Theory Voronoi_Congruence
section ‹The Voronoi congruence›
theory Voronoi_Congruence
imports Kummer_Library Rat_Congruence "HOL-Algebra.Residues_Algebra"
begin
unbundle bernoulli_syntax
lemma sum_of_powers_mod_prime:
assumes p: "prime p"
shows "[(∑x=1..<p. int x ^ m) = (if (p - 1) dvd m then -1 else 0)] (mod p)"
proof -
obtain g where g: "residue_primroot p g"
using assms prime_gt_1_nat prime_primitive_root_exists by auto
have "coprime g p"
using g by (auto simp: residue_primroot_def coprime_commute)
have bij: "bij_betw (λi. g ^ i mod p) {..<p-1} {0<..<p}"
using residue_primroot_is_generator[OF _ g] p
by (simp add: totient_prime totatives_prime prime_gt_Suc_0_nat)
have "(∑x=1..<p. int x ^ m) = (∑x∈{0<..<p}. int x ^ m)"
by (intro sum.cong) auto
also have "… = (∑i<p-1. int (g ^ i mod p) ^ m)"
by (subst sum.reindex_bij_betw[OF bij, symmetric]) auto
also have "[… = (∑i<p-1. int (g ^ i) ^ m)] (mod p)"
by (intro cong_sum cong_pow cong_int) auto
also have "(∑i<p-1. int (g ^ i) ^ m) = (∑i<p-1. int (g ^ m) ^ i)"
by (simp flip: power_mult add: mult.commute)
also have "[… = (∑i<p-1. int (g ^ m mod p) ^ i)] (mod p)"
by (intro cong_sum cong_pow cong_int) auto
also have "[(∑i<p-1. int (g ^ m mod p) ^ i) = (if (p - 1) dvd m then -1 else 0)] (mod p)"
proof (cases "(p - 1) dvd m")
case True
have "[(∑i<p-1. int (g ^ m mod p) ^ i) = (∑i<p-1. int (g ^ 0) ^ i)] (mod p)"
using ‹coprime g p› p True
by (intro cong_sum cong_pow cong_pow_totient cong_mod_left cong_refl cong_int)
(auto simp: cong_0_iff totient_prime)
also have "(∑i<p-1. int (g ^ 0) ^ i) = int p - 1"
using prime_gt_1_nat[OF p] by (simp add: of_nat_diff)
also have "[int p - 1 = 0 - 1] (mod int p)"
by (intro cong_diff) (auto simp: Cong.cong_def)
finally show ?thesis
using True by auto
next
case False
have not_cong: "[g ^ m ≠ 1] (mod p)"
using False g by (metis assms ord_divides residue_primroot_def totient_prime)
hence neq1: "g ^ m mod p ≠ 1"
using prime_gt_1_nat[OF p] by (auto simp: Cong.cong_def)
have "real_of_int (int (∑i<p-1. (g ^ m mod p) ^ i)) = (∑i<p-1. real (g ^ m mod p) ^ i)"
by simp
also have "… = (1 - real (g ^ m mod p) ^ (p - 1)) / (1 - real (g ^ m mod p))"
using prime_gt_1_nat[OF p] neq1 by (subst sum_gp_strict) (auto simp: of_nat_diff)
finally have "real_of_int (int (∑i<p-1. (g ^ m mod p) ^ i)) * (1 - real (g ^ m mod p)) =
1 - real (g ^ m mod p) ^ (p - 1)"
using neq1 by (simp add: field_simps)
also have "real_of_int (int (∑i<p-1. (g ^ m mod p) ^ i)) * (1 - real (g ^ m mod p)) =
real_of_int ((∑i<p-1. int (g ^ m mod p) ^ i) * (1 - int (g ^ m mod p)))"
by simp
also have "1 - real (g ^ m mod p) ^ (p - 1) = real_of_int (1 - int (g ^ m mod p) ^ (p - 1))"
by simp
finally have "(∑i<p-1. int (g ^ m mod p) ^ i) * (1 - int (g ^ m mod p)) = 1 - int (g ^ m mod p) ^ (p - 1)"
by linarith
also have "[1 - int (g ^ m mod p) ^ (p - 1) = 1 - int (g ^ m) ^ (p - 1)] (mod p)"
by (intro cong_diff cong_int cong_pow) auto
also have "int (g ^ m) ^ (p - 1) = int ((g ^ (p - 1)) ^ m)"
by (simp flip: power_mult add: mult.commute)
also have "[1 - int ((g ^ (p - 1)) ^ m) = 1 - int ((g ^ 0) ^ m)] (mod p)"
using ‹coprime g p› p
by (intro cong_diff cong_int cong_pow_totient cong_refl)
(auto simp: Cong.cong_def totient_prime)
finally have "[(∑i<p-1. int (g ^ m mod p) ^ i) * (1 - int (g ^ m mod p)) = 0] (mod p)"
by simp
hence "p dvd (∑i<p-1. int (g ^ m mod p) ^ i) * (1 - int (g ^ m mod p))"
by (simp add: cong_0_iff)
moreover from not_cong have "¬p dvd (1 - int (g ^ m mod p))"
by (metis of_nat_1 cong_iff_dvd_diff mod_mod_trivial nat_int of_nat_mod Cong.cong_def)
ultimately have "p dvd (∑i<p-1. int (g ^ m mod p) ^ i)"
using p by (subst (asm) prime_dvd_mult_iff) auto
thus ?thesis
using False by (simp add: Cong.cong_def)
qed
finally show ?thesis .
qed
lemma sum_of_powers_mod_prime':
fixes p m :: nat
assumes p: "prime p" "¬(p - 1) dvd m"
shows "[(∑x=1..<p. x ^ m) = 0] (mod p)"
proof -
have "[(∑x=1..<p. int x ^ m) = int 0] (mod p)"
using sum_of_powers_mod_prime[of p m] assms by simp
also have "(∑x=1..<p. int x ^ m) = int (∑x=1..<p. x ^ m)"
by simp
finally show ?thesis
using cong_int_iff by blast
qed
lemma voronoi_congruence_aux1:
assumes "prime p" "j ≥ 4"
shows "multiplicity p (j + 1) ≤ (if p ∈ {2, 3} then 1 else 0) + j - 2"
proof (cases "p ∈ {2, 3}")
case True
have "multiplicity p (j + 1) < j"
proof (rule multiplicity_lessI)
have "2 ^ (n + 2) > n + 3" for n
by (induction n) auto
from this[of "j - 2"] have "j + 1 < 2 ^ j"
using assms(2) by (simp del: power_Suc add: Suc_diff_Suc eval_nat_numeral)
also have "2 ^ j ≤ p ^ j"
using True by (intro power_mono) auto
finally have "p ^ j > j + 1" .
thus "¬p ^ j dvd j + 1"
using dvd_imp_le by force
qed (use assms in auto)
with True show ?thesis
by simp
next
case False
have "p ≠ 0" "p ≠ 1" "p ≠ 4"
using assms by auto
with False have "p ≥ 5"
by force
have "multiplicity p (j + 1) < j - 1"
proof (rule multiplicity_lessI)
have "5 ^ (n + 1) > n + 3" for n
by (induction n) auto
from this[of "j - 2"] have "j + 1 < 5 ^ (j - 1)"
using assms(2) by (simp del: power_Suc add: Suc_diff_Suc eval_nat_numeral)
also have "5 ^ (j - 1) ≤ p ^ (j - 1)"
using ‹p ≥ 5› by (intro power_mono) auto
finally have "p ^ (j - 1) > j + 1" .
thus "¬p ^ (j - 1) dvd j + 1"
using dvd_imp_le by force
qed (use assms in auto)
with False show ?thesis
by simp
qed
context
fixes S :: "nat ⇒ nat ⇒ nat" and D :: "nat ⇒ nat" and N :: "nat ⇒ int"
defines "S ≡ (λk n. ∑r<n. r ^ k)"
defines "N ≡ bernoulli_num" and "D ≡ bernoulli_denom"
begin
lemma voronoi_congruence_aux2:
fixes k n :: nat
assumes k: "even k" "k ≥ 2" and n: "n > 0"
shows "real (S k n) = (∑j≤k. real (k choose j) / real (j + 1) * bernoulli (k - j) * real (n ^ (j + 1)))"
proof -
have "real (S k n) = (∑r≤n-1. real r ^ k)"
using n unfolding S_def of_nat_sum by (intro sum.cong) auto
also have "… = (bernpoly (Suc k) (real n) - bernoulli (Suc k)) / (real k + 1)"
using n by (subst sum_of_powers) (auto simp: of_nat_diff)
also have "bernoulli (Suc k) = 0"
using k by (intro bernoulli_odd_eq_0) auto
also have "(bernpoly (Suc k) (real n) - 0) / (real k + 1) =
bernpoly (Suc k) (real n) / real (k + 1)"
by simp
also have "bernpoly (Suc k) (real n) / real (k + 1) = (∑j≤Suc k. (Suc k choose j) / (k + 1) * bernoulli (Suc k - j) * n ^ j)"
by (subst bernpoly_altdef)
(auto simp: sum_divide_distrib sum_distrib_left sum_distrib_right field_simps simp del: of_nat_Suc)
also have "… = (∑j=1..Suc k. (Suc k choose j) / (k+1) * bernoulli (Suc k - j) * n ^ j)"
using k by (intro sum.mono_neutral_right) (auto simp: not_le simp: bernoulli_odd_eq_0)
also have "… = (∑j≤k. (Suc k choose Suc j) / (k+1) * bernoulli (k - j) * n ^ (j + 1))"
by (intro sum.reindex_bij_witness[of _ "λj. j+1" "λj. j-1"]) (auto simp: of_nat_diff)
also have "… = (∑j≤k. (k choose j) / (j+1) * bernoulli (k - j) * n ^ (j + 1))"
proof (intro sum.cong refl, goal_cases)
case (1 j)
have "real (Suc j * (Suc k choose Suc j)) = real (Suc k * (k choose j))"
by (subst Suc_times_binomial_eq) (simp add: mult_ac)
thus ?case
unfolding of_nat_mult by (simp add: field_simps del: of_nat_Suc binomial_Suc_Suc)
qed
finally show ?thesis .
qed
lemma voronoi_congruence_aux3:
fixes k n :: nat
assumes k: "even k" "k ≥ 2" and n: "n > 0"
shows "[D k * S k n = N k * n] (mod (n^2))"
proof -
note [simp del] = div_mult_self3 div_mult_self4 div_mult_self2 div_mult_self1
define A :: "nat ⇒ rat"
where "A = (λj. of_nat (k choose j) * of_int (N (k - j)) / of_nat (D (k - j)) * of_nat n powi (int j - 1) / of_nat (Suc j))"
have "real (S k n) = (∑j≤k. real (k choose j) / real (j + 1) * bernoulli (k - j) * real (n ^ (j + 1)))"
by (rule voronoi_congruence_aux2) fact+
also have "… = (∑j≤k. of_rat (A j) * n⇧2)"
unfolding A_def using n
by (intro sum.cong)
(auto simp: power_int_diff power2_eq_square N_def D_def bernoulli_conv_num_denom
of_rat_mult of_rat_divide field_simps of_rat_power simp del: of_nat_Suc)
also have "… = (∑j≤k. of_rat (A j)) * real (n ^ 2)"
by (simp add: sum_distrib_right)
also have "(∑j≤k. of_rat (A j)) = (∑j∈insert 0 {1..k}. of_rat (A j))"
using k by (intro sum.cong) auto
also have "… = of_rat (A 0) + (∑j=1..k. of_rat (A j))"
by (subst sum.insert) auto
also have "of_rat (A 0) = bernoulli k / n"
using n by (auto simp: A_def bernoulli_conv_num_denom N_def D_def field_simps
of_rat_mult of_rat_divide)
also have "(bernoulli k / n + (∑j=1..k. of_rat (A j))) * real (n ^ 2) =
real n * bernoulli k + (∑j=1..k. of_rat (A j)) * real (n ^ 2)"
using n by (simp add: field_simps power2_eq_square)
finally have eq1: "real (S k n) = real n * bernoulli k + (∑j=1..k. of_rat (A j)) * real (n ^ 2)" .
have "∃ab. coprime (fst ab) (snd ab) ∧ coprime (snd ab) (int n) ∧ snd ab > 0 ∧
6 * A j = of_int (fst ab) / of_int (snd ab)" (is "∃ab. ?P j ab") if j: "j ∈ {1..k}" for j
proof (cases "A j = 0")
case True
thus ?thesis
by (intro exI[of _ "(0, 1)"]) auto
next
case False
obtain a b :: int where ab: "coprime a b" "b > 0" "6 * A j = of_int a / of_int b"
by (metis Fract_of_int_quotient Rat_cases)
have *: "qmultiplicity p (6 * A j) ≥ 0" if p: "prime p" "p dvd n" for p
proof -
consider "j = 1" | "j = 2" | "j = k - 1" | "odd j" "j ≠ k - 1" | "j ≥ 3" "even j"
using j by force
thus ?thesis
proof cases
assume [simp]: "j = 1"
show ?thesis
proof (cases "k = 2")
case False
have "(of_rat (6 * A j) :: real) = 3 * real k * bernoulli (k - 1)"
by (simp add: A_def N_def D_def of_rat_mult of_rat_divide bernoulli_conv_num_denom)
also have "bernoulli (k - 1) = 0"
using k False by (subst bernoulli_odd_eq_0) auto
finally show ?thesis
by simp
next
case [simp]: True
have "qmultiplicity (int p) (6 * A j) = qmultiplicity (int p) 3"
by (simp add: A_def N_def D_def bernoulli_num_def floor_minus)
also have "… ≥ 0"
by auto
finally show ?thesis .
qed
next
assume [simp]: "j = 2"
have "6 * A j = rat_of_int (2 * n * (k choose 2) * N (k - 2)) / rat_of_int (D (k - 2))"
by (simp add: A_def)
also have "qmultiplicity (int p) … =
int (multiplicity (int p) (2 * int n * int (k choose 2) * N (k - 2))) -
int (multiplicity (int p) (D (k - 2)))" using k n p
by (subst qmultiplicity_divide_of_int) (auto simp: D_def N_def bernoulli_num_eq_0_iff)
also have "… ≥ int 1 - int 1"
proof (intro diff_mono; unfold of_nat_le_iff)
show "multiplicity (int p) (2 * int n * int (k choose 2) * N (k - 2)) ≥ 1"
using k n j p by (intro multiplicity_geI) (auto simp: N_def bernoulli_num_eq_0_iff)
next
show "multiplicity (int p) (D (k - 2)) ≤ 1" using p
by (intro squarefree_imp_multiplicity_prime_le_1)
(auto simp: D_def squarefree_bernoulli_denom)
qed
finally show ?thesis
by simp
next
assume [simp]: "j = k - 1"
have "6 * A j = -rat_of_nat (3 * n ^ (k - 2))"
using k binomial_symmetric[of 1 k, symmetric]
by (auto simp: A_def D_def N_def bernoulli_num_def floor_minus of_nat_diff
power_int_def nat_diff_distrib)
also have "qmultiplicity (int p) … ≥ 0"
unfolding qmultiplicity_minus by (subst qmultiplicity_of_nat) auto
finally show ?thesis .
next
assume "odd j" "j ≠ k - 1"
with k j have "odd (k - j)" "k - j ≠ 1"
by auto
hence "6 * A j = 0"
by (auto simp: A_def bernoulli_num_odd_eq_0 N_def)
thus ?thesis
by simp
next
assume "j ≥ 3" "even j"
with j have j: "j ∈ {3..k}"
by auto
have "6 * A j = rat_of_int (6 * int (k choose j) * N (k - j) * n ^ (j - 1)) /
rat_of_int (int (D (k - j)) * int (j + 1))"
using j by (simp add: A_def power_int_def nat_diff_distrib algebra_simps)
also have "qmultiplicity p … =
int (multiplicity (int p) (6 * int (k choose j) * N (k - j) * n ^ (j - 1))) -
int (multiplicity (int p) (int (D (k - j)) * int (j + 1)))" using k n p j ‹even j›
by (subst qmultiplicity_divide_of_int) (auto simp: D_def N_def bernoulli_num_eq_0_iff)
also have "… ≥ ((if p ∈ {2,3} then 1 else 0) + int j - 1) - ((if p ∈ {2,3} then 1 else 0) + int j - 1)"
proof (intro diff_mono, goal_cases)
case 1
have "multiplicity (int p) (6 * int (k choose j) * N (k - j) * int (n ^ (j - 1))) =
multiplicity (int p) (6 * (int (k choose j) * N (k - j) * int (n ^ (j - 1))))"
by (simp add: mult_ac)
also have "multiplicity (int p) (6 * (int (k choose j) * N (k - j) * int (n ^ (j - 1)))) =
multiplicity (int p) (2 * 3) + multiplicity (int p) (int (k choose j) * N (k - j) * int (n ^ (j - 1)))"
using k n p j ‹even j›
by (subst prime_elem_multiplicity_mult_distrib) (auto simp: N_def bernoulli_num_eq_0_iff)
also have "multiplicity (int p) (2 * 3) = (if p ∈ {2, 3} then 1 else 0)"
using p by (subst prime_elem_multiplicity_mult_distrib) (auto simp: multiplicity_prime_prime)
finally have "multiplicity (int p) (6 * int (k choose j) * N (k - j) * int (n ^ (j - 1))) =
(if p ∈ {2, 3} then 1 else 0) +
multiplicity (int p) (int (k choose j) * N (k - j) * int (n ^ (j - 1)))" .
moreover have "p ^ (j - 1) dvd n ^ (j - 1)"
using p by (intro dvd_power_same)
hence "multiplicity (int p) (int (k choose j) * N (k - j) * int (n ^ (j - 1))) ≥ j - 1"
using j k n ‹even j› p by (intro multiplicity_geI) (auto simp: N_def bernoulli_num_eq_0_iff)
hence "int (multiplicity (int p) (int (k choose j) * N (k - j) * int (n ^ (j - 1)))) ≥ int j - 1"
using ‹j ≥ 3› by linarith
ultimately show ?case
by simp
next
case 2
have "multiplicity (int p) (int (D (k - j)) * int (j + 1)) =
multiplicity (int p) (int (D (k - j))) + multiplicity (int p) (int (j + 1))"
using p by (subst prime_elem_multiplicity_mult_distrib) (auto simp: D_def)
moreover have "multiplicity (int p) (int (D (k - j))) ≤ 1" using p
by (intro squarefree_imp_multiplicity_prime_le_1)
(auto simp: D_def squarefree_bernoulli_denom)
moreover have "multiplicity (int p) (int (j + 1)) ≤ (if p ∈ {2, 3} then 1 else 0) + j - 2"
by (subst multiplicity_int, rule voronoi_congruence_aux1)
(use p j ‹even j› in auto)
hence "int (multiplicity (int p) (int (j + 1))) ≤ (if p ∈ {2, 3} then 1 else 0) + int j - 2"
using j by auto
ultimately show ?case
using ‹j ≥ 3› by linarith
qed
finally show ?thesis
by simp
qed
qed
have "coprime b n"
proof (subst coprime_commute, rule coprimeI_by_prime_factors)
fix p assume p: "p ∈ prime_factors (int n)"
hence "p > 0"
by (auto simp: in_prime_factors_iff prime_gt_0_int)
hence "qmultiplicity (nat p) (rat_of_int a / rat_of_int b) ≥ 0"
using *[of "nat p"] p unfolding ab by (auto simp: in_prime_factors_iff nat_dvd_iff)
thus "¬p dvd b"
using ab False ‹p > 0› p by (subst (asm) qmultiplicity_nonneg_iff) auto
qed (use n in auto)
with ab show ?thesis
by (intro exI[of _ "(a, b)"]) auto
qed
then obtain f where f: "⋀j. j ∈ {1..k} ⟹ ?P j (f j)"
by metis
define B :: int where "B = Lcm ((snd ∘ f) ` {1..k})"
have B: "coprime B n"
unfolding B_def using f by (auto intro!: coprime_Lcm_left)
define b' where "b' = (λj. B div snd (f j))"
define T where "T = (∑j=1..k. fst (f j) * b' j)"
have "real_of_int (B * int (D k * S k n)) =
real_of_int B * (real (D k) * bernoulli k) * real n +
real (D k) / 6 * (∑j=1..k. real_of_rat (6 * A j * of_int B)) * real n ^ 2"
unfolding of_int_mult of_nat_mult of_int_of_nat_eq
by (subst eq1) (simp_all add: algebra_simps of_rat_mult sum_distrib_left)
also have "real (D k) * bernoulli k = real_of_int (N k)"
by (simp add: bernoulli_conv_num_denom N_def D_def)
also have "(∑j=1..k. real_of_rat (6 * A j * of_int B)) = T"
unfolding T_def of_int_sum
proof (intro sum.cong refl, goal_cases)
case j: (1 j)
have "6 * A j = of_int (fst (f j)) / of_int (snd (f j))"
using f[OF j] by auto
also have "… * of_int B = of_int (fst (f j)) * (of_int B / of_int (snd (f j)))"
by simp
also have "of_int B / of_int (snd (f j)) = (of_int (B div snd (f j)) :: rat)"
by (subst of_int_div) (use j in ‹auto simp: B_def›)
finally show ?case
by (simp add: of_rat_mult b'_def)
qed
also have "real (D k) / 6 = real (D k div 6)"
by (subst real_of_nat_div) (use k in ‹auto intro!: six_divides_bernoulli_denom simp: D_def›)
also have "of_int B * of_int (N k) * real n + real (D k div 6) * of_int T * (real n)⇧2 =
of_int (B * N k * int n + int (D k div 6) * T * int n ^ 2)"
by (simp add: algebra_simps)
finally have "B * int (D k * S k n) = B * N k * int n + int (D k div 6) * T * int n ^ 2"
by linarith
hence "[B * int (D k * S k n) = B * N k * int n + int (D k div 6) * T * int n ^ 2] (mod (int n ^ 2))"
by simp
also have "[B * N k * int n + int (D k div 6) * T * int n ^ 2 =
B * N k * int n + int (D k div 6) * T * 0] (mod (int n ^ 2))"
by (intro cong_add cong_mult cong_refl) (auto simp: Cong.cong_def)
finally have "[B * int (D k * S k n) = B * (N k * int n)] (mod (int n)⇧2)"
by (simp add: mult_ac)
hence "[int (D k * S k n) = N k * int n] (mod (int n)⇧2)"
by (subst (asm) cong_mult_lcancel) (use B in auto)
thus ?thesis
by simp
qed
text ‹
Proposition 9.5.20
›
theorem voronoi_congruence:
fixes k n :: nat and a :: int
assumes k: "even k" "k ≥ 2" and n: "n > 0" and a: "coprime a n"
shows "[(a^k-1) * N k = k * a^(k-1) * D k * (∑m=1..<n. m^(k-1) * ((m * a) div n))] (mod n)"
proof -
define a' where "a' = modular_inverse (int n) a"
define q r where "q = (λm. (a * m) div n)" and "r = (λm. (a * m) mod n)"
have "S k n = (∑m=1..<n. m ^ k)"
using k unfolding S_def by (intro sum.mono_neutral_right) auto
hence "a ^ k * S k n = (∑m=1..<n. (a * m) ^ k)"
by (simp add: sum_distrib_left power_mult_distrib)
also have "[(∑m=1..<n. (a * m) ^ k) = (∑m=1..<n. r m ^ k + k * q m * n * (m * a) ^ (k - 1))] (mod n⇧2)"
proof (rule cong_sum)
fix m :: nat
have "[(∑j≤k. int (k choose j) * (q m * n) ^ j * r m ^ (k - j)) =
(∑j≤k. if j > 1 then 0 else (k choose j) * q m ^ j * r m ^ (k - j) * n ^ j)] (mod (n⇧2))"
proof (intro cong_sum, goal_cases)
case (1 j)
have dvd: "int n ^ 2 dvd int n ^ j" if "j > 1" for j
using that by (intro le_imp_power_dvd) auto
have eq: "int (k choose j) * (q m * n) ^ j * r m ^ (k - j) =
int (k choose j) * q m ^ j * r m ^ (k - j) * n ^ j"
using 1 by (simp add: algebra_simps flip: power_add)
have "[int (k choose j) * q m ^ j * r m ^ (k - j) * n ^ j =
(if j > 1 then 0 else int (k choose j) * q m ^ j * r m ^ (k - j) * n ^ j)] (mod (n⇧2))"
using dvd by (auto simp: cong_0_iff)
thus ?case
by (simp only: eq)
qed
also have "(∑j≤k. if j > 1 then 0 else (k choose j) * q m ^ j * r m ^ (k - j) * n ^ j) =
(∑j∈{0,1}. (k choose j) * q m ^ j * r m ^ (k - j) * n ^ j)"
using k by (intro sum.mono_neutral_cong_right) auto
also have "… = r m ^ k + (k * q m * n) * r m ^ (k-1)"
by simp
also have "[(k * q m * n) * (q m * 0 + r m) ^ (k-1) =
(k * q m * n) * (q m * n + r m) ^ (k-1)] (mod (int n)⇧2)"
by (intro cong_mult_square cong_pow cong_add cong_mult cong_refl) (auto simp: Cong.cong_def)
hence "[r m ^ k + (k * q m * n) * r m ^ (k-1) =
r m ^ k + (k * q m * n) * (q m * n + r m) ^ (k-1)] (mod n⇧2)"
by (intro cong_add) simp_all
also have "q m * n + r m = (m * a)"
by (simp add: q_def r_def)
also have "(∑j≤k. int (k choose j) * (q m * n) ^ j * r m ^ (k - j)) = (q m * n + r m) ^ k"
by (rule binomial_ring [symmetric])
also have "q m * n + r m = a * m"
by (simp add: q_def r_def)
finally show "[(a * m) ^ k = r m ^ k + k * q m * n * (m * a) ^ (k - 1)] (mod n⇧2)" .
qed
also have "(∑m=1..<n. r m ^ k + k * q m * n * (m * a) ^ (k - 1)) =
(∑m=1..<n. r m ^ k) + n * k * a^(k-1) * (∑m=1..<n. q m * m^(k-1))"
by (simp add: sum.distrib sum_distrib_left sum_distrib_right mult_ac power_mult_distrib)
also have "(∑m=1..<n. r m ^ k) = (∑m=1..<int n. r m ^ k)"
by (intro sum.reindex_bij_witness[of _ nat int]) auto
also have "… = (∑m=1..<int n. m ^ k)"
by (rule sum.reindex_bij_betw)
(use a bij_betw_int_remainders_mult[of a] in ‹simp_all add: r_def›)
also have "… = of_nat (∑m=1..<n. m ^ k)"
unfolding of_nat_sum by (intro sum.reindex_bij_witness[of _ int nat]) auto
also have "(∑m=1..<n. m ^ k) = S k n"
using k unfolding S_def by (intro sum.mono_neutral_left) auto
finally have "[a ^ k * S k n - S k n =
(S k n + n * k * a^(k-1) * (∑m=1..<n. q m * m^(k-1))) - S k n] (mod n⇧2)"
by (intro cong_diff cong_refl)
hence "[D k * (n * k * a^(k-1) * (∑m=1..<n. q m * m^(k-1))) = D k * ((a^k-1) * S k n)] (mod n⇧2)"
by (intro cong_mult[OF cong_refl]) (simp_all add: algebra_simps cong_sym_eq)
also have "D k * ((a^k-1) * S k n) = (a^k-1) * (D k * S k n)"
by (simp add: algebra_simps)
also have "[(a^k-1) * (D k * S k n) = (a^k-1) * (N k * int n)] (mod n⇧2)"
using k n by (intro cong_mult cong_refl voronoi_congruence_aux3)
finally have "[n * (k * a^(k-1) * D k * (∑m=1..<n. q m * m^(k-1))) = n * ((a^k-1) * N k)] (mod n⇧2)"
by (simp add: mult_ac)
hence "[k * a^(k-1) * D k * (∑m=1..<n. q m * m^(k-1)) = (a^k-1) * N k] (mod n)"
unfolding power2_eq_square of_nat_mult by (rule cong_mult_cancel) (use n in auto)
thus ?thesis
by (simp add: mult_ac cong_sym_eq q_def)
qed
corollary voronoi_congruence':
fixes k p :: nat and a :: int
assumes k: "even k" "k ≥ 2" and p: "prime p" "¬(p - 1) dvd k" and a: "¬p dvd a" "[a ^ k ≠ 1] (mod p)"
shows "[ℬ k = of_int (k * a^(k-1)) / of_int (a^k - 1) *
of_int (∑m=1..<p. m^(k-1) * ((m * a) div p))] (qmod p)"
proof -
have "¬p dvd D k"
using p k by (auto simp: D_def prime_dvd_bernoulli_denom_iff)
hence "coprime p (D k)"
using p prime_imp_coprime by blast
moreover have "¬p dvd (a ^ k - 1)"
using a cong_iff_dvd_diff by blast
hence "coprime p (a ^ k - 1)"
using p prime_imp_coprime by (metis prime_nat_int_transfer)
moreover have "coprime p a"
using p prime_imp_coprime a by (metis prime_nat_int_transfer)
ultimately have "[of_int (N k) / of_int (D k) =
of_int (int k * a ^ (k-1) * (∑m=1..<p. int m^(k-1) * (int m * a div p))) / of_int (a ^ k - 1)] (qmod p)"
using assms voronoi_congruence[of k p a]
by (subst qcong_fraction_iff) (auto simp: D_def coprime_commute prime_gt_0_nat mult_ac)
thus ?thesis
by (simp add: bernoulli_conv_num_denom mult_ac N_def D_def of_rat_divide)
qed
corollary voronoi_congruence_harvey:
fixes k p :: nat and c a :: int and h :: "nat ⇒ rat"
assumes k: "even k" "k ∈ {2..p-3}" and p: "prime p" "p ≥ 5" and c: "c ∈ {0<..<p}" "[c^k ≠ 1] (mod p)"
assumes a: "[a * c = 1] (mod p)"
defines "h ≡ (λm. of_int (m - c * ((a * m) mod p)) / of_int p + of_int (c - 1) / 2)"
shows "[ℬ k = rat_of_nat k / rat_of_int (1 - c ^ k) * (∑m=1..<p. rat_of_nat m^(k-1) * h m)] (qmod p)"
proof -
have [simp]: "p ≠ 0"
using p by auto
have "odd p"
using p by (intro prime_odd_nat) auto
note [simp del] = div_mult_self3 div_mult_self4 div_mult_self2 div_mult_self1
have [simp]: "D k > 0"
by (auto simp: D_def bernoulli_denom_pos)
have "¬(p - 1) dvd k"
using k p by (auto dest!: dvd_imp_le)
hence [simp]: "coprime (D k) p"
by (subst coprime_commute, intro prime_imp_coprime)
(use p k in ‹auto simp: D_def prime_dvd_bernoulli_denom_iff›)
have "¬p dvd c"
using c p by (auto dest!: zdvd_imp_le)
hence "coprime c p"
using p prime_imp_coprime[of p c] by (auto simp: coprime_commute)
have "coprime a p"
using a coprime_iff_invertible_int by auto
define n where "n = (c * a - 1) div p"
have "[c * a = 1] (mod p)"
using a by (simp add: mult_ac)
hence "p dvd (c * a - 1)"
by (simp add: cong_iff_dvd_diff)
hence n: "c * a = n * p + 1"
unfolding n_def by auto
have "[c * a = 1] (mod int p)"
using a by (simp add: mult_ac)
hence "[(1 ^ k - c ^ k) * N k = ((c * a) ^ k - c ^ k) * N k] (mod p)"
by (intro cong_mult cong_diff cong_refl cong_pow) (auto simp: cong_sym_eq)
also have "((c * a) ^ k - c ^ k) * N k = c ^ k * (a ^ k - 1) * N k"
by (simp add: algebra_simps)
also have "[(a^k-1) * N k = k * a^(k-1) * D k * (∑m=1..<p. m^(k-1) * (m * a div p))] (mod p)"
by (rule voronoi_congruence) (use k p ‹coprime a p› in auto)
hence "[c ^ k * ((a^k-1) * N k) =
c ^ k * (k * a^(k-1) * D k * (∑m=1..<p. m^(k-1) * (m * a div p)))] (mod p)"
by (rule cong_mult[OF cong_refl])
hence "[c ^ k * (a^k-1) * N k =
k * (c ^ k * a^(k-1)) * D k * (∑m=1..<p. m^(k-1) * (m * a div p))] (mod p)"
by (simp add: mult_ac)
also have "c ^ k * a ^ (k - 1) = c * (c * a) ^ (k - 1)"
using k by (cases k) (auto simp: algebra_simps)
also have "[k * (c * (c * a) ^ (k-1)) * D k * (∑m=1..<p. m^(k-1) * (m * a div p)) =
k * (c * 1 ^ (k-1)) * D k * (∑m=1..<p. m^(k-1) * (m * a div p))] (mod p)"
by (intro cong_mult cong_pow cong_refl cong_modular_inverse1) (use a in ‹simp_all add: mult_ac›)
also have "k * (c * 1 ^ (k-1)) * D k * (∑m=1..<p. m^(k-1) * (m * a div p)) =
D k * (k * (∑m=1..<p. m^(k-1) * c * (m * a div p)))"
by (simp add: algebra_simps sum_distrib_left sum_distrib_right)
finally have "[of_int ((1 - c ^ k) * N k) =
of_int (D k * k * (∑m=1..<p. m^(k-1) * c * (m * a div p)))] (qmod p)"
using p by (intro cong_imp_qcong) (auto simp: mult_ac prime_gt_1_nat)
hence "[of_int (1 - c ^ k) * of_int (N k) / of_int (D k) =
of_int k * (∑m=1..<p. of_nat m^(k-1) * (of_int c * of_int (m * a div p)))] (qmod p)"
using p by (subst qcong_divide_of_int_left_iff) (auto simp: mult_ac)
also have "(∑m=1..<p. of_nat m^(k-1) * (of_int c * of_int (m * a div p))) =
(∑m=1..<p. of_nat m^(k-1) * h m + of_int n * of_nat m^k - of_int (c - 1) / 2 * of_nat m^(k-1))"
proof (intro sum.cong, goal_cases)
case (2 m)
have *: "(m * a) div p * p = m * a - ((m * a) mod p)"
by (metis minus_mod_eq_div_mult)
have "c * ((m * a) div p * p) = c * a * m - c * ((m * a) mod p)"
by (subst *) (simp_all add: algebra_simps)
also have "c * a = n * p + 1"
by fact
finally have **: "c * ((m * a) div p) * p = n * m * p + m - c * ((m * a) mod p)"
by (simp add: algebra_simps)
have "of_int (c * ((m * a) div p)) = of_int (n * m * p + m - c * ((m * a) mod p)) / (of_int p :: rat)"
by (subst ** [symmetric]) auto
also have "… = h m + of_int (n * m) - of_int (c - 1) / 2"
by (simp add: h_def field_simps)
finally have ***: "of_int c * of_int (m * a div p) = h m + of_int (n * m) - of_int (c - 1) / 2"
by simp
have "of_nat m^(k-1) * (of_int c * of_int (m * a div p)) =
of_nat m^(k-1) * h m + of_int n * of_nat (m * m^(k-1)) - of_int (c - 1) / 2 * of_nat m^(k-1)"
by (subst ***) (auto simp: algebra_simps)
also have "m * m ^ (k - 1) = m ^ k"
using k by (cases k) auto
finally show ?case
by simp
qed auto
also have "… = (∑m=1..<p. of_nat m^(k-1) * h m) + of_int n * of_int (int (∑m=1..<p. m ^ k)) -
of_int (c-1) / 2 * of_int (int (∑m=1..<p. m^(k-1)))"
by (simp add: sum.distrib sum_subtractf sum_distrib_left sum_distrib_right)
also have "(∑m=1..<p. m ^ k) = S k p"
using k unfolding S_def by (intro sum.mono_neutral_left) auto
also have "(∑m=1..<p. m ^ (k - 1)) = S (k - 1) p"
using k unfolding S_def by (intro sum.mono_neutral_left) auto
also have "[of_int k * ((∑m=1..<p. of_nat m^(k-1) * h m) + of_int n * of_int (int (S k p)) -
of_int (c-1) / 2 * of_int (int (S (k-1) p))) =
of_int k * ((∑m=1..<p. of_nat m^(k-1) * h m) + of_int n * of_int (int 0) -
of_int (c-1) / 2 * of_int (int 0))] (qmod p)"
proof (intro qcong_mult qcong_add qcong_diff cong_imp_qcong qcong_sum qcong_pow qcong_refl cong_int cong_refl)
have "quotient_of (rat_of_int (c - 1) / 2) = (if even c then c - 1 else c div 2, if even c then 2 else 1)"
using c by (intro quotient_of_eqI) (auto elim!: oddE)
thus "coprime (snd (quotient_of (rat_of_int (c - 1) / 2))) (int p)"
using ‹odd p› by auto
next
fix m assume m: "m ∈ {1..<p}"
have "[int m - c * (a * int m mod int p) = int m - c * (a * int m)] (mod p)"
by (intro cong_diff cong_mult cong_refl) auto
also have "c * (a * int m) = (c * a) * int m"
by (simp add: mult_ac)
also have "[int m - (c * a) * int m = int m - 1 * int m] (mod p)"
using a by (intro cong_diff cong_mult cong_refl) (auto simp: mult_ac)
finally have "p dvd int m - c * (a * int m mod int p)"
by (simp add: cong_0_iff)
then obtain d where d: "int m - c * (a * int m mod int p) = int p * d"
by (elim dvdE)
have "h m = of_int (int m - c * (a * int m mod int p)) / of_nat p + of_int (c - 1) / 2"
by (auto simp: h_def)
also note d
also have "rat_of_int (int p * d) / of_nat p = of_int d"
by simp
finally have h_eq: "h m = Rat.Fract (2 * d + c - 1) 2"
by (auto simp: Rat.Fract_of_int_quotient)
have "snd (quotient_of (h m)) dvd 2"
unfolding h_eq quotient_of_Fract using dvd_rat_normalize(2) by simp
with ‹prime p› ‹odd p› have "¬p dvd snd (quotient_of (h m))"
by (metis dvd_trans int_dvd_int_iff of_nat_numeral primes_dvd_imp_eq two_is_prime_nat)
show "coprime (snd (quotient_of (h m))) (int p)"
by (subst coprime_commute, rule prime_imp_coprime)
(use p ‹¬p dvd snd (quotient_of (h m))› in auto)
next
have *: "[S k p = 0] (mod p)" if "¬(p - 1) dvd k" for k
proof -
have "k > 0"
using that by (intro Nat.gr0I) auto
hence "S k p = (∑m=1..<p. m ^ k)"
unfolding S_def by (intro sum.mono_neutral_right) auto
thus ?thesis
using sum_of_powers_mod_prime'[of p k] that p by simp
qed
show "[S k p = 0] (mod p)"
using k by (intro *) (auto dest!: dvd_imp_le)
show "[S (k - 1) p = 0] (mod p)"
using k by (intro *) (auto dest!: dvd_imp_le)
qed (use p in ‹auto simp: prime_gt_1_nat›)
finally have "[rat_of_int (1 - c ^ k) * rat_of_int (N k) / rat_of_int (int (D k)) =
rat_of_nat k * (∑m=1..<p. rat_of_nat m^(k-1) * h m)] (qmod p)"
by simp
moreover have "¬p dvd (1 - c ^ k)"
using c by (auto simp: cong_iff_dvd_diff dvd_diff_commute)
hence "coprime (1 - c ^ k) (int p)"
using prime_imp_coprime[of p "1 - c ^ k"] p by (auto simp: coprime_commute)
ultimately have "[rat_of_int (N k) / rat_of_int (int (D k)) =
rat_of_nat k * (∑m=1..<p. rat_of_nat m^(k-1) * h m) / rat_of_int (1 - c ^ k)] (qmod p)"
using c by (subst qcong_divide_of_int_right_iff) (auto simp: mult_ac)
thus ?thesis
by (simp add: bernoulli_conv_num_denom mult_ac N_def D_def)
qed
corollary voronoi_congruence_harvey':
fixes k p :: nat and g :: nat and h :: "nat ⇒ rat" and a :: int
assumes k: "even k" "k ∈ {2..p-3}" and p: "prime p" "p ≥ 5"
assumes g: "residue_primroot p g" "g ∈ {0<..<p}"
assumes a: "[a * int g = 1] (mod int p)"
defines "h' ≡ (λm. rat_of_int (int m mod p - g * ((a * m) mod p)) / of_int p + of_int (int g - 1) / 2)"
shows "[ℬ k = 2 * of_nat k / of_int (1 - int g ^ k) *
(∑i=1..(p-1) div 2. of_nat (g^(i*(k-1))) * h' (g^i))] (qmod int p)"
proof -
define h :: "nat ⇒ rat" where "h = (λm. of_int (m - g * ((a * m) mod p)) / of_int p + of_int (int g - 1) / 2)"
define m1 where "m1 = g ^ ((p - 1) div 2)"
have cong_m1: "[int m1 = - 1] (mod int p)"
unfolding m1_def using residue_primroot_power_cong_neg1[of p g] g p by simp
from p have [simp]: "p ≠ 0"
by auto
from p have "odd p"
by (intro prime_odd_nat) auto
from g have "coprime g p"
by (auto simp: residue_primroot_def coprime_commute)
have "coprime a p"
using a coprime_iff_invertible_int by auto
have "¬(p - 1) dvd k"
using k p by (auto dest!: dvd_imp_le)
have neq1: "[int g ^ k ≠ 1] (mod p)"
proof -
have "[int g ^ k = 1] (mod p) ⟷ [g ^ k = 1] (mod p)"
using cong_int_iff by force
also have "[g ^ k = 1] (mod p) ⟷ ord p g dvd k"
by (rule ord_divides)
also have "ord p g = totient p"
using g(1) unfolding residue_primroot_def by blast
also have "… = p - 1"
using p by (simp add: totient_prime)
finally show ?thesis
using ‹¬(p - 1) dvd k› by simp
qed
have coprime_h': "coprime (snd (quotient_of (h' (g ^ i)))) (int p)" for i
proof -
define b where "b = (int (g ^ i) mod p - int g * (a * int (g ^ i) mod int p)) div p"
have "[int g * (a * int (g ^ i) mod int p) = int g * (a * int (g ^ i))] (mod p)"
by (intro cong_mult cong_refl) auto
also have "int g * (a * int (g ^ i)) = int g * a * int (g ^ i)"
by (simp add: mult_ac)
also have "[… = 1 * int (g ^ i) mod p] (mod p)"
by (intro cong_mult cong_mod_right) (use a in ‹auto simp: mult_ac›)
finally have "p dvd (int (g ^ i) mod p - int g * (a * int (g ^ i) mod int p))"
by (simp add: cong_iff_dvd_diff dvd_diff_commute)
hence b: "(int (g ^ i) mod p - int g * (a * int (g ^ i) mod int p)) = p * b"
unfolding b_def by simp
have "h' (g ^ i) = Rat.Fract (2 * b + int g - 1) 2"
unfolding h'_def b by (simp add: field_simps Rat.Fract_of_int_quotient)
also have "snd (quotient_of …) dvd 2"
unfolding quotient_of_Fract by (simp add: dvd_rat_normalize(2))
finally have "¬p dvd snd (quotient_of (h' (g ^ i)))" using ‹odd p›
by (metis assms(3) dvd_trans int_dvd_int_iff of_nat_numeral primes_dvd_imp_eq two_is_prime_nat)
with p show ?thesis
using prime_imp_coprime coprime_commute prime_nat_int_transfer by metis
qed
have bij: "bij_betw (λi. g ^ i mod p) {1..p-1} {0<..<p}"
using residue_primroot_is_generator'[of p g] g p
by (simp add: totient_prime totatives_prime prime_gt_Suc_0_nat)
have "[ℬ k = of_nat k / of_int (1 - int g ^ k) * (∑m=1..<p. of_nat m ^ (k-1) * h m)] (qmod p)"
unfolding h_def by (rule voronoi_congruence_harvey) (use k p g neq1 a in simp_all)
also have "(∑m∈{1..<p}. of_nat m ^ (k-1) * h m) = (∑m∈{0<..<p}. of_nat m ^ (k-1) * h (m mod p))"
by (intro sum.cong) auto
also have "(∑m∈{0<..<p}. of_nat m ^ (k-1) * h (m mod p)) =
(∑i=1..p-1. of_nat (g^i mod p) ^ (k-1) * h (g^i mod p mod p))"
using bij by (intro sum.reindex_bij_betw [symmetric])
also have "… = (∑i=1..p-1. of_nat (g^i mod p) ^ (k-1) * h (g^i mod p))"
by simp
also have "… = (∑i=1..p-1. of_nat (g^i mod p) ^ (k-1) * h' (g^i))"
proof (intro sum.cong, goal_cases)
case (2 i)
have "h' (g ^ i) - h (g ^ i mod p mod p) =
of_nat g * of_int (a * int (g ^ i mod p) mod int p - a * int (g ^ i) mod int p) / of_int p"
unfolding h_def h'_def by (simp add: field_simps flip: of_nat_power of_nat_mod)
also have "[a * int (g ^ i mod p) = a * int (g ^ i)] (mod p)"
by (intro cong_mult) (auto simp flip: of_nat_power of_nat_mod intro!: cong_int)
hence "a * int (g ^ i mod p) mod int p = a * int (g ^ i) mod int p"
by (auto simp: Cong.cong_def)
finally show ?case
by simp
qed auto
also have "{1..p-1} = {1..(p-1) div 2} ∪ {(p-1) div 2<..p-1}"
by auto
also have "(∑i∈…. of_nat (g^i mod p) ^ (k-1) * h' (g^i)) =
(∑i=1..(p-1) div 2. of_nat (g^i mod p) ^ (k-1) * h' (g^i)) +
(∑i∈{(p-1) div 2<..p-1}. of_nat (g^i mod p) ^ (k-1) * h' (g^i))"
by (subst sum.union_disjoint) auto
also have "(∑i∈{(p-1) div 2<..p-1}. of_nat (g^i mod p) ^ (k-1) * h' (g^i)) =
(∑i=1..(p-1) div 2. of_nat (g^(i + (p-1) div 2) mod p) ^ (k-1) * h' (g^(i + (p-1) div 2)))"
using ‹odd p›
by (intro sum.reindex_bij_witness[of _ "λi. i + (p-1) div 2" "λi. i - (p-1) div 2"])
(auto elim!: oddE)
also have "[rat_of_nat k / rat_of_int (1 - int g ^ k) *
((∑i=1..(p-1) div 2. of_nat (g^i mod p) ^ (k-1) * h' (g^i)) + …) =
rat_of_nat k / rat_of_int (1 - int g ^ k) * (
(∑i=1..(p-1) div 2. of_nat (g^(i*(k-1))) * h' (g^i)) +
(∑i=1..(p-1) div 2. (-of_int (g^(i*(k-1)))) * (-h' (g^i))))] (qmod p)"
proof (intro qcong_divide_of_int qcong_add qcong_sum qcong_refl qcong_mult)
fix i :: nat
have "rat_of_int (int (g ^ (i + (p - 1) div 2) mod p) ^ (k - 1)) =
of_int ((int g ^ i * m1 mod p) ^ (k - 1))"
by (simp add: power_add m1_def flip: of_nat_power of_nat_mult of_nat_mod)
also have "[… = of_int (- (int g ^ (i * (k - 1))))] (qmod p)"
proof (intro cong_imp_qcong)
have "[(int g ^ i * int m1 mod int p) ^ (k - 1) = (int g ^ i * (-1)) ^ (k - 1)] (mod p)"
by (intro cong_mult cong_pow cong_mod_left cong_refl cong_m1)
also have "(int g ^ i * (-1)) ^ (k - 1) = -(int g ^ (i * (k - 1)))"
using k by (simp add: power_minus' flip: power_mult)
finally show "[(int g ^ i * m1 mod p) ^ (k - 1) = -(int g ^ (i * (k - 1)))] (mod p)" .
qed (use p in auto)
finally show "[rat_of_nat (g ^ (i + (p - 1) div 2) mod p) ^ (k - 1) =
-(rat_of_int (int (g ^ (i * (k - 1)))))] (qmod int p)"
by simp
next
fix i :: nat
have "[int g ^ i * int m1 = int g ^ i * (-1)] (mod p)"
by (intro cong_mult cong_m1 cong_refl)
hence "(int g ^ i * int m1 mod p) = -(int g ^ i) mod p"
by (simp add: Cong.cong_def)
also have nz: "int g ^ i mod p ≠ 0" using ‹coprime g p›
by (metis assms(3) cong_cong_mod_int cong_imp_coprime cong_int_iff cong_refl
coprime_common_divisor_nat coprime_power_left_iff mod_self of_nat_power
power_0 power_one_right prime_factor_nat prime_power_inj zero_neq_one)
hence "-(int g ^ i) mod p = int p - (int g ^ i mod p)"
by (subst zmod_zminus1_eq_if) auto
finally have eq1: "int g ^ i * int m1 mod int p = int p - int g ^ i mod int p" .
have "[a * (int g ^ i * int m1) = a * (int g ^ i * (-1))] (mod p)"
by (intro cong_mult cong_m1 cong_refl)
hence "(a * (int g ^ i * int m1)) mod p = -(a * int g ^ i) mod p"
by (simp add: Cong.cong_def)
also have "(a * int g ^ i) mod p ≠ 0" using ‹coprime a p›
by (metis nz coprime_commute mod_mod_trivial mult_mod_cancel_left mult_not_zero)
hence "-(a * int g ^ i) mod p = int p - (a * int g ^ i mod p)"
by (subst zmod_zminus1_eq_if) auto
finally have eq2: "a * (int g ^ i * int m1) mod int p = int p - a * int g ^ i mod int p"
by (simp add: mult_ac)
have "h' (g ^ (i + (p - 1) div 2)) = h' (g ^ i * m1)"
by (simp add: power_add m1_def)
also have "… = of_int (int p - (int g ^ i mod int p) - int g * (int p - a * int g ^ i mod int p)) /
rat_of_nat p + (rat_of_nat g - 1) / 2"
by (simp add: h'_def eq1 eq2)
also have "… = -h' (g ^ i)"
by (simp add: h'_def field_simps)
finally have "h' (g ^ (i + (p - 1) div 2)) = - h' (g ^ i)"
by simp
moreover have "coprime (snd (quotient_of (- h' (g ^ i)))) (int p)"
by (metis calculation coprime_h')
ultimately show "[h' (g ^ (i + (p - 1) div 2)) = -h' (g ^ i)] (qmod int p)"
by (auto intro!: qcong_refl)
next
fix i :: nat
show "[rat_of_nat (g ^ i mod p) ^ (k - 1) = rat_of_nat (g ^ (i * (k - 1)))] (qmod int p)"
unfolding of_nat_power [symmetric]
proof (rule cong_imp_qcong_of_nat)
have "[(g ^ i mod p) ^ (k - 1) = (g ^ i) ^ (k - 1)] (mod p)"
by (intro cong_pow) auto
also have "(g ^ i) ^ (k - 1) = g ^ (i * (k - 1))"
by (simp add: power_mult)
finally show "[(g ^ i mod p) ^ (k - 1) = g ^ (i * (k - 1))] (mod p)" .
qed (use ‹p ≥ 5› in auto)
next
fix i :: nat
show "coprime (snd (quotient_of (h' (g ^ i)))) (int p)"
using coprime_h'[of i] by auto
next
show "coprime (1 - int g ^ k) (int p)"
by (meson assms(3) cong_iff_dvd_diff dvd_diff_commute neq1 residues_prime.intro
residues_prime.p_coprime_right_int)
thus "1 - int g ^ k ≠ 0"
using ‹p ≥ 5› by fastforce
thus "1 - int g ^ k ≠ 0" .
qed (use ‹p ≥ 5› in auto)
finally show ?thesis
by (simp add: mult_ac)
qed
unbundle no bernoulli_syntax
end
end