author | haftmann |
Sat, 11 Nov 2017 18:41:08 +0000 | |
changeset 67051 | e7e54a0b9197 |
parent 66840 | 0d689d71dbdc |
child 67083 | 6b2c0681ef28 |
permissions | -rw-r--r-- |
41959 | 1 |
(* Title: HOL/Parity.thy |
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Author: Jeremy Avigad |
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Author: Jacques D. Fleuriot |
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*) |
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section \<open>Parity in rings and semirings\<close> |
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theory Parity |
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imports Euclidean_Division |
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begin |
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subsection \<open>Ring structures with parity and \<open>even\<close>/\<open>odd\<close> predicates\<close> |
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class semiring_parity = linordered_semidom + unique_euclidean_semiring + |
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assumes of_nat_div: "of_nat (m div n) = of_nat m div of_nat n" |
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and division_segment_of_nat [simp]: "division_segment (of_nat n) = 1" |
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and division_segment_euclidean_size [simp]: "division_segment a * of_nat (euclidean_size a) = a" |
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begin |
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lemma division_segment_eq_iff: |
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"a = b" if "division_segment a = division_segment b" |
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and "euclidean_size a = euclidean_size b" |
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using that division_segment_euclidean_size [of a] by simp |
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lemma euclidean_size_of_nat [simp]: |
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"euclidean_size (of_nat n) = n" |
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proof - |
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have "division_segment (of_nat n) * of_nat (euclidean_size (of_nat n)) = of_nat n" |
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by (fact division_segment_euclidean_size) |
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then show ?thesis by simp |
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qed |
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lemma of_nat_euclidean_size: |
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"of_nat (euclidean_size a) = a div division_segment a" |
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proof - |
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have "of_nat (euclidean_size a) = division_segment a * of_nat (euclidean_size a) div division_segment a" |
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by (subst nonzero_mult_div_cancel_left) simp_all |
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also have "\<dots> = a div division_segment a" |
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by simp |
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finally show ?thesis . |
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qed |
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||
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lemma division_segment_1 [simp]: |
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"division_segment 1 = 1" |
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using division_segment_of_nat [of 1] by simp |
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||
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lemma division_segment_numeral [simp]: |
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"division_segment (numeral k) = 1" |
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using division_segment_of_nat [of "numeral k"] by simp |
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||
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lemma euclidean_size_1 [simp]: |
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"euclidean_size 1 = 1" |
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using euclidean_size_of_nat [of 1] by simp |
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||
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lemma euclidean_size_numeral [simp]: |
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"euclidean_size (numeral k) = numeral k" |
|
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using euclidean_size_of_nat [of "numeral k"] by simp |
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lemma of_nat_dvd_iff: |
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"of_nat m dvd of_nat n \<longleftrightarrow> m dvd n" (is "?P \<longleftrightarrow> ?Q") |
|
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proof (cases "m = 0") |
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case True |
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then show ?thesis |
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by simp |
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next |
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case False |
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show ?thesis |
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proof |
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assume ?Q |
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then show ?P |
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by (auto elim: dvd_class.dvdE) |
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next |
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assume ?P |
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with False have "of_nat n = of_nat n div of_nat m * of_nat m" |
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by simp |
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then have "of_nat n = of_nat (n div m * m)" |
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by (simp add: of_nat_div) |
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then have "n = n div m * m" |
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by (simp only: of_nat_eq_iff) |
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then have "n = m * (n div m)" |
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by (simp add: ac_simps) |
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then show ?Q .. |
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qed |
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qed |
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||
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lemma of_nat_mod: |
|
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"of_nat (m mod n) = of_nat m mod of_nat n" |
|
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proof - |
|
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have "of_nat m div of_nat n * of_nat n + of_nat m mod of_nat n = of_nat m" |
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by (simp add: div_mult_mod_eq) |
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also have "of_nat m = of_nat (m div n * n + m mod n)" |
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by simp |
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finally show ?thesis |
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by (simp only: of_nat_div of_nat_mult of_nat_add) simp |
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qed |
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lemma one_div_two_eq_zero [simp]: |
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"1 div 2 = 0" |
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proof - |
|
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from of_nat_div [symmetric] have "of_nat 1 div of_nat 2 = of_nat 0" |
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by (simp only:) simp |
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then show ?thesis |
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by simp |
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qed |
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lemma one_mod_two_eq_one [simp]: |
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"1 mod 2 = 1" |
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proof - |
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from of_nat_mod [symmetric] have "of_nat 1 mod of_nat 2 = of_nat 1" |
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by (simp only:) simp |
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then show ?thesis |
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by simp |
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qed |
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abbreviation even :: "'a \<Rightarrow> bool" |
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where "even a \<equiv> 2 dvd a" |
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abbreviation odd :: "'a \<Rightarrow> bool" |
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where "odd a \<equiv> \<not> 2 dvd a" |
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lemma even_iff_mod_2_eq_zero: |
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"even a \<longleftrightarrow> a mod 2 = 0" |
|
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by (fact dvd_eq_mod_eq_0) |
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lemma odd_iff_mod_2_eq_one: |
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"odd a \<longleftrightarrow> a mod 2 = 1" |
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proof |
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assume "a mod 2 = 1" |
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then show "odd a" |
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by auto |
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next |
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assume "odd a" |
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have eucl: "euclidean_size (a mod 2) = 1" |
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proof (rule order_antisym) |
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show "euclidean_size (a mod 2) \<le> 1" |
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using mod_size_less [of 2 a] by simp |
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show "1 \<le> euclidean_size (a mod 2)" |
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using \<open>odd a\<close> by (simp add: Suc_le_eq dvd_eq_mod_eq_0) |
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qed |
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from \<open>odd a\<close> have "\<not> of_nat 2 dvd division_segment a * of_nat (euclidean_size a)" |
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by simp |
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then have "\<not> of_nat 2 dvd of_nat (euclidean_size a)" |
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by (auto simp only: dvd_mult_unit_iff' is_unit_division_segment) |
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then have "\<not> 2 dvd euclidean_size a" |
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using of_nat_dvd_iff [of 2] by simp |
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then have "euclidean_size a mod 2 = 1" |
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by (simp add: semidom_modulo_class.dvd_eq_mod_eq_0) |
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then have "of_nat (euclidean_size a mod 2) = of_nat 1" |
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by simp |
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then have "of_nat (euclidean_size a) mod 2 = 1" |
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by (simp add: of_nat_mod) |
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from \<open>odd a\<close> eucl |
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show "a mod 2 = 1" |
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by (auto intro: division_segment_eq_iff simp add: division_segment_mod) |
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qed |
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lemma parity_cases [case_names even odd]: |
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assumes "even a \<Longrightarrow> a mod 2 = 0 \<Longrightarrow> P" |
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assumes "odd a \<Longrightarrow> a mod 2 = 1 \<Longrightarrow> P" |
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shows P |
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using assms by (cases "even a") (simp_all add: odd_iff_mod_2_eq_one) |
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lemma not_mod_2_eq_1_eq_0 [simp]: |
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"a mod 2 \<noteq> 1 \<longleftrightarrow> a mod 2 = 0" |
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by (cases a rule: parity_cases) simp_all |
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lemma not_mod_2_eq_0_eq_1 [simp]: |
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"a mod 2 \<noteq> 0 \<longleftrightarrow> a mod 2 = 1" |
|
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by (cases a rule: parity_cases) simp_all |
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lemma evenE [elim?]: |
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assumes "even a" |
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obtains b where "a = 2 * b" |
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using assms by (rule dvdE) |
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lemma oddE [elim?]: |
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assumes "odd a" |
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obtains b where "a = 2 * b + 1" |
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proof - |
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have "a = 2 * (a div 2) + a mod 2" |
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by (simp add: mult_div_mod_eq) |
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with assms have "a = 2 * (a div 2) + 1" |
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by (simp add: odd_iff_mod_2_eq_one) |
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then show ?thesis .. |
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qed |
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lemma mod_2_eq_odd: |
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"a mod 2 = of_bool (odd a)" |
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by (auto elim: oddE) |
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lemma one_mod_2_pow_eq [simp]: |
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"1 mod (2 ^ n) = of_bool (n > 0)" |
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proof - |
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have "1 mod (2 ^ n) = (of_bool (n > 0) :: nat)" |
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by (induct n) (simp_all add: mod_mult2_eq) |
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then have "of_nat (1 mod (2 ^ n)) = of_bool (n > 0)" |
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by simp |
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then show ?thesis |
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by (simp add: of_nat_mod) |
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qed |
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lemma even_of_nat [simp]: |
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"even (of_nat a) \<longleftrightarrow> even a" |
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proof - |
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have "even (of_nat a) \<longleftrightarrow> of_nat 2 dvd of_nat a" |
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by simp |
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also have "\<dots> \<longleftrightarrow> even a" |
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by (simp only: of_nat_dvd_iff) |
|
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finally show ?thesis . |
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qed |
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lemma even_zero [simp]: |
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"even 0" |
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by (fact dvd_0_right) |
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lemma odd_one [simp]: |
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"odd 1" |
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proof - |
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have "\<not> (2 :: nat) dvd 1" |
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by simp |
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then have "\<not> of_nat 2 dvd of_nat 1" |
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unfolding of_nat_dvd_iff by simp |
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then show ?thesis |
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by simp |
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qed |
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lemma odd_even_add: |
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"even (a + b)" if "odd a" and "odd b" |
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proof - |
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from that obtain c d where "a = 2 * c + 1" and "b = 2 * d + 1" |
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by (blast elim: oddE) |
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then have "a + b = 2 * c + 2 * d + (1 + 1)" |
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by (simp only: ac_simps) |
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also have "\<dots> = 2 * (c + d + 1)" |
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by (simp add: algebra_simps) |
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finally show ?thesis .. |
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qed |
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lemma even_add [simp]: |
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"even (a + b) \<longleftrightarrow> (even a \<longleftrightarrow> even b)" |
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by (auto simp add: dvd_add_right_iff dvd_add_left_iff odd_even_add) |
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lemma odd_add [simp]: |
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"odd (a + b) \<longleftrightarrow> \<not> (odd a \<longleftrightarrow> odd b)" |
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by simp |
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lemma even_plus_one_iff [simp]: |
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"even (a + 1) \<longleftrightarrow> odd a" |
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by (auto simp add: dvd_add_right_iff intro: odd_even_add) |
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lemma even_mult_iff [simp]: |
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"even (a * b) \<longleftrightarrow> even a \<or> even b" (is "?P \<longleftrightarrow> ?Q") |
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proof |
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assume ?Q |
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then show ?P |
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by auto |
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next |
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assume ?P |
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show ?Q |
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proof (rule ccontr) |
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assume "\<not> (even a \<or> even b)" |
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then have "odd a" and "odd b" |
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by auto |
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then obtain r s where "a = 2 * r + 1" and "b = 2 * s + 1" |
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by (blast elim: oddE) |
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then have "a * b = (2 * r + 1) * (2 * s + 1)" |
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by simp |
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also have "\<dots> = 2 * (2 * r * s + r + s) + 1" |
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by (simp add: algebra_simps) |
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finally have "odd (a * b)" |
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by simp |
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with \<open>?P\<close> show False |
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by auto |
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qed |
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qed |
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lemma even_numeral [simp]: "even (numeral (Num.Bit0 n))" |
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proof - |
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have "even (2 * numeral n)" |
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unfolding even_mult_iff by simp |
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then have "even (numeral n + numeral n)" |
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unfolding mult_2 . |
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then show ?thesis |
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unfolding numeral.simps . |
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qed |
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lemma odd_numeral [simp]: "odd (numeral (Num.Bit1 n))" |
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proof |
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assume "even (numeral (num.Bit1 n))" |
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then have "even (numeral n + numeral n + 1)" |
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unfolding numeral.simps . |
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then have "even (2 * numeral n + 1)" |
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unfolding mult_2 . |
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294 |
then have "2 dvd numeral n * 2 + 1" |
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by (simp add: ac_simps) |
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then have "2 dvd 1" |
297 |
using dvd_add_times_triv_left_iff [of 2 "numeral n" 1] by simp |
|
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then show False by simp |
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qed |
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300 |
|
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lemma even_power [simp]: "even (a ^ n) \<longleftrightarrow> even a \<and> n > 0" |
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by (induct n) auto |
303 |
||
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lemma even_succ_div_two [simp]: |
305 |
"even a \<Longrightarrow> (a + 1) div 2 = a div 2" |
|
306 |
by (cases "a = 0") (auto elim!: evenE dest: mult_not_zero) |
|
307 |
||
308 |
lemma odd_succ_div_two [simp]: |
|
309 |
"odd a \<Longrightarrow> (a + 1) div 2 = a div 2 + 1" |
|
310 |
by (auto elim!: oddE simp add: add.assoc) |
|
311 |
||
312 |
lemma even_two_times_div_two: |
|
313 |
"even a \<Longrightarrow> 2 * (a div 2) = a" |
|
314 |
by (fact dvd_mult_div_cancel) |
|
315 |
||
316 |
lemma odd_two_times_div_two_succ [simp]: |
|
317 |
"odd a \<Longrightarrow> 2 * (a div 2) + 1 = a" |
|
318 |
using mult_div_mod_eq [of 2 a] |
|
319 |
by (simp add: even_iff_mod_2_eq_zero) |
|
320 |
||
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lemma coprime_left_2_iff_odd [simp]: |
322 |
"coprime 2 a \<longleftrightarrow> odd a" |
|
323 |
proof |
|
324 |
assume "odd a" |
|
325 |
show "coprime 2 a" |
|
326 |
proof (rule coprimeI) |
|
327 |
fix b |
|
328 |
assume "b dvd 2" "b dvd a" |
|
329 |
then have "b dvd a mod 2" |
|
330 |
by (auto intro: dvd_mod) |
|
331 |
with \<open>odd a\<close> show "is_unit b" |
|
332 |
by (simp add: mod_2_eq_odd) |
|
333 |
qed |
|
334 |
next |
|
335 |
assume "coprime 2 a" |
|
336 |
show "odd a" |
|
337 |
proof (rule notI) |
|
338 |
assume "even a" |
|
339 |
then obtain b where "a = 2 * b" .. |
|
340 |
with \<open>coprime 2 a\<close> have "coprime 2 (2 * b)" |
|
341 |
by simp |
|
342 |
moreover have "\<not> coprime 2 (2 * b)" |
|
343 |
by (rule not_coprimeI [of 2]) simp_all |
|
344 |
ultimately show False |
|
345 |
by blast |
|
346 |
qed |
|
347 |
qed |
|
348 |
||
349 |
lemma coprime_right_2_iff_odd [simp]: |
|
350 |
"coprime a 2 \<longleftrightarrow> odd a" |
|
351 |
using coprime_left_2_iff_odd [of a] by (simp add: ac_simps) |
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end |
398e05aa84d4
purely algebraic characterization of even and odd
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|
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034b13f4efae
distributivity of partial minus establishes desired properties of dvd in semirings
haftmann
parents:
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diff
changeset
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355 |
class ring_parity = ring + semiring_parity |
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begin |
357 |
||
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358 |
subclass comm_ring_1 .. |
034b13f4efae
distributivity of partial minus establishes desired properties of dvd in semirings
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diff
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|
359 |
|
66815 | 360 |
lemma even_minus [simp]: |
361 |
"even (- a) \<longleftrightarrow> even a" |
|
58740 | 362 |
by (fact dvd_minus_iff) |
58679 | 363 |
|
66815 | 364 |
lemma even_diff [simp]: |
365 |
"even (a - b) \<longleftrightarrow> even (a + b)" |
|
58680 | 366 |
using even_add [of a "- b"] by simp |
367 |
||
58679 | 368 |
end |
369 |
||
66808
1907167b6038
elementary definition of division on natural numbers
haftmann
parents:
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|
370 |
|
66815 | 371 |
subsection \<open>Instance for @{typ nat}\<close> |
66808
1907167b6038
elementary definition of division on natural numbers
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parents:
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changeset
|
372 |
|
66815 | 373 |
instance nat :: semiring_parity |
374 |
by standard (simp_all add: dvd_eq_mod_eq_0) |
|
66808
1907167b6038
elementary definition of division on natural numbers
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parents:
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diff
changeset
|
375 |
|
66815 | 376 |
lemma even_Suc_Suc_iff [simp]: |
377 |
"even (Suc (Suc n)) \<longleftrightarrow> even n" |
|
58787 | 378 |
using dvd_add_triv_right_iff [of 2 n] by simp |
58687 | 379 |
|
66815 | 380 |
lemma even_Suc [simp]: "even (Suc n) \<longleftrightarrow> odd n" |
381 |
using even_plus_one_iff [of n] by simp |
|
58787 | 382 |
|
66815 | 383 |
lemma even_diff_nat [simp]: |
384 |
"even (m - n) \<longleftrightarrow> m < n \<or> even (m + n)" for m n :: nat |
|
58787 | 385 |
proof (cases "n \<le> m") |
386 |
case True |
|
387 |
then have "m - n + n * 2 = m + n" by (simp add: mult_2_right) |
|
66815 | 388 |
moreover have "even (m - n) \<longleftrightarrow> even (m - n + n * 2)" by simp |
389 |
ultimately have "even (m - n) \<longleftrightarrow> even (m + n)" by (simp only:) |
|
58787 | 390 |
then show ?thesis by auto |
391 |
next |
|
392 |
case False |
|
393 |
then show ?thesis by simp |
|
63654 | 394 |
qed |
395 |
||
66815 | 396 |
lemma odd_pos: |
397 |
"odd n \<Longrightarrow> 0 < n" for n :: nat |
|
58690 | 398 |
by (auto elim: oddE) |
60343
063698416239
correct sort constraints for abbreviations in type classes
haftmann
parents:
59816
diff
changeset
|
399 |
|
66815 | 400 |
lemma Suc_double_not_eq_double: |
401 |
"Suc (2 * m) \<noteq> 2 * n" |
|
62597 | 402 |
proof |
403 |
assume "Suc (2 * m) = 2 * n" |
|
404 |
moreover have "odd (Suc (2 * m))" and "even (2 * n)" |
|
405 |
by simp_all |
|
406 |
ultimately show False by simp |
|
407 |
qed |
|
408 |
||
66815 | 409 |
lemma double_not_eq_Suc_double: |
410 |
"2 * m \<noteq> Suc (2 * n)" |
|
62597 | 411 |
using Suc_double_not_eq_double [of n m] by simp |
412 |
||
66815 | 413 |
lemma odd_Suc_minus_one [simp]: "odd n \<Longrightarrow> Suc (n - Suc 0) = n" |
414 |
by (auto elim: oddE) |
|
60343
063698416239
correct sort constraints for abbreviations in type classes
haftmann
parents:
59816
diff
changeset
|
415 |
|
66815 | 416 |
lemma even_Suc_div_two [simp]: |
417 |
"even n \<Longrightarrow> Suc n div 2 = n div 2" |
|
418 |
using even_succ_div_two [of n] by simp |
|
60343
063698416239
correct sort constraints for abbreviations in type classes
haftmann
parents:
59816
diff
changeset
|
419 |
|
66815 | 420 |
lemma odd_Suc_div_two [simp]: |
421 |
"odd n \<Longrightarrow> Suc n div 2 = Suc (n div 2)" |
|
422 |
using odd_succ_div_two [of n] by simp |
|
60343
063698416239
correct sort constraints for abbreviations in type classes
haftmann
parents:
59816
diff
changeset
|
423 |
|
66815 | 424 |
lemma odd_two_times_div_two_nat [simp]: |
425 |
assumes "odd n" |
|
426 |
shows "2 * (n div 2) = n - (1 :: nat)" |
|
427 |
proof - |
|
428 |
from assms have "2 * (n div 2) + 1 = n" |
|
429 |
by (rule odd_two_times_div_two_succ) |
|
430 |
then have "Suc (2 * (n div 2)) - 1 = n - 1" |
|
58787 | 431 |
by simp |
66815 | 432 |
then show ?thesis |
433 |
by simp |
|
58787 | 434 |
qed |
58680 | 435 |
|
66815 | 436 |
lemma parity_induct [case_names zero even odd]: |
437 |
assumes zero: "P 0" |
|
438 |
assumes even: "\<And>n. P n \<Longrightarrow> P (2 * n)" |
|
439 |
assumes odd: "\<And>n. P n \<Longrightarrow> P (Suc (2 * n))" |
|
440 |
shows "P n" |
|
441 |
proof (induct n rule: less_induct) |
|
442 |
case (less n) |
|
443 |
show "P n" |
|
444 |
proof (cases "n = 0") |
|
445 |
case True with zero show ?thesis by simp |
|
446 |
next |
|
447 |
case False |
|
448 |
with less have hyp: "P (n div 2)" by simp |
|
449 |
show ?thesis |
|
450 |
proof (cases "even n") |
|
451 |
case True |
|
452 |
with hyp even [of "n div 2"] show ?thesis |
|
453 |
by simp |
|
454 |
next |
|
455 |
case False |
|
456 |
with hyp odd [of "n div 2"] show ?thesis |
|
457 |
by simp |
|
458 |
qed |
|
459 |
qed |
|
460 |
qed |
|
58687 | 461 |
|
462 |
||
60758 | 463 |
subsection \<open>Parity and powers\<close> |
58689 | 464 |
|
61531
ab2e862263e7
Rounding function, uniform limits, cotangent, binomial identities
eberlm
parents:
60867
diff
changeset
|
465 |
context ring_1 |
58689 | 466 |
begin |
467 |
||
63654 | 468 |
lemma power_minus_even [simp]: "even n \<Longrightarrow> (- a) ^ n = a ^ n" |
58690 | 469 |
by (auto elim: evenE) |
58689 | 470 |
|
63654 | 471 |
lemma power_minus_odd [simp]: "odd n \<Longrightarrow> (- a) ^ n = - (a ^ n)" |
58690 | 472 |
by (auto elim: oddE) |
473 |
||
66815 | 474 |
lemma uminus_power_if: |
475 |
"(- a) ^ n = (if even n then a ^ n else - (a ^ n))" |
|
476 |
by auto |
|
477 |
||
63654 | 478 |
lemma neg_one_even_power [simp]: "even n \<Longrightarrow> (- 1) ^ n = 1" |
58690 | 479 |
by simp |
58689 | 480 |
|
63654 | 481 |
lemma neg_one_odd_power [simp]: "odd n \<Longrightarrow> (- 1) ^ n = - 1" |
58690 | 482 |
by simp |
58689 | 483 |
|
66582 | 484 |
lemma neg_one_power_add_eq_neg_one_power_diff: "k \<le> n \<Longrightarrow> (- 1) ^ (n + k) = (- 1) ^ (n - k)" |
485 |
by (cases "even (n + k)") auto |
|
486 |
||
63654 | 487 |
end |
58689 | 488 |
|
489 |
context linordered_idom |
|
490 |
begin |
|
491 |
||
63654 | 492 |
lemma zero_le_even_power: "even n \<Longrightarrow> 0 \<le> a ^ n" |
58690 | 493 |
by (auto elim: evenE) |
58689 | 494 |
|
63654 | 495 |
lemma zero_le_odd_power: "odd n \<Longrightarrow> 0 \<le> a ^ n \<longleftrightarrow> 0 \<le> a" |
58689 | 496 |
by (auto simp add: power_even_eq zero_le_mult_iff elim: oddE) |
497 |
||
63654 | 498 |
lemma zero_le_power_eq: "0 \<le> a ^ n \<longleftrightarrow> even n \<or> odd n \<and> 0 \<le> a" |
58787 | 499 |
by (auto simp add: zero_le_even_power zero_le_odd_power) |
63654 | 500 |
|
501 |
lemma zero_less_power_eq: "0 < a ^ n \<longleftrightarrow> n = 0 \<or> even n \<and> a \<noteq> 0 \<or> odd n \<and> 0 < a" |
|
58689 | 502 |
proof - |
503 |
have [simp]: "0 = a ^ n \<longleftrightarrow> a = 0 \<and> n > 0" |
|
58787 | 504 |
unfolding power_eq_0_iff [of a n, symmetric] by blast |
58689 | 505 |
show ?thesis |
63654 | 506 |
unfolding less_le zero_le_power_eq by auto |
58689 | 507 |
qed |
508 |
||
63654 | 509 |
lemma power_less_zero_eq [simp]: "a ^ n < 0 \<longleftrightarrow> odd n \<and> a < 0" |
58689 | 510 |
unfolding not_le [symmetric] zero_le_power_eq by auto |
511 |
||
63654 | 512 |
lemma power_le_zero_eq: "a ^ n \<le> 0 \<longleftrightarrow> n > 0 \<and> (odd n \<and> a \<le> 0 \<or> even n \<and> a = 0)" |
513 |
unfolding not_less [symmetric] zero_less_power_eq by auto |
|
514 |
||
515 |
lemma power_even_abs: "even n \<Longrightarrow> \<bar>a\<bar> ^ n = a ^ n" |
|
58689 | 516 |
using power_abs [of a n] by (simp add: zero_le_even_power) |
517 |
||
518 |
lemma power_mono_even: |
|
519 |
assumes "even n" and "\<bar>a\<bar> \<le> \<bar>b\<bar>" |
|
520 |
shows "a ^ n \<le> b ^ n" |
|
521 |
proof - |
|
522 |
have "0 \<le> \<bar>a\<bar>" by auto |
|
63654 | 523 |
with \<open>\<bar>a\<bar> \<le> \<bar>b\<bar>\<close> have "\<bar>a\<bar> ^ n \<le> \<bar>b\<bar> ^ n" |
524 |
by (rule power_mono) |
|
525 |
with \<open>even n\<close> show ?thesis |
|
526 |
by (simp add: power_even_abs) |
|
58689 | 527 |
qed |
528 |
||
529 |
lemma power_mono_odd: |
|
530 |
assumes "odd n" and "a \<le> b" |
|
531 |
shows "a ^ n \<le> b ^ n" |
|
532 |
proof (cases "b < 0") |
|
63654 | 533 |
case True |
534 |
with \<open>a \<le> b\<close> have "- b \<le> - a" and "0 \<le> - b" by auto |
|
535 |
then have "(- b) ^ n \<le> (- a) ^ n" by (rule power_mono) |
|
60758 | 536 |
with \<open>odd n\<close> show ?thesis by simp |
58689 | 537 |
next |
63654 | 538 |
case False |
539 |
then have "0 \<le> b" by auto |
|
58689 | 540 |
show ?thesis |
541 |
proof (cases "a < 0") |
|
63654 | 542 |
case True |
543 |
then have "n \<noteq> 0" and "a \<le> 0" using \<open>odd n\<close> [THEN odd_pos] by auto |
|
60758 | 544 |
then have "a ^ n \<le> 0" unfolding power_le_zero_eq using \<open>odd n\<close> by auto |
63654 | 545 |
moreover from \<open>0 \<le> b\<close> have "0 \<le> b ^ n" by auto |
58689 | 546 |
ultimately show ?thesis by auto |
547 |
next |
|
63654 | 548 |
case False |
549 |
then have "0 \<le> a" by auto |
|
550 |
with \<open>a \<le> b\<close> show ?thesis |
|
551 |
using power_mono by auto |
|
58689 | 552 |
qed |
553 |
qed |
|
62083 | 554 |
|
60758 | 555 |
text \<open>Simplify, when the exponent is a numeral\<close> |
58689 | 556 |
|
557 |
lemma zero_le_power_eq_numeral [simp]: |
|
558 |
"0 \<le> a ^ numeral w \<longleftrightarrow> even (numeral w :: nat) \<or> odd (numeral w :: nat) \<and> 0 \<le> a" |
|
559 |
by (fact zero_le_power_eq) |
|
560 |
||
561 |
lemma zero_less_power_eq_numeral [simp]: |
|
63654 | 562 |
"0 < a ^ numeral w \<longleftrightarrow> |
563 |
numeral w = (0 :: nat) \<or> |
|
564 |
even (numeral w :: nat) \<and> a \<noteq> 0 \<or> |
|
565 |
odd (numeral w :: nat) \<and> 0 < a" |
|
58689 | 566 |
by (fact zero_less_power_eq) |
567 |
||
568 |
lemma power_le_zero_eq_numeral [simp]: |
|
63654 | 569 |
"a ^ numeral w \<le> 0 \<longleftrightarrow> |
570 |
(0 :: nat) < numeral w \<and> |
|
571 |
(odd (numeral w :: nat) \<and> a \<le> 0 \<or> even (numeral w :: nat) \<and> a = 0)" |
|
58689 | 572 |
by (fact power_le_zero_eq) |
573 |
||
574 |
lemma power_less_zero_eq_numeral [simp]: |
|
575 |
"a ^ numeral w < 0 \<longleftrightarrow> odd (numeral w :: nat) \<and> a < 0" |
|
576 |
by (fact power_less_zero_eq) |
|
577 |
||
578 |
lemma power_even_abs_numeral [simp]: |
|
579 |
"even (numeral w :: nat) \<Longrightarrow> \<bar>a\<bar> ^ numeral w = a ^ numeral w" |
|
580 |
by (fact power_even_abs) |
|
581 |
||
582 |
end |
|
583 |
||
66816
212a3334e7da
more fundamental definition of div and mod on int
haftmann
parents:
66815
diff
changeset
|
584 |
|
212a3334e7da
more fundamental definition of div and mod on int
haftmann
parents:
66815
diff
changeset
|
585 |
subsection \<open>Instance for @{typ int}\<close> |
212a3334e7da
more fundamental definition of div and mod on int
haftmann
parents:
66815
diff
changeset
|
586 |
|
212a3334e7da
more fundamental definition of div and mod on int
haftmann
parents:
66815
diff
changeset
|
587 |
instance int :: ring_parity |
66839 | 588 |
by standard (simp_all add: dvd_eq_mod_eq_0 divide_int_def division_segment_int_def) |
66816
212a3334e7da
more fundamental definition of div and mod on int
haftmann
parents:
66815
diff
changeset
|
589 |
|
212a3334e7da
more fundamental definition of div and mod on int
haftmann
parents:
66815
diff
changeset
|
590 |
lemma even_diff_iff [simp]: |
212a3334e7da
more fundamental definition of div and mod on int
haftmann
parents:
66815
diff
changeset
|
591 |
"even (k - l) \<longleftrightarrow> even (k + l)" for k l :: int |
212a3334e7da
more fundamental definition of div and mod on int
haftmann
parents:
66815
diff
changeset
|
592 |
using dvd_add_times_triv_right_iff [of 2 "k - l" l] by (simp add: mult_2_right) |
212a3334e7da
more fundamental definition of div and mod on int
haftmann
parents:
66815
diff
changeset
|
593 |
|
212a3334e7da
more fundamental definition of div and mod on int
haftmann
parents:
66815
diff
changeset
|
594 |
lemma even_abs_add_iff [simp]: |
212a3334e7da
more fundamental definition of div and mod on int
haftmann
parents:
66815
diff
changeset
|
595 |
"even (\<bar>k\<bar> + l) \<longleftrightarrow> even (k + l)" for k l :: int |
212a3334e7da
more fundamental definition of div and mod on int
haftmann
parents:
66815
diff
changeset
|
596 |
by (cases "k \<ge> 0") (simp_all add: ac_simps) |
212a3334e7da
more fundamental definition of div and mod on int
haftmann
parents:
66815
diff
changeset
|
597 |
|
212a3334e7da
more fundamental definition of div and mod on int
haftmann
parents:
66815
diff
changeset
|
598 |
lemma even_add_abs_iff [simp]: |
212a3334e7da
more fundamental definition of div and mod on int
haftmann
parents:
66815
diff
changeset
|
599 |
"even (k + \<bar>l\<bar>) \<longleftrightarrow> even (k + l)" for k l :: int |
212a3334e7da
more fundamental definition of div and mod on int
haftmann
parents:
66815
diff
changeset
|
600 |
using even_abs_add_iff [of l k] by (simp add: ac_simps) |
212a3334e7da
more fundamental definition of div and mod on int
haftmann
parents:
66815
diff
changeset
|
601 |
|
212a3334e7da
more fundamental definition of div and mod on int
haftmann
parents:
66815
diff
changeset
|
602 |
lemma even_nat_iff: "0 \<le> k \<Longrightarrow> even (nat k) \<longleftrightarrow> even k" |
212a3334e7da
more fundamental definition of div and mod on int
haftmann
parents:
66815
diff
changeset
|
603 |
by (simp add: even_of_nat [of "nat k", where ?'a = int, symmetric]) |
212a3334e7da
more fundamental definition of div and mod on int
haftmann
parents:
66815
diff
changeset
|
604 |
|
58770 | 605 |
end |