541
   374
  assumes "zprime p" and "zprime q" and "2 < p" and "2 < q"
wenzelm@41541
   375
  shows "(q * ((p - 1) div 2)) div p \<le> (q - 1) div 2"
nipkow@15392
   376
proof-
paulson@13871
   377
  (* Set up what's even and odd *)
wenzelm@41541
   378
  from assms have "p \<in> zOdd & q \<in> zOdd"
paulson@13871
   379
    by (auto simp add:  zprime_zOdd_eq_grt_2)
nipkow@15392
   380
  then have even1: "(p - 1):zEven & (q - 1):zEven"
paulson@13871
   381
    by (auto simp add: odd_minus_one_even)
nipkow@15392
   382
  then have even2: "(2 * p):zEven & ((q - 1) * p):zEven"
paulson@13871
   383
    by (auto simp add: zEven_def)
nipkow@15392
   384
  then have even3: "(((q - 1) * p) + (2 * p)):zEven"
paulson@14434
   385
    by (auto simp: EvenOdd.even_plus_even)
paulson@13871
   386
  (* using these prove it *)
wenzelm@41541
   387
  from assms have "q * (p - 1) < ((q - 1) * p) + (2 * p)"
paulson@13871
   388
    by (auto simp add: int_distrib)
nipkow@15392
   389
  then have "((p - 1) * q) div 2 < (((q - 1) * p) + (2 * p)) div 2"
nipkow@15392
   390
    apply (rule_tac x = "((p - 1) * q)" in even_div_2_l)
haftmann@57514
   391
    by (auto simp add: even3, auto simp add: ac_simps)
nipkow@15392
   392
  also have "((p - 1) * q) div 2 = q * ((p - 1) div 2)"
paulson@13871
   393
    by (auto simp add: even1 even_prod_div_2)
nipkow@15392
   394
  also have "(((q - 1) * p) + (2 * p)) div 2 = (((q - 1) div 2) * p) + p"
paulson@13871
   395
    by (auto simp add: even1 even2 even_prod_div_2 even_sum_div_2)
wenzelm@18369
   396
  finally show ?thesis
wenzelm@18369
   397
    apply (rule_tac x = " q * ((p - 1) div 2)" and
nipkow@15392
   398
                    y = "(q - 1) div 2" in div_prop2)
wenzelm@41541
   399
    using assms by auto
nipkow@15392
   400
qed
paulson@13871
   401
wenzelm@21233
   402
lemma aux3a: "\<forall>j \<in> P_set. int (card (f1 j)) = (q * j) div p"
nipkow@15392
   403
proof
nipkow@15392
   404
  fix j
nipkow@15392
   405
  assume j_fact: "j \<in> P_set"
nipkow@15392
   406
  have "int (card (f1 j)) = int (card {y. y \<in> Q_set & y \<le> (q * j) div p})"
nipkow@15392
   407
  proof -
nipkow@15392
   408
    have "finite (f1 j)"
nipkow@15392
   409
    proof -
paulson@13871
   410
      have "(f1 j) \<subseteq> S" by (auto simp add: f1_def)
paulson@13871
   411
      with S_finite show ?thesis by (auto simp add: finite_subset)
nipkow@15392
   412
    qed
nipkow@15392
   413
    moreover have "inj_on (%(x,y). y) (f1 j)"
paulson@13871
   414
      by (auto simp add: f1_def inj_on_def)
nipkow@15392
   415
    ultimately have "card ((%(x,y). y) ` (f1 j)) = card  (f1 j)"
paulson@13871
   416
      by (auto simp add: f1_def card_image)
nipkow@15392
   417
    moreover have "((%(x,y). y) ` (f1 j)) = {y. y \<in> Q_set & y \<le> (q * j) div p}"
wenzelm@41541
   418
      using j_fact by (auto simp add: f1_def S_def Q_set_def P_set_def image_def)
paulson@13871
   419
    ultimately show ?thesis by (auto simp add: f1_def)
nipkow@15392
   420
  qed
nipkow@15392
   421
  also have "... = int (card {y. 0 < y & y \<le> (q * j) div p})"
nipkow@15392
   422
  proof -
wenzelm@18369
   423
    have "{y. y \<in> Q_set & y \<le> (q * j) div p} =
nipkow@15392
   424
        {y. 0 < y & y \<le> (q * j) div p}"
paulson@13871
   425
      apply (auto simp add: Q_set_def)
wenzelm@18369
   426
    proof -
wenzelm@18369
   427
      fix x
wenzelm@41541
   428
      assume x: "0 < x" "x \<le> q * j div p"
wenzelm@18369
   429
      with j_fact P_set_def  have "j \<le> (p - 1) div 2" by auto
wenzelm@18369
   430
      with q_g_2 have "q * j \<le> q * ((p - 1) div 2)"
wenzelm@18369
   431
        by (auto simp add: mult_le_cancel_left)
wenzelm@18369
   432
      with p_g_2 have "q * j div p \<le> q * ((p - 1) div 2) div p"
wenzelm@18369
   433
        by (auto simp add: zdiv_mono1)
wenzelm@41541
   434
      also from QRTEMP_axioms j_fact P_set_def have "... \<le> (q - 1) div 2"
wenzelm@18369
   435
        apply simp
wenzelm@18369
   436
        apply (insert aux2)
wenzelm@18369
   437
        apply (simp add: QRTEMP_def)
wenzelm@18369
   438
        done
wenzelm@41541
   439
      finally show "x \<le> (q - 1) div 2" using x by auto
wenzelm@18369
   440
    qed
paulson@13871
   441
    then show ?thesis by auto
nipkow@15392
   442
  qed
nipkow@15392
   443
  also have "... = (q * j) div p"
nipkow@15392
   444
  proof -
paulson@13871
   445
    from j_fact P_set_def have "0 \<le> j" by auto
paulson@14387
   446
    with q_g_2 have "q * 0 \<le> q * j" by (auto simp only: mult_left_mono)
paulson@13871
   447
    then have "0 \<le> q * j" by auto
nipkow@15392
   448
    then have "0 div p \<le> (q * j) div p"
paulson@13871
   449
      apply (rule_tac a = 0 in zdiv_mono1)
wenzelm@18369
   450
      apply (insert p_g_2, auto)
wenzelm@18369
   451
      done
paulson@13871
   452
    also have "0 div p = 0" by auto
paulson@13871
   453
    finally show ?thesis by (auto simp add: card_bdd_int_set_l_le)
nipkow@15392
   454
  qed
nipkow@15392
   455
  finally show "int (card (f1 j)) = q * j div p" .
nipkow@15392
   456
qed
paulson@13871
   457
wenzelm@21233
   458
lemma aux3b: "\<forall>j \<in> Q_set. int (card (f2 j)) = (p * j) div q"
nipkow@15392
   459
proof
nipkow@15392
   460
  fix j
nipkow@15392
   461
  assume j_fact: "j \<in> Q_set"
nipkow@15392
   462
  have "int (card (f2 j)) = int (card {y. y \<in> P_set & y \<le> (p * j) div q})"
nipkow@15392
   463
  proof -
nipkow@15392
   464
    have "finite (f2 j)"
nipkow@15392
   465
    proof -
paulson@13871
   466
      have "(f2 j) \<subseteq> S" by (auto simp add: f2_def)
paulson@13871
   467
      with S_finite show ?thesis by (auto simp add: finite_subset)
nipkow@15392
   468
    qed
nipkow@15392
   469
    moreover have "inj_on (%(x,y). x) (f2 j)"
paulson@13871
   470
      by (auto simp add: f2_def inj_on_def)
nipkow@15392
   471
    ultimately have "card ((%(x,y). x) ` (f2 j)) = card  (f2 j)"
paulson@13871
   472
      by (auto simp add: f2_def card_image)
nipkow@15392
   473
    moreover have "((%(x,y). x) ` (f2 j)) = {y. y \<in> P_set & y \<le> (p * j) div q}"
wenzelm@41541
   474
      using j_fact by (auto simp add: f2_def S_def Q_set_def P_set_def image_def)
paulson@13871
   475
    ultimately show ?thesis by (auto simp add: f2_def)
nipkow@15392
   476
  qed
nipkow@15392
   477
  also have "... = int (card {y. 0 < y & y \<le> (p * j) div q})"
nipkow@15392
   478
  proof -
wenzelm@18369
   479
    have "{y. y \<in> P_set & y \<le> (p * j) div q} =
nipkow@15392
   480
        {y. 0 < y & y \<le> (p * j) div q}"
paulson@13871
   481
      apply (auto simp add: P_set_def)
wenzelm@18369
   482
    proof -
wenzelm@18369
   483
      fix x
wenzelm@41541
   484
      assume x: "0 < x" "x \<le> p * j div q"
wenzelm@18369
   485
      with j_fact Q_set_def  have "j \<le> (q - 1) div 2" by auto
wenzelm@18369
   486
      with p_g_2 have "p * j \<le> p * ((q - 1) div 2)"
wenzelm@18369
   487
        by (auto simp add: mult_le_cancel_left)
wenzelm@18369
   488
      with q_g_2 have "p * j div q \<le> p * ((q - 1) div 2) div q"
wenzelm@18369
   489
        by (auto simp add: zdiv_mono1)
wenzelm@41541
   490
      also from QRTEMP_axioms j_fact have "... \<le> (p - 1) div 2"
wenzelm@18369
   491
        by (auto simp add: aux2 QRTEMP_def)
wenzelm@41541
   492
      finally show "x \<le> (p - 1) div 2" using x by auto
nipkow@15392
   493
      qed
paulson@13871
   494
    then show ?thesis by auto
nipkow@15392
   495
  qed
nipkow@15392
   496
  also have "... = (p * j) div q"
nipkow@15392
   497
  proof -
paulson@13871
   498
    from j_fact Q_set_def have "0 \<le> j" by auto
paulson@14387
   499
    with p_g_2 have "p * 0 \<le> p * j" by (auto simp only: mult_left_mono)
paulson@13871
   500
    then have "0 \<le> p * j" by auto
nipkow@15392
   501
    then have "0 div q \<le> (p * j) div q"
paulson@13871
   502
      apply (rule_tac a = 0 in zdiv_mono1)
wenzelm@18369
   503
      apply (insert q_g_2, auto)
wenzelm@18369
   504
      done
paulson@13871
   505
    also have "0 div q = 0" by auto
paulson@13871
   506
    finally show ?thesis by (auto simp add: card_bdd_int_set_l_le)
nipkow@15392
   507
  qed
nipkow@15392
   508
  finally show "int (card (f2 j)) = p * j div q" .
nipkow@15392
   509
qed
paulson@13871
   510
wenzelm@21233
   511
lemma S1_card: "int (card(S1)) = setsum (%j. (q * j) div p) P_set"
nipkow@15392
   512
proof -
nipkow@15392
   513
  have "\<forall>x \<in> P_set. finite (f1 x)"
nipkow@15392
   514
  proof
nipkow@15392
   515
    fix x
paulson@13871
   516
    have "f1 x \<subseteq> S" by (auto simp add: f1_def)
paulson@13871
   517
    with S_finite show "finite (f1 x)" by (auto simp add: finite_subset)
nipkow@15392
   518
  qed
nipkow@15392
   519
  moreover have "(\<forall>x \<in> P_set. \<forall>y \<in> P_set. x \<noteq> y --> (f1 x) \<inter> (f1 y) = {})"
paulson@13871
   520
    by (auto simp add: f1_def)
nipkow@15392
   521
  moreover note P_set_finite
wenzelm@18369
   522
  ultimately have "int(card (UNION P_set f1)) =
nipkow@15392
   523
      setsum (%x. int(card (f1 x))) P_set"
nipkow@15402
   524
    by(simp add:card_UN_disjoint int_setsum o_def)
nipkow@15392
   525
  moreover have "S1 = UNION P_set f1"
paulson@13871
   526
    by (auto simp add: f1_def S_def S1_def S2_def P_set_def Q_set_def aux1a)
wenzelm@18369
   527
  ultimately have "int(card (S1)) = setsum (%j. int(card (f1 j))) P_set"
paulson@13871
   528
    by auto
nipkow@15392
   529
  also have "... = setsum (%j. q * j div p) P_set"
haftmann@57418
   530
    using aux3a by(fastforce intro: setsum.cong)
nipkow@15392
   531
  finally show ?thesis .
nipkow@15392
   532
qed
paulson@13871
   533
wenzelm@21233
   534
lemma S2_card: "int (card(S2)) = setsum (%j. (p * j) div q) Q_set"
nipkow@15392
   535
proof -
nipkow@15392
   536
  have "\<forall>x \<in> Q_set. finite (f2 x)"
nipkow@15392
   537
  proof
nipkow@15392
   538
    fix x
paulson@13871
   539
    have "f2 x \<subseteq> S" by (auto simp add: f2_def)
paulson@13871
   540
    with S_finite show "finite (f2 x)" by (auto simp add: finite_subset)
nipkow@15392
   541
  qed
wenzelm@18369
   542
  moreover have "(\<forall>x \<in> Q_set. \<forall>y \<in> Q_set. x \<noteq> y -->
nipkow@15392
   543
      (f2 x) \<inter> (f2 y) = {})"
paulson@13871
   544
    by (auto simp add: f2_def)
nipkow@15392
   545
  moreover note Q_set_finite
wenzelm@18369
   546
  ultimately have "int(card (UNION Q_set f2)) =
nipkow@15392
   547
      setsum (%x. int(card (f2 x))) Q_set"
nipkow@15402
   548
    by(simp add:card_UN_disjoint int_setsum o_def)
nipkow@15392
   549
  moreover have "S2 = UNION Q_set f2"
paulson@13871
   550
    by (auto simp add: f2_def S_def S1_def S2_def P_set_def Q_set_def aux1b)
wenzelm@18369
   551
  ultimately have "int(card (S2)) = setsum (%j. int(card (f2 j))) Q_set"
paulson@13871
   552
    by auto
nipkow@15392
   553
  also have "... = setsum (%j. p * j div q) Q_set"
haftmann@57418
   554
    using aux3b by(fastforce intro: setsum.cong)
nipkow@15392
   555
  finally show ?thesis .
nipkow@15392
   556
qed
paulson@13871
   557
wenzelm@21233
   558
lemma S1_carda: "int (card(S1)) =
nipkow@15392
   559
    setsum (%j. (j * q) div p) P_set"
haftmann@57514
   560
  by (auto simp add: S1_card ac_simps)
paulson@13871
   561
wenzelm@21233
   562
lemma S2_carda: "int (card(S2)) =
nipkow@15392
   563
    setsum (%j. (j * p) div q) Q_set"
haftmann@57514
   564
  by (auto simp add: S2_card ac_simps)
paulson@13871
   565
wenzelm@21233
   566
lemma pq_sum_prop: "(setsum (%j. (j * p) div q) Q_set) +
nipkow@15392
   567
    (setsum (%j. (j * q) div p) P_set) = ((p - 1) div 2) * ((q - 1) div 2)"
nipkow@15392
   568
proof -
wenzelm@18369
   569
  have "(setsum (%j. (j * p) div q) Q_set) +
nipkow@15392
   570
      (setsum (%j. (j * q) div p) P_set) = int (card S2) + int (card S1)"
paulson@13871
   571
    by (auto simp add: S1_carda S2_carda)
nipkow@15392
   572
  also have "... = int (card S1) + int (card S2)"
paulson@13871
   573
    by auto
nipkow@15392
   574
  also have "... = ((p - 1) div 2) * ((q - 1) div 2)"
paulson@13871
   575
    by (auto simp add: card_sum_S1_S2)
nipkow@15392
   576
  finally show ?thesis .
nipkow@15392
   577
qed
paulson@13871
   578
wenzelm@21233
   579
wenzelm@21288
   580
lemma (in -) pq_prime_neq: "[| zprime p; zprime q; p \<noteq> q |] ==> (~[p = 0] (mod q))"
paulson@13871
   581
  apply (auto simp add: zcong_eq_zdvd_prop zprime_def)
paulson@13871
   582
  apply (drule_tac x = q in allE)
paulson@13871
   583
  apply (drule_tac x = p in allE)
wenzelm@18369
   584
  apply auto
wenzelm@18369
   585
  done
paulson@13871
   586
wenzelm@21233
   587
wenzelm@21233
   588
lemma QR_short: "(Legendre p q) * (Legendre q p) =
nipkow@15392
   589
    (-1::int)^nat(((p - 1) div 2)*((q - 1) div 2))"
nipkow@15392
   590
proof -
wenzelm@41541
   591
  from QRTEMP_axioms have "~([p = 0] (mod q))"
paulson@13871
   592
    by (auto simp add: pq_prime_neq QRTEMP_def)
wenzelm@41541
   593
  with QRTEMP_axioms Q_set_def have a1: "(Legendre p q) = (-1::int) ^
nipkow@15392
   594
      nat(setsum (%x. ((x * p) div q)) Q_set)"
paulson@13871
   595
    apply (rule_tac p = q in  MainQRLemma)
wenzelm@18369
   596
    apply (auto simp add: zprime_zOdd_eq_grt_2 QRTEMP_def)
wenzelm@18369
   597
    done
wenzelm@41541
   598
  from QRTEMP_axioms have "~([q = 0] (mod p))"
paulson@13871
   599
    apply (rule_tac p = q and q = p in pq_prime_neq)
nipkow@15392
   600
    apply (simp add: QRTEMP_def)+
nipkow@16733
   601
    done
wenzelm@41541
   602
  with QRTEMP_axioms P_set_def have a2: "(Legendre q p) =
nipkow@15392
   603
      (-1::int) ^ nat(setsum (%x. ((x * q) div p)) P_set)"
paulson@13871
   604
    apply (rule_tac p = p in  MainQRLemma)
wenzelm@18369
   605
    apply (auto simp add: zprime_zOdd_eq_grt_2 QRTEMP_def)
wenzelm@18369
   606
    done
wenzelm@18369
   607
  from a1 a2 have "(Legendre p q) * (Legendre q p) =
paulson@13871
   608
      (-1::int) ^ nat(setsum (%x. ((x * p) div q)) Q_set) *
nipkow@15392
   609
        (-1::int) ^ nat(setsum (%x. ((x * q) div p)) P_set)"
paulson@13871
   610
    by auto
wenzelm@18369
   611
  also have "... = (-1::int) ^ (nat(setsum (%x. ((x * p) div q)) Q_set) +
nipkow@15392
   612
                   nat(setsum (%x. ((x * q) div p)) P_set))"
huffman@44766
   613
    by (auto simp add: power_add)
wenzelm@18369
   614
  also have "nat(setsum (%x. ((x * p) div q)) Q_set) +
paulson@13871
   615
      nat(setsum (%x. ((x * q) div p)) P_set) =
wenzelm@18369
   616
        nat((setsum (%x. ((x * p) div q)) Q_set) +
nipkow@15392
   617
          (setsum (%x. ((x * q) div p)) P_set))"
wenzelm@20898
   618
    apply (rule_tac z = "setsum (%x. ((x * p) div q)) Q_set" in
wenzelm@18369
   619
      nat_add_distrib [symmetric])
wenzelm@18369
   620
    apply (auto simp add: S1_carda [symmetric] S2_carda [symmetric])
wenzelm@18369
   621
    done
nipkow@15392
   622
  also have "... = nat(((p - 1) div 2) * ((q - 1) div 2))"
paulson@13871
   623
    by (auto simp add: pq_sum_prop)
nipkow@15392
   624
  finally show ?thesis .
nipkow@15392
   625
qed
paulson@13871
   626
wenzelm@21233
   627
end
wenzelm@21233
   628
paulson@13871
   629
theorem Quadratic_Reciprocity:
wenzelm@18369
   630
     "[| p \<in> zOdd; zprime p; q \<in> zOdd; zprime q;
wenzelm@18369
   631
         p \<noteq> q |]
wenzelm@18369
   632
      ==> (Legendre p q) * (Legendre q p) =
nipkow@15392
   633
          (-1::int)^nat(((p - 1) div 2)*((q - 1) div 2))"
wenzelm@18369
   634
  by (auto simp add: QRTEMP.QR_short zprime_zOdd_eq_grt_2 [symmetric]
paulson@13871
   635
                     QRTEMP_def)
paulson@13871
   636
paulson@13871
   637
end