(* Title: HOL/GCD.thy Author: Christophe Tabacznyj Author: Lawrence C. Paulson Author: Amine Chaieb Author: Thomas M. Rasmussen Author: Jeremy Avigad Author: Tobias Nipkow This file deals with the functions gcd and lcm. Definitions and lemmas are proved uniformly for the natural numbers and integers. This file combines and revises a number of prior developments. The original theories "GCD" and "Primes" were by Christophe Tabacznyj and Lawrence C. Paulson, based on @{cite davenport92}. They introduced gcd, lcm, and prime for the natural numbers. The original theory "IntPrimes" was by Thomas M. Rasmussen, and extended gcd, lcm, primes to the integers. Amine Chaieb provided another extension of the notions to the integers, and added a number of results to "Primes" and "GCD". IntPrimes also defined and developed the congruence relations on the integers. The notion was extended to the natural numbers by Chaieb. Jeremy Avigad combined all of these, made everything uniform for the natural numbers and the integers, and added a number of new theorems. Tobias Nipkow cleaned up a lot. *) section ‹Greatest common divisor and least common multiple› theory GCD imports Groups_List Code_Numeral begin subsection ‹Abstract bounded quasi semilattices as common foundation› locale bounded_quasi_semilattice = abel_semigroup + fixes top :: 'a ("❙⊤") and bot :: 'a ("❙⊥") and normalize :: "'a ⇒ 'a" assumes idem_normalize [simp]: "a ❙*a = normalize a" and normalize_left_idem [simp]: "normalize a ❙*b = a ❙*b" and normalize_idem [simp]: "normalize (a ❙*b) = a ❙*b" and normalize_top [simp]: "normalize ❙⊤= ❙⊤" and normalize_bottom [simp]: "normalize ❙⊥= ❙⊥" and top_left_normalize [simp]: "❙⊤❙*a = normalize a" and bottom_left_bottom [simp]: "❙⊥❙*a = ❙⊥" begin lemma left_idem [simp]: "a ❙*(a ❙*b) = a ❙*b" using assoc [of a a b, symmetric] by simp lemma right_idem [simp]: "(a ❙*b) ❙*b = a ❙*b" using left_idem [of b a] by (simp add: ac_simps) lemma comp_fun_idem: "comp_fun_idem f" by standard (simp_all add: fun_eq_iff ac_simps) interpretation comp_fun_idem f by (fact comp_fun_idem) lemma top_right_normalize [simp]: "a ❙*❙⊤= normalize a" using top_left_normalize [of a] by (simp add: ac_simps) lemma bottom_right_bottom [simp]: "a ❙*❙⊥= ❙⊥" using bottom_left_bottom [of a] by (simp add: ac_simps) lemma normalize_right_idem [simp]: "a ❙*normalize b = a ❙*b" using normalize_left_idem [of b a] by (simp add: ac_simps) end locale bounded_quasi_semilattice_set = bounded_quasi_semilattice begin interpretation comp_fun_idem f by (fact comp_fun_idem) definition F :: "'a set ⇒ 'a" where eq_fold: "F A = (if finite A then Finite_Set.fold f ❙⊤A else ❙⊥)" lemma infinite [simp]: "infinite A ⟹ F A = ❙⊥" by (simp add: eq_fold) lemma set_eq_fold [code]: "F (set xs) = fold f xs ❙⊤" by (simp add: eq_fold fold_set_fold) lemma empty [simp]: "F {} = ❙⊤" by (simp add: eq_fold) lemma insert [simp]: "F (insert a A) = a ❙*F A" by (cases "finite A") (simp_all add: eq_fold) lemma normalize [simp]: "normalize (F A) = F A" by (induct A rule: infinite_finite_induct) simp_all lemma in_idem: assumes "a ∈ A" shows "a ❙*F A = F A" using assms by (induct A rule: infinite_finite_induct) (auto simp: left_commute [of a]) lemma union: "F (A ∪ B) = F A ❙*F B" by (induct A rule: infinite_finite_induct) (simp_all add: ac_simps) lemma remove: assumes "a ∈ A" shows "F A = a ❙*F (A - {a})" proof - from assms obtain B where "A = insert a B" and "a ∉ B" by (blast dest: mk_disjoint_insert) with assms show ?thesis by simp qed lemma insert_remove: "F (insert a A) = a ❙*F (A - {a})" by (cases "a ∈ A") (simp_all add: insert_absorb remove) lemma subset: assumes "B ⊆ A" shows "F B ❙*F A = F A" using assms by (simp add: union [symmetric] Un_absorb1) end subsection ‹Abstract GCD and LCM› class gcd = zero + one + dvd + fixes gcd :: "'a ⇒ 'a ⇒ 'a" and lcm :: "'a ⇒ 'a ⇒ 'a" class Gcd = gcd + fixes Gcd :: "'a set ⇒ 'a" and Lcm :: "'a set ⇒ 'a" syntax "_GCD1" :: "pttrns ⇒ 'b ⇒ 'b" ("(3GCD _./ _)" [0, 10] 10) "_GCD" :: "pttrn ⇒ 'a set ⇒ 'b ⇒ 'b" ("(3GCD _∈_./ _)" [0, 0, 10] 10) "_LCM1" :: "pttrns ⇒ 'b ⇒ 'b" ("(3LCM _./ _)" [0, 10] 10) "_LCM" :: "pttrn ⇒ 'a set ⇒ 'b ⇒ 'b" ("(3LCM _∈_./ _)" [0, 0, 10] 10) translations "GCD x y. f" ⇌ "GCD x. GCD y. f" "GCD x. f" ⇌ "CONST Gcd (CONST range (λx. f))" "GCD x∈A. f" ⇌ "CONST Gcd ((λx. f) ` A)" "LCM x y. f" ⇌ "LCM x. LCM y. f" "LCM x. f" ⇌ "CONST Lcm (CONST range (λx. f))" "LCM x∈A. f" ⇌ "CONST Lcm ((λx. f) ` A)" class semiring_gcd = normalization_semidom + gcd + assumes gcd_dvd1 [iff]: "gcd a b dvd a" and gcd_dvd2 [iff]: "gcd a b dvd b" and gcd_greatest: "c dvd a ⟹ c dvd b ⟹ c dvd gcd a b" and normalize_gcd [simp]: "normalize (gcd a b) = gcd a b" and lcm_gcd: "lcm a b = normalize (a * b div gcd a b)" begin lemma gcd_greatest_iff [simp]: "a dvd gcd b c ⟷ a dvd b ∧ a dvd c" by (blast intro!: gcd_greatest intro: dvd_trans) lemma gcd_dvdI1: "a dvd c ⟹ gcd a b dvd c" by (rule dvd_trans) (rule gcd_dvd1) lemma gcd_dvdI2: "b dvd c ⟹ gcd a b dvd c" by (rule dvd_trans) (rule gcd_dvd2) lemma dvd_gcdD1: "a dvd gcd b c ⟹ a dvd b" using gcd_dvd1 [of b c] by (blast intro: dvd_trans) lemma dvd_gcdD2: "a dvd gcd b c ⟹ a dvd c" using gcd_dvd2 [of b c] by (blast intro: dvd_trans) lemma gcd_0_left [simp]: "gcd 0 a = normalize a" by (rule associated_eqI) simp_all lemma gcd_0_right [simp]: "gcd a 0 = normalize a" by (rule associated_eqI) simp_all lemma gcd_eq_0_iff [simp]: "gcd a b = 0 ⟷ a = 0 ∧ b = 0" (is "?P ⟷ ?Q") proof assume ?P then have "0 dvd gcd a b" by simp then have "0 dvd a" and "0 dvd b" by (blast intro: dvd_trans)+ then show ?Q by simp next assume ?Q then show ?P by simp qed lemma unit_factor_gcd: "unit_factor (gcd a b) = (if a = 0 ∧ b = 0 then 0 else 1)" proof (cases "gcd a b = 0") case True then show ?thesis by simp next case False have "unit_factor (gcd a b) * normalize (gcd a b) = gcd a b" by (rule unit_factor_mult_normalize) then have "unit_factor (gcd a b) * gcd a b = gcd a b" by simp then have "unit_factor (gcd a b) * gcd a b div gcd a b = gcd a b div gcd a b" by simp with False show ?thesis by simp qed lemma is_unit_gcd_iff [simp]: "is_unit (gcd a b) ⟷ gcd a b = 1" by (cases "a = 0 ∧ b = 0") (auto simp: unit_factor_gcd dest: is_unit_unit_factor) sublocale gcd: abel_semigroup gcd proof fix a b c show "gcd a b = gcd b a" by (rule associated_eqI) simp_all from gcd_dvd1 have "gcd (gcd a b) c dvd a" by (rule dvd_trans) simp moreover from gcd_dvd1 have "gcd (gcd a b) c dvd b" by (rule dvd_trans) simp ultimately have P1: "gcd (gcd a b) c dvd gcd a (gcd b c)" by (auto intro!: gcd_greatest) from gcd_dvd2 have "gcd a (gcd b c) dvd b" by (rule dvd_trans) simp moreover from gcd_dvd2 have "gcd a (gcd b c) dvd c" by (rule dvd_trans) simp ultimately have P2: "gcd a (gcd b c) dvd gcd (gcd a b) c" by (auto intro!: gcd_greatest) from P1 P2 show "gcd (gcd a b) c = gcd a (gcd b c)" by (rule associated_eqI) simp_all qed sublocale gcd: bounded_quasi_semilattice gcd 0 1 normalize proof show "gcd a a = normalize a" for a proof - have "a dvd gcd a a" by (rule gcd_greatest) simp_all then show ?thesis by (auto intro: associated_eqI) qed show "gcd (normalize a) b = gcd a b" for a b using gcd_dvd1 [of "normalize a" b] by (auto intro: associated_eqI) show "gcd 1 a = 1" for a by (rule associated_eqI) simp_all qed simp_all lemma gcd_self: "gcd a a = normalize a" by (fact gcd.idem_normalize) lemma gcd_left_idem: "gcd a (gcd a b) = gcd a b" by (fact gcd.left_idem) lemma gcd_right_idem: "gcd (gcd a b) b = gcd a b" by (fact gcd.right_idem) lemma gcdI: assumes "c dvd a" and "c dvd b" and greatest: "⋀d. d dvd a ⟹ d dvd b ⟹ d dvd c" and "normalize c = c" shows "c = gcd a b" by (rule associated_eqI) (auto simp: assms intro: gcd_greatest) lemma gcd_unique: "d dvd a ∧ d dvd b ∧ normalize d = d ∧ (∀e. e dvd a ∧ e dvd b ⟶ e dvd d) ⟷ d = gcd a b" by rule (auto intro: gcdI simp: gcd_greatest) lemma gcd_dvd_prod: "gcd a b dvd k * b" using mult_dvd_mono [of 1] by auto lemma gcd_proj2_if_dvd: "b dvd a ⟹ gcd a b = normalize b" by (rule gcdI [symmetric]) simp_all lemma gcd_proj1_if_dvd: "a dvd b ⟹ gcd a b = normalize a" by (rule gcdI [symmetric]) simp_all lemma gcd_proj1_iff: "gcd m n = normalize m ⟷ m dvd n" proof assume *: "gcd m n = normalize m" show "m dvd n" proof (cases "m = 0") case True with * show ?thesis by simp next case [simp]: False from * have **: "m = gcd m n * unit_factor m" by (simp add: unit_eq_div2) show ?thesis by (subst **) (simp add: mult_unit_dvd_iff) qed next assume "m dvd n" then show "gcd m n = normalize m" by (rule gcd_proj1_if_dvd) qed lemma gcd_proj2_iff: "gcd m n = normalize n ⟷ n dvd m" using gcd_proj1_iff [of n m] by (simp add: ac_simps) lemma gcd_mult_left: "gcd (c * a) (c * b) = normalize (c * gcd a b)" proof (cases "c = 0") case True then show ?thesis by simp next case False then have *: "c * gcd a b dvd gcd (c * a) (c * b)" by (auto intro: gcd_greatest) moreover from False * have "gcd (c * a) (c * b) dvd c * gcd a b" by (metis div_dvd_iff_mult dvd_mult_left gcd_dvd1 gcd_dvd2 gcd_greatest mult_commute) ultimately have "normalize (gcd (c * a) (c * b)) = normalize (c * gcd a b)" by (auto intro: associated_eqI) then show ?thesis by (simp add: normalize_mult) qed lemma gcd_mult_right: "gcd (a * c) (b * c) = normalize (gcd b a * c)" using gcd_mult_left [of c a b] by (simp add: ac_simps) lemma dvd_lcm1 [iff]: "a dvd lcm a b" by (metis div_mult_swap dvd_mult2 dvd_normalize_iff dvd_refl gcd_dvd2 lcm_gcd) lemma dvd_lcm2 [iff]: "b dvd lcm a b" by (metis dvd_div_mult dvd_mult dvd_normalize_iff dvd_refl gcd_dvd1 lcm_gcd) lemma dvd_lcmI1: "a dvd b ⟹ a dvd lcm b c" by (rule dvd_trans) (assumption, blast) lemma dvd_lcmI2: "a dvd c ⟹ a dvd lcm b c" by (rule dvd_trans) (assumption, blast) lemma lcm_dvdD1: "lcm a b dvd c ⟹ a dvd c" using dvd_lcm1 [of a b] by (blast intro: dvd_trans) lemma lcm_dvdD2: "lcm a b dvd c ⟹ b dvd c" using dvd_lcm2 [of a b] by (blast intro: dvd_trans) lemma lcm_least: assumes "a dvd c" and "b dvd c" shows "lcm a b dvd c" proof (cases "c = 0") case True then show ?thesis by simp next case False then have *: "is_unit (unit_factor c)" by simp show ?thesis proof (cases "gcd a b = 0") case True with assms show ?thesis by simp next case False have "a * b dvd normalize (c * gcd a b)" using assms by (subst gcd_mult_left [symmetric]) (auto intro!: gcd_greatest simp: mult_ac) with False have "(a * b div gcd a b) dvd c" by (subst div_dvd_iff_mult) auto thus ?thesis by (simp add: lcm_gcd) qed qed lemma lcm_least_iff [simp]: "lcm a b dvd c ⟷ a dvd c ∧ b dvd c" by (blast intro!: lcm_least intro: dvd_trans) lemma normalize_lcm [simp]: "normalize (lcm a b) = lcm a b" by (simp add: lcm_gcd dvd_normalize_div) lemma lcm_0_left [simp]: "lcm 0 a = 0" by (simp add: lcm_gcd) lemma lcm_0_right [simp]: "lcm a 0 = 0" by (simp add: lcm_gcd) lemma lcm_eq_0_iff: "lcm a b = 0 ⟷ a = 0 ∨ b = 0" (is "?P ⟷ ?Q") proof assume ?P then have "0 dvd lcm a b" by simp also have "lcm a b dvd (a * b)" by simp finally show ?Q by auto next assume ?Q then show ?P by auto qed lemma zero_eq_lcm_iff: "0 = lcm a b ⟷ a = 0 ∨ b = 0" using lcm_eq_0_iff[of a b] by auto lemma lcm_eq_1_iff [simp]: "lcm a b = 1 ⟷ is_unit a ∧ is_unit b" by (auto intro: associated_eqI) lemma unit_factor_lcm: "unit_factor (lcm a b) = (if a = 0 ∨ b = 0 then 0 else 1)" using lcm_eq_0_iff[of a b] by (cases "lcm a b = 0") (auto simp: lcm_gcd) sublocale lcm: abel_semigroup lcm proof fix a b c show "lcm a b = lcm b a" by (simp add: lcm_gcd ac_simps normalize_mult dvd_normalize_div) have "lcm (lcm a b) c dvd lcm a (lcm b c)" and "lcm a (lcm b c) dvd lcm (lcm a b) c" by (auto intro: lcm_least dvd_trans [of b "lcm b c" "lcm a (lcm b c)"] dvd_trans [of c "lcm b c" "lcm a (lcm b c)"] dvd_trans [of a "lcm a b" "lcm (lcm a b) c"] dvd_trans [of b "lcm a b" "lcm (lcm a b) c"]) then show "lcm (lcm a b) c = lcm a (lcm b c)" by (rule associated_eqI) simp_all qed sublocale lcm: bounded_quasi_semilattice lcm 1 0 normalize proof show "lcm a a = normalize a" for a proof - have "lcm a a dvd a" by (rule lcm_least) simp_all then show ?thesis by (auto intro: associated_eqI) qed show "lcm (normalize a) b = lcm a b" for a b using dvd_lcm1 [of "normalize a" b] unfolding normalize_dvd_iff by (auto intro: associated_eqI) show "lcm 1 a = normalize a" for a by (rule associated_eqI) simp_all qed simp_all lemma lcm_self: "lcm a a = normalize a" by (fact lcm.idem_normalize) lemma lcm_left_idem: "lcm a (lcm a b) = lcm a b" by (fact lcm.left_idem) lemma lcm_right_idem: "lcm (lcm a b) b = lcm a b" by (fact lcm.right_idem) lemma gcd_lcm: assumes "a ≠ 0" and "b ≠ 0" shows "gcd a b = normalize (a * b div lcm a b)" proof - from assms have [simp]: "a * b div gcd a b ≠ 0" by (subst dvd_div_eq_0_iff) auto let ?u = "unit_factor (a * b div gcd a b)" have "gcd a b * normalize (a * b div gcd a b) = gcd a b * ((a * b div gcd a b) * (1 div ?u))" by simp also have "… = a * b div ?u" by (subst mult.assoc [symmetric]) auto also have "… dvd a * b" by (subst div_unit_dvd_iff) auto finally have "gcd a b dvd ((a * b) div lcm a b)" by (intro dvd_mult_imp_div) (auto simp: lcm_gcd) moreover have "a * b div lcm a b dvd a" and "a * b div lcm a b dvd b" using assms by (subst div_dvd_iff_mult; simp add: lcm_eq_0_iff mult.commute[of b "lcm a b"])+ ultimately have "normalize (gcd a b) = normalize (a * b div lcm a b)" apply - apply (rule associated_eqI) using assms apply (auto simp: div_dvd_iff_mult zero_eq_lcm_iff) done thus ?thesis by simp qed lemma lcm_1_left: "lcm 1 a = normalize a" by (fact lcm.top_left_normalize) lemma lcm_1_right: "lcm a 1 = normalize a" by (fact lcm.top_right_normalize) lemma lcm_mult_left: "lcm (c * a) (c * b) = normalize (c * lcm a b)" proof (cases "c = 0") case True then show ?thesis by simp next case False then have *: "lcm (c * a) (c * b) dvd c * lcm a b" by (auto intro: lcm_least) moreover have "lcm a b dvd lcm (c * a) (c * b) div c" by (intro lcm_least) (auto intro!: dvd_mult_imp_div simp: mult_ac) hence "c * lcm a b dvd lcm (c * a) (c * b)" using False by (subst (asm) dvd_div_iff_mult) (auto simp: mult_ac intro: dvd_lcmI1) ultimately have "normalize (lcm (c * a) (c * b)) = normalize (c * lcm a b)" by (auto intro: associated_eqI) then show ?thesis by (simp add: normalize_mult) qed lemma lcm_mult_right: "lcm (a * c) (b * c) = normalize (lcm b a * c)" using lcm_mult_left [of c a b] by (simp add: ac_simps) lemma lcm_mult_unit1: "is_unit a ⟹ lcm (b * a) c = lcm b c" by (rule associated_eqI) (simp_all add: mult_unit_dvd_iff dvd_lcmI1) lemma lcm_mult_unit2: "is_unit a ⟹ lcm b (c * a) = lcm b c" using lcm_mult_unit1 [of a c b] by (simp add: ac_simps) lemma lcm_div_unit1: "is_unit a ⟹ lcm (b div a) c = lcm b c" by (erule is_unitE [of _ b]) (simp add: lcm_mult_unit1) lemma lcm_div_unit2: "is_unit a ⟹ lcm b (c div a) = lcm b c" by (erule is_unitE [of _ c]) (simp add: lcm_mult_unit2) lemma normalize_lcm_left: "lcm (normalize a) b = lcm a b" by (fact lcm.normalize_left_idem) lemma normalize_lcm_right: "lcm a (normalize b) = lcm a b" by (fact lcm.normalize_right_idem) lemma comp_fun_idem_gcd: "comp_fun_idem gcd" by standard (simp_all add: fun_eq_iff ac_simps) lemma comp_fun_idem_lcm: "comp_fun_idem lcm" by standard (simp_all add: fun_eq_iff ac_simps) lemma gcd_dvd_antisym: "gcd a b dvd gcd c d ⟹ gcd c d dvd gcd a b ⟹ gcd a b = gcd c d" proof (rule gcdI) assume *: "gcd a b dvd gcd c d" and **: "gcd c d dvd gcd a b" have "gcd c d dvd c" by simp with * show "gcd a b dvd c" by (rule dvd_trans) have "gcd c d dvd d" by simp with * show "gcd a b dvd d" by (rule dvd_trans) show "normalize (gcd a b) = gcd a b" by simp fix l assume "l dvd c" and "l dvd d" then have "l dvd gcd c d" by (rule gcd_greatest) from this and ** show "l dvd gcd a b" by (rule dvd_trans) qed declare unit_factor_lcm [simp] lemma lcmI: assumes "a dvd c" and "b dvd c" and "⋀d. a dvd d ⟹ b dvd d ⟹ c dvd d" and "normalize c = c" shows "c = lcm a b" by (rule associated_eqI) (auto simp: assms intro: lcm_least) lemma gcd_dvd_lcm [simp]: "gcd a b dvd lcm a b" using gcd_dvd2 by (rule dvd_lcmI2) lemmas lcm_0 = lcm_0_right lemma lcm_unique: "a dvd d ∧ b dvd d ∧ normalize d = d ∧ (∀e. a dvd e ∧ b dvd e ⟶ d dvd e) ⟷ d = lcm a b" by rule (auto intro: lcmI simp: lcm_least lcm_eq_0_iff) lemma lcm_proj1_if_dvd: assumes "b dvd a" shows "lcm a b = normalize a" proof - have "normalize (lcm a b) = normalize a" by (rule associatedI) (use assms in auto) thus ?thesis by simp qed lemma lcm_proj2_if_dvd: "a dvd b ⟹ lcm a b = normalize b" using lcm_proj1_if_dvd [of a b] by (simp add: ac_simps) lemma lcm_proj1_iff: "lcm m n = normalize m ⟷ n dvd m" proof assume *: "lcm m n = normalize m" show "n dvd m" proof (cases "m = 0") case True then show ?thesis by simp next case [simp]: False from * have **: "m = lcm m n * unit_factor m" by (simp add: unit_eq_div2) show ?thesis by (subst **) simp qed next assume "n dvd m" then show "lcm m n = normalize m" by (rule lcm_proj1_if_dvd) qed lemma lcm_proj2_iff: "lcm m n = normalize n ⟷ m dvd n" using lcm_proj1_iff [of n m] by (simp add: ac_simps) lemma gcd_mono: "a dvd c ⟹ b dvd d ⟹ gcd a b dvd gcd c d" by (simp add: gcd_dvdI1 gcd_dvdI2) lemma lcm_mono: "a dvd c ⟹ b dvd d ⟹ lcm a b dvd lcm c d" by (simp add: dvd_lcmI1 dvd_lcmI2) lemma dvd_productE: assumes "p dvd a * b" obtains x y where "p = x * y" "x dvd a" "y dvd b" proof (cases "a = 0") case True thus ?thesis by (intro that[of p 1]) simp_all next case False define x y where "x = gcd a p" and "y = p div x" have "p = x * y" by (simp add: x_def y_def) moreover have "x dvd a" by (simp add: x_def) moreover from assms have "p dvd gcd (b * a) (b * p)" by (intro gcd_greatest) (simp_all add: mult.commute) hence "p dvd b * gcd a p" by (subst (asm) gcd_mult_left) auto with False have "y dvd b" by (simp add: x_def y_def div_dvd_iff_mult assms) ultimately show ?thesis by (rule that) qed lemma gcd_mult_unit1: assumes "is_unit a" shows "gcd (b * a) c = gcd b c" proof - have "gcd (b * a) c dvd b" using assms dvd_mult_unit_iff by blast then show ?thesis by (rule gcdI) simp_all qed lemma gcd_mult_unit2: "is_unit a ⟹ gcd b (c * a) = gcd b c" using gcd.commute gcd_mult_unit1 by auto lemma gcd_div_unit1: "is_unit a ⟹ gcd (b div a) c = gcd b c" by (erule is_unitE [of _ b]) (simp add: gcd_mult_unit1) lemma gcd_div_unit2: "is_unit a ⟹ gcd b (c div a) = gcd b c" by (erule is_unitE [of _ c]) (simp add: gcd_mult_unit2) lemma normalize_gcd_left: "gcd (normalize a) b = gcd a b" by (fact gcd.normalize_left_idem) lemma normalize_gcd_right: "gcd a (normalize b) = gcd a b" by (fact gcd.normalize_right_idem) lemma gcd_add1 [simp]: "gcd (m + n) n = gcd m n" by (rule gcdI [symmetric]) (simp_all add: dvd_add_left_iff) lemma gcd_add2 [simp]: "gcd m (m + n) = gcd m n" using gcd_add1 [of n m] by (simp add: ac_simps) lemma gcd_add_mult: "gcd m (k * m + n) = gcd m n" by (rule gcdI [symmetric]) (simp_all add: dvd_add_right_iff) end class ring_gcd = comm_ring_1 + semiring_gcd begin lemma gcd_neg1 [simp]: "gcd (-a) b = gcd a b" by (rule sym, rule gcdI) (simp_all add: gcd_greatest) lemma gcd_neg2 [simp]: "gcd a (-b) = gcd a b" by (rule sym, rule gcdI) (simp_all add: gcd_greatest) lemma gcd_neg_numeral_1 [simp]: "gcd (- numeral n) a = gcd (numeral n) a" by (fact gcd_neg1) lemma gcd_neg_numeral_2 [simp]: "gcd a (- numeral n) = gcd a (numeral n)" by (fact gcd_neg2) lemma gcd_diff1: "gcd (m - n) n = gcd m n" by (subst diff_conv_add_uminus, subst gcd_neg2[symmetric], subst gcd_add1, simp) lemma gcd_diff2: "gcd (n - m) n = gcd m n" by (subst gcd_neg1[symmetric]) (simp only: minus_diff_eq gcd_diff1) lemma lcm_neg1 [simp]: "lcm (-a) b = lcm a b" by (rule sym, rule lcmI) (simp_all add: lcm_least lcm_eq_0_iff) lemma lcm_neg2 [simp]: "lcm a (-b) = lcm a b" by (rule sym, rule lcmI) (simp_all add: lcm_least lcm_eq_0_iff) lemma lcm_neg_numeral_1 [simp]: "lcm (- numeral n) a = lcm (numeral n) a" by (fact lcm_neg1) lemma lcm_neg_numeral_2 [simp]: "lcm a (- numeral n) = lcm a (numeral n)" by (fact lcm_neg2) end class semiring_Gcd = semiring_gcd + Gcd + assumes Gcd_dvd: "a ∈ A ⟹ Gcd A dvd a" and Gcd_greatest: "(⋀b. b ∈ A ⟹ a dvd b) ⟹ a dvd Gcd A" and normalize_Gcd [simp]: "normalize (Gcd A) = Gcd A" assumes dvd_Lcm: "a ∈ A ⟹ a dvd Lcm A" and Lcm_least: "(⋀b. b ∈ A ⟹ b dvd a) ⟹ Lcm A dvd a" and normalize_Lcm [simp]: "normalize (Lcm A) = Lcm A" begin lemma Lcm_Gcd: "Lcm A = Gcd {b. ∀a∈A. a dvd b}" by (rule associated_eqI) (auto intro: Gcd_dvd dvd_Lcm Gcd_greatest Lcm_least) lemma Gcd_Lcm: "Gcd A = Lcm {b. ∀a∈A. b dvd a}" by (rule associated_eqI) (auto intro: Gcd_dvd dvd_Lcm Gcd_greatest Lcm_least) lemma Gcd_empty [simp]: "Gcd {} = 0" by (rule dvd_0_left, rule Gcd_greatest) simp lemma Lcm_empty [simp]: "Lcm {} = 1" by (auto intro: associated_eqI Lcm_least) lemma Gcd_insert [simp]: "Gcd (insert a A) = gcd a (Gcd A)" proof - have "Gcd (insert a A) dvd gcd a (Gcd A)" by (auto intro: Gcd_dvd Gcd_greatest) moreover have "gcd a (Gcd A) dvd Gcd (insert a A)" proof (rule Gcd_greatest) fix b assume "b ∈ insert a A" then show "gcd a (Gcd A) dvd b" proof assume "b = a" then show ?thesis by simp next assume "b ∈ A" then have "Gcd A dvd b" by (rule Gcd_dvd) moreover have "gcd a (Gcd A) dvd Gcd A" by simp ultimately show ?thesis by (blast intro: dvd_trans) qed qed ultimately show ?thesis by (auto intro: associated_eqI) qed lemma Lcm_insert [simp]: "Lcm (insert a A) = lcm a (Lcm A)" proof (rule sym) have "lcm a (Lcm A) dvd Lcm (insert a A)" by (auto intro: dvd_Lcm Lcm_least) moreover have "Lcm (insert a A) dvd lcm a (Lcm A)" proof (rule Lcm_least) fix b assume "b ∈ insert a A" then show "b dvd lcm a (Lcm A)" proof assume "b = a" then show ?thesis by simp next assume "b ∈ A" then have "b dvd Lcm A" by (rule dvd_Lcm) moreover have "Lcm A dvd lcm a (Lcm A)" by simp ultimately show ?thesis by (blast intro: dvd_trans) qed qed ultimately show "lcm a (Lcm A) = Lcm (insert a A)" by (rule associated_eqI) (simp_all add: lcm_eq_0_iff) qed lemma LcmI: assumes "⋀a. a ∈ A ⟹ a dvd b" and "⋀c. (⋀a. a ∈ A ⟹ a dvd c) ⟹ b dvd c" and "normalize b = b" shows "b = Lcm A" by (rule associated_eqI) (auto simp: assms dvd_Lcm intro: Lcm_least) lemma Lcm_subset: "A ⊆ B ⟹ Lcm A dvd Lcm B" by (blast intro: Lcm_least dvd_Lcm) lemma Lcm_Un: "Lcm (A ∪ B) = lcm (Lcm A) (Lcm B)" proof - have "⋀d. ⟦Lcm A dvd d; Lcm B dvd d⟧ ⟹ Lcm (A ∪ B) dvd d" by (meson UnE Lcm_least dvd_Lcm dvd_trans) then show ?thesis by (meson Lcm_subset lcm_unique normalize_Lcm sup.cobounded1 sup.cobounded2) qed lemma Gcd_0_iff [simp]: "Gcd A = 0 ⟷ A ⊆ {0}" (is "?P ⟷ ?Q") proof assume ?P show ?Q proof fix a assume "a ∈ A" then have "Gcd A dvd a" by (rule Gcd_dvd) with ‹?P› have "a = 0" by simp then show "a ∈ {0}" by simp qed next assume ?Q have "0 dvd Gcd A" proof (rule Gcd_greatest) fix a assume "a ∈ A" with ‹?Q› have "a = 0" by auto then show "0 dvd a" by simp qed then show ?P by simp qed lemma Lcm_1_iff [simp]: "Lcm A = 1 ⟷ (∀a∈A. is_unit a)" (is "?P ⟷ ?Q") proof assume ?P show ?Q proof fix a assume "a ∈ A" then have "a dvd Lcm A" by (rule dvd_Lcm) with ‹?P› show "is_unit a" by simp qed next assume ?Q then have "is_unit (Lcm A)" by (blast intro: Lcm_least) then have "normalize (Lcm A) = 1" by (rule is_unit_normalize) then show ?P by simp qed lemma unit_factor_Lcm: "unit_factor (Lcm A) = (if Lcm A = 0 then 0 else 1)" proof (cases "Lcm A = 0") case True then show ?thesis by simp next case False with unit_factor_normalize have "unit_factor (normalize (Lcm A)) = 1" by blast with False show ?thesis by simp qed lemma unit_factor_Gcd: "unit_factor (Gcd A) = (if Gcd A = 0 then 0 else 1)" by (simp add: Gcd_Lcm unit_factor_Lcm) lemma GcdI: assumes "⋀a. a ∈ A ⟹ b dvd a" and "⋀c. (⋀a. a ∈ A ⟹ c dvd a) ⟹ c dvd b" and "normalize b = b" shows "b = Gcd A" by (rule associated_eqI) (auto simp: assms Gcd_dvd intro: Gcd_greatest) lemma Gcd_eq_1_I: assumes "is_unit a" and "a ∈ A" shows "Gcd A = 1" proof - from assms have "is_unit (Gcd A)" by (blast intro: Gcd_dvd dvd_unit_imp_unit) then have "normalize (Gcd A) = 1" by (rule is_unit_normalize) then show ?thesis by simp qed lemma Lcm_eq_0_I: assumes "0 ∈ A" shows "Lcm A = 0" proof - from assms have "0 dvd Lcm A" by (rule dvd_Lcm) then show ?thesis by simp qed lemma Gcd_UNIV [simp]: "Gcd UNIV = 1" using dvd_refl by (rule Gcd_eq_1_I) simp lemma Lcm_UNIV [simp]: "Lcm UNIV = 0" by (rule Lcm_eq_0_I) simp lemma Lcm_0_iff: assumes "finite A" shows "Lcm A = 0 ⟷ 0 ∈ A" proof (cases "A = {}") case True then show ?thesis by simp next case False with assms show ?thesis by (induct A rule: finite_ne_induct) (auto simp: lcm_eq_0_iff) qed lemma Gcd_image_normalize [simp]: "Gcd (normalize ` A) = Gcd A" proof - have "Gcd (normalize ` A) dvd a" if "a ∈ A" for a proof - from that obtain B where "A = insert a B" by blast moreover have "gcd (normalize a) (Gcd (normalize ` B)) dvd normalize a" by (rule gcd_dvd1) ultimately show "Gcd (normalize ` A) dvd a" by simp qed then have "Gcd (normalize ` A) dvd Gcd A" and "Gcd A dvd Gcd (normalize ` A)" by (auto intro!: Gcd_greatest intro: Gcd_dvd) then show ?thesis by (auto intro: associated_eqI) qed lemma Gcd_eqI: assumes "normalize a = a" assumes "⋀b. b ∈ A ⟹ a dvd b" and "⋀c. (⋀b. b ∈ A ⟹ c dvd b) ⟹ c dvd a" shows "Gcd A = a" using assms by (blast intro: associated_eqI Gcd_greatest Gcd_dvd normalize_Gcd) lemma dvd_GcdD: "x dvd Gcd A ⟹ y ∈ A ⟹ x dvd y" using Gcd_dvd dvd_trans by blast lemma dvd_Gcd_iff: "x dvd Gcd A ⟷ (∀y∈A. x dvd y)" by (blast dest: dvd_GcdD intro: Gcd_greatest) lemma Gcd_mult: "Gcd ((*) c ` A) = normalize (c * Gcd A)" proof (cases "c = 0") case True then show ?thesis by auto next case [simp]: False have "Gcd ((*) c ` A) div c dvd Gcd A" by (intro Gcd_greatest, subst div_dvd_iff_mult) (auto intro!: Gcd_greatest Gcd_dvd simp: mult.commute[of _ c]) then have "Gcd ((*) c ` A) dvd c * Gcd A" by (subst (asm) div_dvd_iff_mult) (auto intro: Gcd_greatest simp: mult_ac) moreover have "c * Gcd A dvd Gcd ((*) c ` A)" by (intro Gcd_greatest) (auto intro: mult_dvd_mono Gcd_dvd) ultimately have "normalize (Gcd ((*) c ` A)) = normalize (c * Gcd A)" by (rule associatedI) then show ?thesis by simp qed lemma Lcm_eqI: assumes "normalize a = a" and "⋀b. b ∈ A ⟹ b dvd a" and "⋀c. (⋀b. b ∈ A ⟹ b dvd c) ⟹ a dvd c" shows "Lcm A = a" using assms by (blast intro: associated_eqI Lcm_least dvd_Lcm normalize_Lcm) lemma Lcm_dvdD: "Lcm A dvd x ⟹ y ∈ A ⟹ y dvd x" using dvd_Lcm dvd_trans by blast lemma Lcm_dvd_iff: "Lcm A dvd x ⟷ (∀y∈A. y dvd x)" by (blast dest: Lcm_dvdD intro: Lcm_least) lemma Lcm_mult: assumes "A ≠ {}" shows "Lcm ((*) c ` A) = normalize (c * Lcm A)" proof (cases "c = 0") case True with assms have "(*) c ` A = {0}" by auto with True show ?thesis by auto next case [simp]: False from assms obtain x where x: "x ∈ A" by blast have "c dvd c * x" by simp also from x have "c * x dvd Lcm ((*) c ` A)" by (intro dvd_Lcm) auto finally have dvd: "c dvd Lcm ((*) c ` A)" . moreover have "Lcm A dvd Lcm ((*) c ` A) div c" by (intro Lcm_least dvd_mult_imp_div) (auto intro!: Lcm_least dvd_Lcm simp: mult.commute[of _ c]) ultimately have "c * Lcm A dvd Lcm ((*) c ` A)" by auto moreover have "Lcm ((*) c ` A) dvd c * Lcm A" by (intro Lcm_least) (auto intro: mult_dvd_mono dvd_Lcm) ultimately have "normalize (c * Lcm A) = normalize (Lcm ((*) c ` A))" by (rule associatedI) then show ?thesis by simp qed lemma Lcm_no_units: "Lcm A = Lcm (A - {a. is_unit a})" proof - have "(A - {a. is_unit a}) ∪ {a∈A. is_unit a} = A" by blast then have "Lcm A = lcm (Lcm (A - {a. is_unit a})) (Lcm {a∈A. is_unit a})" by (simp add: Lcm_Un [symmetric]) also have "Lcm {a∈A. is_unit a} = 1" by simp finally show ?thesis by simp qed lemma Lcm_0_iff': "Lcm A = 0 ⟷ (∄l. l ≠ 0 ∧ (∀a∈A. a dvd l))" by (metis Lcm_least dvd_0_left dvd_Lcm) lemma Lcm_no_multiple: "(∀m. m ≠ 0 ⟶ (∃a∈A. ¬ a dvd m)) ⟹ Lcm A = 0" by (auto simp: Lcm_0_iff') lemma Lcm_singleton [simp]: "Lcm {a} = normalize a" by simp lemma Lcm_2 [simp]: "Lcm {a, b} = lcm a b" by simp lemma Gcd_1: "1 ∈ A ⟹ Gcd A = 1" by (auto intro!: Gcd_eq_1_I) lemma Gcd_singleton [simp]: "Gcd {a} = normalize a" by simp lemma Gcd_2 [simp]: "Gcd {a, b} = gcd a b" by simp lemma Gcd_mono: assumes "⋀x. x ∈ A ⟹ f x dvd g x" shows "(GCD x∈A. f x) dvd (GCD x∈A. g x)" proof (intro Gcd_greatest, safe) fix x assume "x ∈ A" hence "(GCD x∈A. f x) dvd f x" by (intro Gcd_dvd) auto also have "f x dvd g x" using ‹x ∈ A› assms by blast finally show "(GCD x∈A. f x) dvd …" . qed lemma Lcm_mono: assumes "⋀x. x ∈ A ⟹ f x dvd g x" shows "(LCM x∈A. f x) dvd (LCM x∈A. g x)" proof (intro Lcm_least, safe) fix x assume "x ∈ A" hence "f x dvd g x" by (rule assms) also have "g x dvd (LCM x∈A. g x)" using ‹x ∈ A› by (intro dvd_Lcm) auto finally show "f x dvd …" . qed end subsection ‹An aside: GCD and LCM on finite sets for incomplete gcd rings› context semiring_gcd begin sublocale Gcd_fin: bounded_quasi_semilattice_set gcd 0 1 normalize defines Gcd_fin ("Gcd⇩_{f}⇩_{i}⇩_{n}") = "Gcd_fin.F :: 'a set ⇒ 'a" .. abbreviation gcd_list :: "'a list ⇒ 'a" where "gcd_list xs ≡ Gcd⇩_{f}⇩_{i}⇩_{n}(set xs)" sublocale Lcm_fin: bounded_quasi_semilattice_set lcm 1 0 normalize defines Lcm_fin ("Lcm⇩_{f}⇩_{i}⇩_{n}") = Lcm_fin.F .. abbreviation lcm_list :: "'a list ⇒ 'a" where "lcm_list xs ≡ Lcm⇩_{f}⇩_{i}⇩_{n}(set xs)" lemma Gcd_fin_dvd: "a ∈ A ⟹ Gcd⇩_{f}⇩_{i}⇩_{n}A dvd a" by (induct A rule: infinite_finite_induct) (auto intro: dvd_trans) lemma dvd_Lcm_fin: "a ∈ A ⟹ a dvd Lcm⇩_{f}⇩_{i}⇩_{n}A" by (induct A rule: infinite_finite_induct) (auto intro: dvd_trans) lemma Gcd_fin_greatest: "a dvd Gcd⇩_{f}⇩_{i}⇩_{n}A" if "finite A" and "⋀b. b ∈ A ⟹ a dvd b" using that by (induct A) simp_all lemma Lcm_fin_least: "Lcm⇩_{f}⇩_{i}⇩_{n}A dvd a" if "finite A" and "⋀b. b ∈ A ⟹ b dvd a" using that by (induct A) simp_all lemma gcd_list_greatest: "a dvd gcd_list bs" if "⋀b. b ∈ set bs ⟹ a dvd b" by (rule Gcd_fin_greatest) (simp_all add: that) lemma lcm_list_least: "lcm_list bs dvd a" if "⋀b. b ∈ set bs ⟹ b dvd a" by (rule Lcm_fin_least) (simp_all add: that) lemma dvd_Gcd_fin_iff: "b dvd Gcd⇩_{f}⇩_{i}⇩_{n}A ⟷ (∀a∈A. b dvd a)" if "finite A" using that by (auto intro: Gcd_fin_greatest Gcd_fin_dvd dvd_trans [of b "Gcd⇩_{f}⇩_{i}⇩_{n}A"]) lemma dvd_gcd_list_iff: "b dvd gcd_list xs ⟷ (∀a∈set xs. b dvd a)" by (simp add: dvd_Gcd_fin_iff) lemma Lcm_fin_dvd_iff: "Lcm⇩_{f}⇩_{i}⇩_{n}A dvd b ⟷ (∀a∈A. a dvd b)" if "finite A" using that by (auto intro: Lcm_fin_least dvd_Lcm_fin dvd_trans [of _ "Lcm⇩_{f}⇩_{i}⇩_{n}A" b]) lemma lcm_list_dvd_iff: "lcm_list xs dvd b ⟷ (∀a∈set xs. a dvd b)" by (simp add: Lcm_fin_dvd_iff) lemma Gcd_fin_mult: "Gcd⇩_{f}⇩_{i}⇩_{n}(image (times b) A) = normalize (b * Gcd⇩_{f}⇩_{i}⇩_{n}A)" if "finite A" using that by induction (auto simp: gcd_mult_left) lemma Lcm_fin_mult: "Lcm⇩_{f}⇩_{i}⇩_{n}(image (times b) A) = normalize (b * Lcm⇩_{f}⇩_{i}⇩_{n}A)" if "A ≠ {}" proof (cases "b = 0") case True moreover from that have "times 0 ` A = {0}" by auto ultimately show ?thesis by simp next case False show ?thesis proof (cases "finite A") case False moreover have "inj_on (times b) A" using ‹b ≠ 0› by (rule inj_on_mult) ultimately have "infinite (times b ` A)" by (simp add: finite_image_iff) with False show ?thesis by simp next case True then show ?thesis using that by (induct A rule: finite_ne_induct) (auto simp: lcm_mult_left) qed qed lemma unit_factor_Gcd_fin: "unit_factor (Gcd⇩_{f}⇩_{i}⇩_{n}A) = of_bool (Gcd⇩_{f}⇩_{i}⇩_{n}A ≠ 0)" by (rule normalize_idem_imp_unit_factor_eq) simp lemma unit_factor_Lcm_fin: "unit_factor (Lcm⇩_{f}⇩_{i}⇩_{n}A) = of_bool (Lcm⇩_{f}⇩_{i}⇩_{n}A ≠ 0)" by (rule normalize_idem_imp_unit_factor_eq) simp lemma is_unit_Gcd_fin_iff [simp]: "is_unit (Gcd⇩_{f}⇩_{i}⇩_{n}A) ⟷ Gcd⇩_{f}⇩_{i}⇩_{n}A = 1" by (rule normalize_idem_imp_is_unit_iff) simp lemma is_unit_Lcm_fin_iff [simp]: "is_unit (Lcm⇩_{f}⇩_{i}⇩_{n}A) ⟷ Lcm⇩_{f}⇩_{i}⇩_{n}A = 1" by (rule normalize_idem_imp_is_unit_iff) simp lemma Gcd_fin_0_iff: "Gcd⇩_{f}⇩_{i}⇩_{n}A = 0 ⟷ A ⊆ {0} ∧ finite A" by (induct A rule: infinite_finite_induct) simp_all lemma Lcm_fin_0_iff: "Lcm⇩_{f}⇩_{i}⇩_{n}A = 0 ⟷ 0 ∈ A" if "finite A" using that by (induct A) (auto simp: lcm_eq_0_iff) lemma Lcm_fin_1_iff: "Lcm⇩_{f}⇩_{i}⇩_{n}A = 1 ⟷ (∀a∈A. is_unit a) ∧ finite A" by (induct A rule: infinite_finite_induct) simp_all end context semiring_Gcd begin lemma Gcd_fin_eq_Gcd [simp]: "Gcd⇩_{f}⇩_{i}⇩_{n}A = Gcd A" if "finite A" for A :: "'a set" using that by induct simp_all lemma Gcd_set_eq_fold [code_unfold]: "Gcd (set xs) = fold gcd xs 0" by (simp add: Gcd_fin.set_eq_fold [symmetric]) lemma Lcm_fin_eq_Lcm [simp]: "Lcm⇩_{f}⇩_{i}⇩_{n}A = Lcm A" if "finite A" for A :: "'a set" using that by induct simp_all lemma Lcm_set_eq_fold [code_unfold]: "Lcm (set xs) = fold lcm xs 1" by (simp add: Lcm_fin.set_eq_fold [symmetric]) end subsection ‹Coprimality› context semiring_gcd begin lemma coprime_imp_gcd_eq_1 [simp]: "gcd a b = 1" if "coprime a b" proof - define t r s where "t = gcd a b" and "r = a div t" and "s = b div t" then have "a = t * r" and "b = t * s" by simp_all with that have "coprime (t * r) (t * s)" by simp then show ?thesis by (simp add: t_def) qed lemma gcd_eq_1_imp_coprime [dest!]: "coprime a b" if "gcd a b = 1" proof (rule coprimeI) fix c assume "c dvd a" and "c dvd b" then have "c dvd gcd a b" by (rule gcd_greatest) with that show "is_unit c" by simp qed lemma coprime_iff_gcd_eq_1 [presburger, code]: "coprime a b ⟷ gcd a b = 1" by rule (simp_all add: gcd_eq_1_imp_coprime) lemma is_unit_gcd [simp]: "is_unit (gcd a b) ⟷ coprime a b" by (simp add: coprime_iff_gcd_eq_1) lemma coprime_add_one_left [simp]: "coprime (a + 1) a" by (simp add: gcd_eq_1_imp_coprime ac_simps) lemma coprime_add_one_right [simp]: "coprime a (a + 1)" using coprime_add_one_left [of a] by (simp add: ac_simps) lemma coprime_mult_left_iff [simp]: "coprime (a * b) c ⟷ coprime a c ∧ coprime b c" proof assume "coprime (a * b) c" with coprime_common_divisor [of "a * b" c] have *: "is_unit d" if "d dvd a * b" and "d dvd c" for d using that by blast have "coprime a c" by (rule coprimeI, rule *) simp_all moreover have "coprime b c" by (rule coprimeI, rule *) simp_all ultimately show "coprime a c ∧ coprime b c" .. next assume "coprime a c ∧ coprime b c" then have "coprime a c" "coprime b c" by simp_all show "coprime (a * b) c" proof (rule coprimeI) fix d assume "d dvd a * b" then obtain r s where d: "d = r * s" "r dvd a" "s dvd b" by (rule dvd_productE) assume "d dvd c" with d have "r * s dvd c" by simp then have "r dvd c" "s dvd c" by (auto intro: dvd_mult_left dvd_mult_right) from ‹coprime a c› ‹r dvd a› ‹r dvd c› have "is_unit r" by (rule coprime_common_divisor) moreover from ‹coprime b c› ‹s dvd b› ‹s dvd c› have "is_unit s" by (rule coprime_common_divisor) ultimately show "is_unit d" by (simp add: d is_unit_mult_iff) qed qed lemma coprime_mult_right_iff [simp]: "coprime c (a * b) ⟷ coprime c a ∧ coprime c b" using coprime_mult_left_iff [of a b c] by (simp add: ac_simps) lemma coprime_power_left_iff [simp]: "coprime (a ^ n) b ⟷ coprime a b ∨ n = 0" proof (cases "n = 0") case True then show ?thesis by simp next case False then have "n > 0" by simp then show ?thesis by (induction n rule: nat_induct_non_zero) simp_all qed lemma coprime_power_right_iff [simp]: "coprime a (b ^ n) ⟷ coprime a b ∨ n = 0" using coprime_power_left_iff [of b n a] by (simp add: ac_simps) lemma prod_coprime_left: "coprime (∏i∈A. f i) a" if "⋀i. i ∈ A ⟹ coprime (f i) a" using that by (induct A rule: infinite_finite_induct) simp_all lemma prod_coprime_right: "coprime a (∏i∈A. f i)" if "⋀i. i ∈ A ⟹ coprime a (f i)" using that prod_coprime_left [of A f a] by (simp add: ac_simps) lemma prod_list_coprime_left: "coprime (prod_list xs) a" if "⋀x. x ∈ set xs ⟹ coprime x a" using that by (induct xs) simp_all lemma prod_list_coprime_right: "coprime a (prod_list xs)" if "⋀x. x ∈ set xs ⟹ coprime a x" using that prod_list_coprime_left [of xs a] by (simp add: ac_simps) lemma coprime_dvd_mult_left_iff: "a dvd b * c ⟷ a dvd b" if "coprime a c" proof assume "a dvd b" then show "a dvd b * c" by simp next assume "a dvd b * c" show "a dvd b" proof (cases "b = 0") case True then show ?thesis by simp next case False then have unit: "is_unit (unit_factor b)" by simp from ‹coprime a c› have "gcd (b * a) (b * c) * unit_factor b = b" by (subst gcd_mult_left) (simp add: ac_simps) moreover from ‹a dvd b * c› have "a dvd gcd (b * a) (b * c) * unit_factor b" by (simp add: dvd_mult_unit_iff unit) ultimately show ?thesis by simp qed qed lemma coprime_dvd_mult_right_iff: "a dvd c * b ⟷ a dvd b" if "coprime a c" using that coprime_dvd_mult_left_iff [of a c b] by (simp add: ac_simps) lemma divides_mult: "a * b dvd c" if "a dvd c" and "b dvd c" and "coprime a b" proof - from ‹b dvd c› obtain b' where "c = b * b'" .. with ‹a dvd c› have "a dvd b' * b" by (simp add: ac_simps) with ‹coprime a b› have "a dvd b'" by (simp add: coprime_dvd_mult_left_iff) then obtain a' where "b' = a * a'" .. with ‹c = b * b'› have "c = (a * b) * a'" by (simp add: ac_simps) then show ?thesis .. qed lemma div_gcd_coprime: assumes "a ≠ 0 ∨ b ≠ 0" shows "coprime (a div gcd a b) (b div gcd a b)" proof - let ?g = "gcd a b" let ?a' = "a div ?g" let ?b' = "b div ?g" let ?g' = "gcd ?a' ?b'" have dvdg: "?g dvd a" "?g dvd b" by simp_all have dvdg': "?g' dvd ?a'" "?g' dvd ?b'" by simp_all from dvdg dvdg' obtain ka kb ka' kb' where kab: "a = ?g * ka" "b = ?g * kb" "?a' = ?g' * ka'" "?b' = ?g' * kb'" unfolding dvd_def by blast from this [symmetric] have "?g * ?a' = (?g * ?g') * ka'" "?g * ?b' = (?g * ?g') * kb'" by (simp_all add: mult.assoc mult.left_commute [of "gcd a b"]) then have dvdgg':"?g * ?g' dvd a" "?g* ?g' dvd b" by (auto simp: dvd_mult_div_cancel [OF dvdg(1)] dvd_mult_div_cancel [OF dvdg(2)] dvd_def) have "?g ≠ 0" using assms by simp moreover from gcd_greatest [OF dvdgg'] have "?g * ?g' dvd ?g" . ultimately show ?thesis using dvd_times_left_cancel_iff [of "gcd a b" _ 1] by simp (simp only: coprime_iff_gcd_eq_1) qed lemma gcd_coprime: assumes c: "gcd a b ≠ 0" and a: "a = a' * gcd a b" and b: "b = b' * gcd a b" shows "coprime a' b'" proof - from c have "a ≠ 0 ∨ b ≠ 0" by simp with div_gcd_coprime have "coprime (a div gcd a b) (b div gcd a b)" . also from assms have "a div gcd a b = a'" using dvd_div_eq_mult gcd_dvd1 by blast also from assms have "b div gcd a b = b'" using dvd_div_eq_mult gcd_dvd1 by blast finally show ?thesis . qed lemma gcd_coprime_exists: assumes "gcd a b ≠ 0" shows "∃a' b'. a = a' * gcd a b ∧ b = b' * gcd a b ∧ coprime a' b'" proof - have "coprime (a div gcd a b) (b div gcd a b)" using assms div_gcd_coprime by auto then show ?thesis by force qed lemma pow_divides_pow_iff [simp]: "a ^ n dvd b ^ n ⟷ a dvd b" if "n > 0" proof (cases "gcd a b = 0") case True then show ?thesis by simp next case False show ?thesis proof let ?d = "gcd a b" from ‹n > 0› obtain m where m: "n = Suc m" by (cases n) simp_all from False have zn: "?d ^ n ≠ 0" by (rule power_not_zero) from gcd_coprime_exists [OF False] obtain a' b' where ab': "a = a' * ?d" "b = b' * ?d" "coprime a' b'" by blast assume "a ^ n dvd b ^ n" then have "(a' * ?d) ^ n dvd (b' * ?d) ^ n" by (simp add: ab'(1,2)[symmetric]) then have "?d^n * a'^n dvd ?d^n * b'^n" by (simp only: power_mult_distrib ac_simps) with zn have "a' ^ n dvd b' ^ n" by simp then have "a' dvd b' ^ n" using dvd_trans[of a' "a'^n" "b'^n"] by (simp add: m) then have "a' dvd b' ^ m * b'" by (simp add: m ac_simps) moreover have "coprime a' (b' ^ n)" using ‹coprime a' b'› by simp then have "a' dvd b'" using ‹a' dvd b' ^ n› coprime_dvd_mult_left_iff dvd_mult by blast then have "a' * ?d dvd b' * ?d" by (rule mult_dvd_mono) simp with ab'(1,2) show "a dvd b" by simp next assume "a dvd b" with ‹n > 0› show "a ^ n dvd b ^ n" by (induction rule: nat_induct_non_zero) (simp_all add: mult_dvd_mono) qed qed lemma coprime_crossproduct: fixes a b c d :: 'a assumes "coprime a d" and "coprime b c" shows "normalize a * normalize c = normalize b * normalize d ⟷ normalize a = normalize b ∧ normalize c = normalize d" (is "?lhs ⟷ ?rhs") proof assume ?rhs then show ?lhs by simp next assume ?lhs from ‹?lhs› have "normalize a dvd normalize b * normalize d" by (auto intro: dvdI dest: sym) with ‹coprime a d› have "a dvd b" by (simp add: coprime_dvd_mult_left_iff normalize_mult [symmetric]) from ‹?lhs› have "normalize b dvd normalize a * normalize c" by (auto intro: dvdI dest: sym) with ‹coprime b c› have "b dvd a" by (simp add: coprime_dvd_mult_left_iff normalize_mult [symmetric]) from ‹?lhs› have "normalize c dvd normalize d * normalize b" by (auto intro: dvdI dest: sym simp add: mult.commute) with ‹coprime b c› have "c dvd d" by (simp add: coprime_dvd_mult_left_iff coprime_commute normalize_mult [symmetric]) from ‹?lhs› have "normalize d dvd normalize c * normalize a" by (auto intro: dvdI dest: sym simp add: mult.commute) with ‹coprime a d› have "d dvd c" by (simp add: coprime_dvd_mult_left_iff coprime_commute normalize_mult [symmetric]) from ‹a dvd b› ‹b dvd a› have "normalize a = normalize b" by (rule associatedI) moreover from ‹c dvd d› ‹d dvd c› have "normalize c = normalize d" by (rule associatedI) ultimately show ?rhs .. qed lemma gcd_mult_left_left_cancel: "gcd (c * a) b = gcd a b" if "coprime b c" proof - have "coprime (gcd b (a * c)) c" by (rule coprimeI) (auto intro: that coprime_common_divisor) then have "gcd b (a * c) dvd a" using coprime_dvd_mult_left_iff [of "gcd b (a * c)" c a] by simp then show ?thesis by (auto intro: associated_eqI simp add: ac_simps) qed lemma gcd_mult_left_right_cancel: "gcd (a * c) b = gcd a b" if "coprime b c" using that gcd_mult_left_left_cancel [of b c a] by (simp add: ac_simps) lemma gcd_mult_right_left_cancel: "gcd a (c * b) = gcd a b" if "coprime a c" using that gcd_mult_left_left_cancel [of a c b] by (simp add: ac_simps) lemma gcd_mult_right_right_cancel: "gcd a (b * c) = gcd a b" if "coprime a c" using that gcd_mult_right_left_cancel [of a c b] by (simp add: ac_simps) lemma gcd_exp_weak: "gcd (a ^ n) (b ^ n) = normalize (gcd a b ^ n)" proof (cases "a = 0 ∧ b = 0 ∨ n = 0") case True then show ?thesis by (cases n) simp_all next case False then have "coprime (a div gcd a b) (b div gcd a b)" and "n > 0" by (auto intro: div_gcd_coprime) then have "coprime ((a div gcd a b) ^ n) ((b div gcd a b) ^ n)" by simp then have "1 = gcd ((a div gcd a b) ^ n) ((b div gcd a b) ^ n)" by simp then have "normalize (gcd a b ^ n) = normalize (gcd a b ^ n * …)" by simp also have "… = gcd (gcd a b ^ n * (a div gcd a b) ^ n) (gcd a b ^ n * (b div gcd a b) ^ n)" by (rule gcd_mult_left [symmetric]) also have "(gcd a b) ^ n * (a div gcd a b) ^ n = a ^ n" by (simp add: ac_simps div_power dvd_power_same) also have "(gcd a b) ^ n * (b div gcd a b) ^ n = b ^ n" by (simp add: ac_simps div_power dvd_power_same) finally show ?thesis by simp qed lemma division_decomp: assumes "a dvd b * c" shows "∃b' c'. a = b' * c' ∧ b' dvd b ∧ c' dvd c" proof (cases "gcd a b = 0") case True then have "a = 0 ∧ b = 0" by simp then have "a = 0 * c ∧ 0 dvd b ∧ c dvd c" by simp then show ?thesis by blast next case False let ?d = "gcd a b" from gcd_coprime_exists [OF False] obtain a' b' where ab': "a = a' * ?d" "b = b' * ?d" "coprime a' b'" by blast from ab'(1) have "a' dvd a" .. with assms have "a' dvd b * c" using dvd_trans [of a' a "b * c"] by simp from assms ab'(1,2) have "a' * ?d dvd (b' * ?d) * c" by simp then have "?d * a' dvd ?d * (b' * c)" by (simp add: mult_ac) with ‹?d ≠ 0› have "a' dvd b' * c" by simp then have "a' dvd c" using ‹coprime a' b'› by (simp add: coprime_dvd_mult_right_iff) with ab'(1) have "a = ?d * a' ∧ ?d dvd b ∧ a' dvd c" by (simp add: ac_simps) then show ?thesis by blast qed lemma lcm_coprime: "coprime a b ⟹ lcm a b = normalize (a * b)" by (subst lcm_gcd) simp end context ring_gcd begin lemma coprime_minus_left_iff [simp]: "coprime (- a) b ⟷ coprime a b" by (rule; rule coprimeI) (auto intro: coprime_common_divisor) lemma coprime_minus_right_iff [simp]: "coprime a (- b) ⟷ coprime a b" using coprime_minus_left_iff [of b a] by (simp add: ac_simps) lemma coprime_diff_one_left [simp]: "coprime (a - 1) a" using coprime_add_one_right [of "a - 1"] by simp lemma coprime_doff_one_right [simp]: "coprime a (a - 1)" using coprime_diff_one_left [of a] by (simp add: ac_simps) end context semiring_Gcd begin lemma Lcm_coprime: assumes "finite A" and "A ≠ {}" and "⋀a b. a ∈ A ⟹ b ∈ A ⟹ a ≠ b ⟹ coprime a b" shows "Lcm A = normalize (∏A)" using assms proof (induct rule: finite_ne_induct) case singleton then show ?case by simp next case (insert a A) have "Lcm (insert a A) = lcm a (Lcm A)" by simp also from insert have "Lcm A = normalize (∏A)" by blast also have "lcm a … = lcm a (∏A)" by (cases "∏A = 0") (simp_all add: lcm_div_unit2) also from insert have "coprime a (∏A)" by (subst coprime_commute, intro prod_coprime_left) auto with insert have "lcm a (∏A) = normalize (∏(insert a A))" by (simp add: lcm_coprime) finally show ?case . qed lemma Lcm_coprime': "card A ≠ 0 ⟹ (⋀a b. a ∈ A ⟹ b ∈ A ⟹ a ≠ b ⟹ coprime a b) ⟹ Lcm A = normalize (∏A)" by (rule Lcm_coprime) (simp_all add: card_eq_0_iff) end text ‹And some consequences: cancellation modulo @{term m}› lemma mult_mod_cancel_right: fixes m :: "'a::{euclidean_ring_cancel,semiring_gcd}" assumes eq: "(a * n) mod m = (b * n) mod m" and "coprime m n" shows "a mod m = b mod m" proof - have "m dvd (a*n - b*n)" using eq mod_eq_dvd_iff by blast then have "m dvd a-b" by (metis ‹coprime m n› coprime_dvd_mult_left_iff left_diff_distrib') then show ?thesis using mod_eq_dvd_iff by blast qed lemma mult_mod_cancel_left: fixes m :: "'a::{euclidean_ring_cancel,semiring_gcd}" assumes "(n * a) mod m = (n * b) mod m" and "coprime m n" shows "a mod m = b mod m" by (metis assms mult.commute mult_mod_cancel_right) subsection ‹GCD and LCM for multiplicative normalisation functions› class semiring_gcd_mult_normalize = semiring_gcd + normalization_semidom_multiplicative begin lemma mult_gcd_left: "c * gcd a b = unit_factor c * gcd (c * a) (c * b)" by (simp add: gcd_mult_left normalize_mult mult.assoc [symmetric]) lemma mult_gcd_right: "gcd a b * c = gcd (a * c) (b * c) * unit_factor c" using mult_gcd_left [of c a b] by (simp add: ac_simps) lemma gcd_mult_distrib': "normalize c * gcd a b = gcd (c * a) (c * b)" by (subst gcd_mult_left) (simp_all add: normalize_mult) lemma gcd_mult_distrib: "k * gcd a b = gcd (k * a) (k * b) * unit_factor k" proof- have "normalize k * gcd a b = gcd (k * a) (k * b)" by (simp add: gcd_mult_distrib') then have "normalize k * gcd a b * unit_factor k = gcd (k * a) (k * b) * unit_factor k" by simp then have "normalize k * unit_factor k * gcd a b = gcd (k * a) (k * b) * unit_factor k" by (simp only: ac_simps) then show ?thesis by simp qed lemma gcd_mult_lcm [simp]: "gcd a b * lcm a b = normalize a * normalize b" by (simp add: lcm_gcd normalize_mult dvd_normalize_div) lemma lcm_mult_gcd [simp]: "lcm a b * gcd a b = normalize a * normalize b" using gcd_mult_lcm [of a b] by (simp add: ac_simps) lemma mult_lcm_left: "c * lcm a b = unit_factor c * lcm (c * a) (c * b)" by (simp add: lcm_mult_left mult.assoc [symmetric] normalize_mult) lemma mult_lcm_right: "lcm a b * c = lcm (a * c) (b * c) * unit_factor c" using mult_lcm_left [of c a b] by (simp add: ac_simps) lemma lcm_gcd_prod: "lcm a b * gcd a b = normalize (a * b)" by (simp add: lcm_gcd dvd_normalize_div normalize_mult) lemma lcm_mult_distrib': "normalize c * lcm a b = lcm (c * a) (c * b)" by (subst lcm_mult_left) (simp add: normalize_mult) lemma lcm_mult_distrib: "k * lcm a b = lcm (k * a) (k * b) * unit_factor k" proof- have "normalize k * lcm a b = lcm (k * a) (k * b)" by (simp add: lcm_mult_distrib') then have "normalize k * lcm a b * unit_factor k = lcm (k * a) (k * b) * unit_factor k" by simp then have "normalize k * unit_factor k * lcm a b = lcm (k * a) (k * b)</