src/HOL/Euclidean_Division.thy
author haftmann
Sun Oct 08 22:28:21 2017 +0200 (20 months ago)
changeset 66808 1907167b6038
parent 66807 c3631f32dfeb
child 66810 cc2b490f9dc4
permissions -rw-r--r--
elementary definition of division on natural numbers
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(*  Title:      HOL/Euclidean_Division.thy
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    Author:     Manuel Eberl, TU Muenchen
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    Author:     Florian Haftmann, TU Muenchen
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*)
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section \<open>Uniquely determined division in euclidean (semi)rings\<close>
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theory Euclidean_Division
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  imports Nat_Transfer Lattices_Big
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begin
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subsection \<open>Prelude: simproc for cancelling @{const divide} and @{const modulo}\<close>
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lemma (in semiring_modulo) cancel_div_mod_rules:
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  "((a div b) * b + a mod b) + c = a + c"
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  "(b * (a div b) + a mod b) + c = a + c"
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  by (simp_all add: div_mult_mod_eq mult_div_mod_eq)
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ML_file "~~/src/Provers/Arith/cancel_div_mod.ML"
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subsection \<open>Euclidean (semi)rings with explicit division and remainder\<close>
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class euclidean_semiring = semidom_modulo + normalization_semidom + 
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  fixes euclidean_size :: "'a \<Rightarrow> nat"
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  assumes size_0 [simp]: "euclidean_size 0 = 0"
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  assumes mod_size_less: 
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    "b \<noteq> 0 \<Longrightarrow> euclidean_size (a mod b) < euclidean_size b"
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  assumes size_mult_mono:
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    "b \<noteq> 0 \<Longrightarrow> euclidean_size a \<le> euclidean_size (a * b)"
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begin
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lemma size_mult_mono': "b \<noteq> 0 \<Longrightarrow> euclidean_size a \<le> euclidean_size (b * a)"
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  by (subst mult.commute) (rule size_mult_mono)
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lemma euclidean_size_normalize [simp]:
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  "euclidean_size (normalize a) = euclidean_size a"
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proof (cases "a = 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 [simp]: False
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  have "euclidean_size (normalize a) \<le> euclidean_size (normalize a * unit_factor a)"
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    by (rule size_mult_mono) simp
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  moreover have "euclidean_size a \<le> euclidean_size (a * (1 div unit_factor a))"
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    by (rule size_mult_mono) simp
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  ultimately show ?thesis
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    by simp
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qed
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lemma dvd_euclidean_size_eq_imp_dvd:
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  assumes "a \<noteq> 0" and "euclidean_size a = euclidean_size b"
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    and "b dvd a" 
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  shows "a dvd b"
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proof (rule ccontr)
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  assume "\<not> a dvd b"
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  hence "b mod a \<noteq> 0" using mod_0_imp_dvd [of b a] by blast
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  then have "b mod a \<noteq> 0" by (simp add: mod_eq_0_iff_dvd)
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  from \<open>b dvd a\<close> have "b dvd b mod a" by (simp add: dvd_mod_iff)
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  then obtain c where "b mod a = b * c" unfolding dvd_def by blast
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    with \<open>b mod a \<noteq> 0\<close> have "c \<noteq> 0" by auto
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  with \<open>b mod a = b * c\<close> have "euclidean_size (b mod a) \<ge> euclidean_size b"
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    using size_mult_mono by force
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  moreover from \<open>\<not> a dvd b\<close> and \<open>a \<noteq> 0\<close>
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  have "euclidean_size (b mod a) < euclidean_size a"
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    using mod_size_less by blast
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  ultimately show False using \<open>euclidean_size a = euclidean_size b\<close>
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    by simp
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qed
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lemma euclidean_size_times_unit:
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  assumes "is_unit a"
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  shows   "euclidean_size (a * b) = euclidean_size b"
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proof (rule antisym)
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  from assms have [simp]: "a \<noteq> 0" by auto
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  thus "euclidean_size (a * b) \<ge> euclidean_size b" by (rule size_mult_mono')
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  from assms have "is_unit (1 div a)" by simp
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  hence "1 div a \<noteq> 0" by (intro notI) simp_all
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  hence "euclidean_size (a * b) \<le> euclidean_size ((1 div a) * (a * b))"
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    by (rule size_mult_mono')
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  also from assms have "(1 div a) * (a * b) = b"
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    by (simp add: algebra_simps unit_div_mult_swap)
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  finally show "euclidean_size (a * b) \<le> euclidean_size b" .
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qed
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lemma euclidean_size_unit:
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  "is_unit a \<Longrightarrow> euclidean_size a = euclidean_size 1"
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  using euclidean_size_times_unit [of a 1] by simp
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lemma unit_iff_euclidean_size: 
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  "is_unit a \<longleftrightarrow> euclidean_size a = euclidean_size 1 \<and> a \<noteq> 0"
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proof safe
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  assume A: "a \<noteq> 0" and B: "euclidean_size a = euclidean_size 1"
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  show "is_unit a"
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    by (rule dvd_euclidean_size_eq_imp_dvd [OF A B]) simp_all
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qed (auto intro: euclidean_size_unit)
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lemma euclidean_size_times_nonunit:
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  assumes "a \<noteq> 0" "b \<noteq> 0" "\<not> is_unit a"
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  shows   "euclidean_size b < euclidean_size (a * b)"
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proof (rule ccontr)
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  assume "\<not>euclidean_size b < euclidean_size (a * b)"
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  with size_mult_mono'[OF assms(1), of b] 
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    have eq: "euclidean_size (a * b) = euclidean_size b" by simp
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  have "a * b dvd b"
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    by (rule dvd_euclidean_size_eq_imp_dvd [OF _ eq]) (insert assms, simp_all)
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  hence "a * b dvd 1 * b" by simp
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  with \<open>b \<noteq> 0\<close> have "is_unit a" by (subst (asm) dvd_times_right_cancel_iff)
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  with assms(3) show False by contradiction
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qed
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lemma dvd_imp_size_le:
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  assumes "a dvd b" "b \<noteq> 0" 
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  shows   "euclidean_size a \<le> euclidean_size b"
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  using assms by (auto elim!: dvdE simp: size_mult_mono)
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lemma dvd_proper_imp_size_less:
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  assumes "a dvd b" "\<not> b dvd a" "b \<noteq> 0" 
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  shows   "euclidean_size a < euclidean_size b"
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proof -
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  from assms(1) obtain c where "b = a * c" by (erule dvdE)
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  hence z: "b = c * a" by (simp add: mult.commute)
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  from z assms have "\<not>is_unit c" by (auto simp: mult.commute mult_unit_dvd_iff)
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  with z assms show ?thesis
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    by (auto intro!: euclidean_size_times_nonunit)
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qed
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lemma unit_imp_mod_eq_0:
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  "a mod b = 0" if "is_unit b"
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  using that by (simp add: mod_eq_0_iff_dvd unit_imp_dvd)
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end
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class euclidean_ring = idom_modulo + euclidean_semiring
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subsection \<open>Euclidean (semi)rings with cancel rules\<close>
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class euclidean_semiring_cancel = euclidean_semiring +
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  assumes div_mult_self1 [simp]: "b \<noteq> 0 \<Longrightarrow> (a + c * b) div b = c + a div b"
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  and div_mult_mult1 [simp]: "c \<noteq> 0 \<Longrightarrow> (c * a) div (c * b) = a div b"
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begin
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lemma div_mult_self2 [simp]:
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  assumes "b \<noteq> 0"
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  shows "(a + b * c) div b = c + a div b"
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  using assms div_mult_self1 [of b a c] by (simp add: mult.commute)
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lemma div_mult_self3 [simp]:
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  assumes "b \<noteq> 0"
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  shows "(c * b + a) div b = c + a div b"
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  using assms by (simp add: add.commute)
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lemma div_mult_self4 [simp]:
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  assumes "b \<noteq> 0"
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  shows "(b * c + a) div b = c + a div b"
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  using assms by (simp add: add.commute)
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lemma mod_mult_self1 [simp]: "(a + c * b) mod b = a mod b"
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proof (cases "b = 0")
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  case True then show ?thesis by simp
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next
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  case False
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  have "a + c * b = (a + c * b) div b * b + (a + c * b) mod b"
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    by (simp add: div_mult_mod_eq)
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  also from False div_mult_self1 [of b a c] have
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    "\<dots> = (c + a div b) * b + (a + c * b) mod b"
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      by (simp add: algebra_simps)
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  finally have "a = a div b * b + (a + c * b) mod b"
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    by (simp add: add.commute [of a] add.assoc distrib_right)
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  then have "a div b * b + (a + c * b) mod b = a div b * b + a mod b"
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    by (simp add: div_mult_mod_eq)
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  then show ?thesis by simp
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qed
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lemma mod_mult_self2 [simp]:
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  "(a + b * c) mod b = a mod b"
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  by (simp add: mult.commute [of b])
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lemma mod_mult_self3 [simp]:
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  "(c * b + a) mod b = a mod b"
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  by (simp add: add.commute)
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lemma mod_mult_self4 [simp]:
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  "(b * c + a) mod b = a mod b"
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  by (simp add: add.commute)
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lemma mod_mult_self1_is_0 [simp]:
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  "b * a mod b = 0"
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  using mod_mult_self2 [of 0 b a] by simp
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lemma mod_mult_self2_is_0 [simp]:
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  "a * b mod b = 0"
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  using mod_mult_self1 [of 0 a b] by simp
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lemma div_add_self1:
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  assumes "b \<noteq> 0"
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  shows "(b + a) div b = a div b + 1"
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  using assms div_mult_self1 [of b a 1] by (simp add: add.commute)
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lemma div_add_self2:
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  assumes "b \<noteq> 0"
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  shows "(a + b) div b = a div b + 1"
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  using assms div_add_self1 [of b a] by (simp add: add.commute)
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lemma mod_add_self1 [simp]:
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  "(b + a) mod b = a mod b"
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  using mod_mult_self1 [of a 1 b] by (simp add: add.commute)
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lemma mod_add_self2 [simp]:
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  "(a + b) mod b = a mod b"
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  using mod_mult_self1 [of a 1 b] by simp
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lemma mod_div_trivial [simp]:
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  "a mod b div b = 0"
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proof (cases "b = 0")
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  assume "b = 0"
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  thus ?thesis by simp
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next
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  assume "b \<noteq> 0"
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  hence "a div b + a mod b div b = (a mod b + a div b * b) div b"
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    by (rule div_mult_self1 [symmetric])
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  also have "\<dots> = a div b"
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    by (simp only: mod_div_mult_eq)
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  also have "\<dots> = a div b + 0"
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    by simp
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  finally show ?thesis
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    by (rule add_left_imp_eq)
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qed
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lemma mod_mod_trivial [simp]:
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  "a mod b mod b = a mod b"
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proof -
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  have "a mod b mod b = (a mod b + a div b * b) mod b"
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    by (simp only: mod_mult_self1)
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  also have "\<dots> = a mod b"
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    by (simp only: mod_div_mult_eq)
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  finally show ?thesis .
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qed
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lemma mod_mod_cancel:
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  assumes "c dvd b"
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  shows "a mod b mod c = a mod c"
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proof -
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  from \<open>c dvd b\<close> obtain k where "b = c * k"
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    by (rule dvdE)
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  have "a mod b mod c = a mod (c * k) mod c"
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    by (simp only: \<open>b = c * k\<close>)
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  also have "\<dots> = (a mod (c * k) + a div (c * k) * k * c) mod c"
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    by (simp only: mod_mult_self1)
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  also have "\<dots> = (a div (c * k) * (c * k) + a mod (c * k)) mod c"
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    by (simp only: ac_simps)
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  also have "\<dots> = a mod c"
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    by (simp only: div_mult_mod_eq)
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  finally show ?thesis .
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qed
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lemma div_mult_mult2 [simp]:
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  "c \<noteq> 0 \<Longrightarrow> (a * c) div (b * c) = a div b"
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  by (drule div_mult_mult1) (simp add: mult.commute)
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lemma div_mult_mult1_if [simp]:
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  "(c * a) div (c * b) = (if c = 0 then 0 else a div b)"
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  by simp_all
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lemma mod_mult_mult1:
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  "(c * a) mod (c * b) = c * (a mod b)"
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proof (cases "c = 0")
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  case True then show ?thesis by simp
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next
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  case False
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  from div_mult_mod_eq
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  have "((c * a) div (c * b)) * (c * b) + (c * a) mod (c * b) = c * a" .
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  with False have "c * ((a div b) * b + a mod b) + (c * a) mod (c * b)
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    = c * a + c * (a mod b)" by (simp add: algebra_simps)
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  with div_mult_mod_eq show ?thesis by simp
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qed
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lemma mod_mult_mult2:
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  "(a * c) mod (b * c) = (a mod b) * c"
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  using mod_mult_mult1 [of c a b] by (simp add: mult.commute)
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lemma mult_mod_left: "(a mod b) * c = (a * c) mod (b * c)"
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  by (fact mod_mult_mult2 [symmetric])
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lemma mult_mod_right: "c * (a mod b) = (c * a) mod (c * b)"
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  by (fact mod_mult_mult1 [symmetric])
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lemma dvd_mod: "k dvd m \<Longrightarrow> k dvd n \<Longrightarrow> k dvd (m mod n)"
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  unfolding dvd_def by (auto simp add: mod_mult_mult1)
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lemma div_plus_div_distrib_dvd_left:
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  "c dvd a \<Longrightarrow> (a + b) div c = a div c + b div c"
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  by (cases "c = 0") (auto elim: dvdE)
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lemma div_plus_div_distrib_dvd_right:
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  "c dvd b \<Longrightarrow> (a + b) div c = a div c + b div c"
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  using div_plus_div_distrib_dvd_left [of c b a]
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  by (simp add: ac_simps)
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named_theorems mod_simps
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   304
text \<open>Addition respects modular equivalence.\<close>
haftmann@66806
   305
haftmann@66806
   306
lemma mod_add_left_eq [mod_simps]:
haftmann@66806
   307
  "(a mod c + b) mod c = (a + b) mod c"
haftmann@66806
   308
proof -
haftmann@66806
   309
  have "(a + b) mod c = (a div c * c + a mod c + b) mod c"
haftmann@66806
   310
    by (simp only: div_mult_mod_eq)
haftmann@66806
   311
  also have "\<dots> = (a mod c + b + a div c * c) mod c"
haftmann@66806
   312
    by (simp only: ac_simps)
haftmann@66806
   313
  also have "\<dots> = (a mod c + b) mod c"
haftmann@66806
   314
    by (rule mod_mult_self1)
haftmann@66806
   315
  finally show ?thesis
haftmann@66806
   316
    by (rule sym)
haftmann@66806
   317
qed
haftmann@66806
   318
haftmann@66806
   319
lemma mod_add_right_eq [mod_simps]:
haftmann@66806
   320
  "(a + b mod c) mod c = (a + b) mod c"
haftmann@66806
   321
  using mod_add_left_eq [of b c a] by (simp add: ac_simps)
haftmann@66806
   322
haftmann@66806
   323
lemma mod_add_eq:
haftmann@66806
   324
  "(a mod c + b mod c) mod c = (a + b) mod c"
haftmann@66806
   325
  by (simp add: mod_add_left_eq mod_add_right_eq)
haftmann@66806
   326
haftmann@66806
   327
lemma mod_sum_eq [mod_simps]:
haftmann@66806
   328
  "(\<Sum>i\<in>A. f i mod a) mod a = sum f A mod a"
haftmann@66806
   329
proof (induct A rule: infinite_finite_induct)
haftmann@66806
   330
  case (insert i A)
haftmann@66806
   331
  then have "(\<Sum>i\<in>insert i A. f i mod a) mod a
haftmann@66806
   332
    = (f i mod a + (\<Sum>i\<in>A. f i mod a)) mod a"
haftmann@66806
   333
    by simp
haftmann@66806
   334
  also have "\<dots> = (f i + (\<Sum>i\<in>A. f i mod a) mod a) mod a"
haftmann@66806
   335
    by (simp add: mod_simps)
haftmann@66806
   336
  also have "\<dots> = (f i + (\<Sum>i\<in>A. f i) mod a) mod a"
haftmann@66806
   337
    by (simp add: insert.hyps)
haftmann@66806
   338
  finally show ?case
haftmann@66806
   339
    by (simp add: insert.hyps mod_simps)
haftmann@66806
   340
qed simp_all
haftmann@66806
   341
haftmann@66806
   342
lemma mod_add_cong:
haftmann@66806
   343
  assumes "a mod c = a' mod c"
haftmann@66806
   344
  assumes "b mod c = b' mod c"
haftmann@66806
   345
  shows "(a + b) mod c = (a' + b') mod c"
haftmann@66806
   346
proof -
haftmann@66806
   347
  have "(a mod c + b mod c) mod c = (a' mod c + b' mod c) mod c"
haftmann@66806
   348
    unfolding assms ..
haftmann@66806
   349
  then show ?thesis
haftmann@66806
   350
    by (simp add: mod_add_eq)
haftmann@66806
   351
qed
haftmann@66806
   352
haftmann@66806
   353
text \<open>Multiplication respects modular equivalence.\<close>
haftmann@66806
   354
haftmann@66806
   355
lemma mod_mult_left_eq [mod_simps]:
haftmann@66806
   356
  "((a mod c) * b) mod c = (a * b) mod c"
haftmann@66806
   357
proof -
haftmann@66806
   358
  have "(a * b) mod c = ((a div c * c + a mod c) * b) mod c"
haftmann@66806
   359
    by (simp only: div_mult_mod_eq)
haftmann@66806
   360
  also have "\<dots> = (a mod c * b + a div c * b * c) mod c"
haftmann@66806
   361
    by (simp only: algebra_simps)
haftmann@66806
   362
  also have "\<dots> = (a mod c * b) mod c"
haftmann@66806
   363
    by (rule mod_mult_self1)
haftmann@66806
   364
  finally show ?thesis
haftmann@66806
   365
    by (rule sym)
haftmann@66806
   366
qed
haftmann@66806
   367
haftmann@66806
   368
lemma mod_mult_right_eq [mod_simps]:
haftmann@66806
   369
  "(a * (b mod c)) mod c = (a * b) mod c"
haftmann@66806
   370
  using mod_mult_left_eq [of b c a] by (simp add: ac_simps)
haftmann@66806
   371
haftmann@66806
   372
lemma mod_mult_eq:
haftmann@66806
   373
  "((a mod c) * (b mod c)) mod c = (a * b) mod c"
haftmann@66806
   374
  by (simp add: mod_mult_left_eq mod_mult_right_eq)
haftmann@66806
   375
haftmann@66806
   376
lemma mod_prod_eq [mod_simps]:
haftmann@66806
   377
  "(\<Prod>i\<in>A. f i mod a) mod a = prod f A mod a"
haftmann@66806
   378
proof (induct A rule: infinite_finite_induct)
haftmann@66806
   379
  case (insert i A)
haftmann@66806
   380
  then have "(\<Prod>i\<in>insert i A. f i mod a) mod a
haftmann@66806
   381
    = (f i mod a * (\<Prod>i\<in>A. f i mod a)) mod a"
haftmann@66806
   382
    by simp
haftmann@66806
   383
  also have "\<dots> = (f i * ((\<Prod>i\<in>A. f i mod a) mod a)) mod a"
haftmann@66806
   384
    by (simp add: mod_simps)
haftmann@66806
   385
  also have "\<dots> = (f i * ((\<Prod>i\<in>A. f i) mod a)) mod a"
haftmann@66806
   386
    by (simp add: insert.hyps)
haftmann@66806
   387
  finally show ?case
haftmann@66806
   388
    by (simp add: insert.hyps mod_simps)
haftmann@66806
   389
qed simp_all
haftmann@66806
   390
haftmann@66806
   391
lemma mod_mult_cong:
haftmann@66806
   392
  assumes "a mod c = a' mod c"
haftmann@66806
   393
  assumes "b mod c = b' mod c"
haftmann@66806
   394
  shows "(a * b) mod c = (a' * b') mod c"
haftmann@66806
   395
proof -
haftmann@66806
   396
  have "(a mod c * (b mod c)) mod c = (a' mod c * (b' mod c)) mod c"
haftmann@66806
   397
    unfolding assms ..
haftmann@66806
   398
  then show ?thesis
haftmann@66806
   399
    by (simp add: mod_mult_eq)
haftmann@66806
   400
qed
haftmann@66806
   401
haftmann@66806
   402
text \<open>Exponentiation respects modular equivalence.\<close>
haftmann@66806
   403
haftmann@66806
   404
lemma power_mod [mod_simps]: 
haftmann@66806
   405
  "((a mod b) ^ n) mod b = (a ^ n) mod b"
haftmann@66806
   406
proof (induct n)
haftmann@66806
   407
  case 0
haftmann@66806
   408
  then show ?case by simp
haftmann@66806
   409
next
haftmann@66806
   410
  case (Suc n)
haftmann@66806
   411
  have "(a mod b) ^ Suc n mod b = (a mod b) * ((a mod b) ^ n mod b) mod b"
haftmann@66806
   412
    by (simp add: mod_mult_right_eq)
haftmann@66806
   413
  with Suc show ?case
haftmann@66806
   414
    by (simp add: mod_mult_left_eq mod_mult_right_eq)
haftmann@66806
   415
qed
haftmann@66806
   416
haftmann@66806
   417
end
haftmann@66806
   418
haftmann@66806
   419
haftmann@66806
   420
class euclidean_ring_cancel = euclidean_ring + euclidean_semiring_cancel
haftmann@66806
   421
begin
haftmann@66806
   422
haftmann@66806
   423
subclass idom_divide ..
haftmann@66806
   424
haftmann@66806
   425
lemma div_minus_minus [simp]: "(- a) div (- b) = a div b"
haftmann@66806
   426
  using div_mult_mult1 [of "- 1" a b] by simp
haftmann@66806
   427
haftmann@66806
   428
lemma mod_minus_minus [simp]: "(- a) mod (- b) = - (a mod b)"
haftmann@66806
   429
  using mod_mult_mult1 [of "- 1" a b] by simp
haftmann@66806
   430
haftmann@66806
   431
lemma div_minus_right: "a div (- b) = (- a) div b"
haftmann@66806
   432
  using div_minus_minus [of "- a" b] by simp
haftmann@66806
   433
haftmann@66806
   434
lemma mod_minus_right: "a mod (- b) = - ((- a) mod b)"
haftmann@66806
   435
  using mod_minus_minus [of "- a" b] by simp
haftmann@66806
   436
haftmann@66806
   437
lemma div_minus1_right [simp]: "a div (- 1) = - a"
haftmann@66806
   438
  using div_minus_right [of a 1] by simp
haftmann@66806
   439
haftmann@66806
   440
lemma mod_minus1_right [simp]: "a mod (- 1) = 0"
haftmann@66806
   441
  using mod_minus_right [of a 1] by simp
haftmann@66806
   442
haftmann@66806
   443
text \<open>Negation respects modular equivalence.\<close>
haftmann@66806
   444
haftmann@66806
   445
lemma mod_minus_eq [mod_simps]:
haftmann@66806
   446
  "(- (a mod b)) mod b = (- a) mod b"
haftmann@66806
   447
proof -
haftmann@66806
   448
  have "(- a) mod b = (- (a div b * b + a mod b)) mod b"
haftmann@66806
   449
    by (simp only: div_mult_mod_eq)
haftmann@66806
   450
  also have "\<dots> = (- (a mod b) + - (a div b) * b) mod b"
haftmann@66806
   451
    by (simp add: ac_simps)
haftmann@66806
   452
  also have "\<dots> = (- (a mod b)) mod b"
haftmann@66806
   453
    by (rule mod_mult_self1)
haftmann@66806
   454
  finally show ?thesis
haftmann@66806
   455
    by (rule sym)
haftmann@66806
   456
qed
haftmann@66806
   457
haftmann@66806
   458
lemma mod_minus_cong:
haftmann@66806
   459
  assumes "a mod b = a' mod b"
haftmann@66806
   460
  shows "(- a) mod b = (- a') mod b"
haftmann@66806
   461
proof -
haftmann@66806
   462
  have "(- (a mod b)) mod b = (- (a' mod b)) mod b"
haftmann@66806
   463
    unfolding assms ..
haftmann@66806
   464
  then show ?thesis
haftmann@66806
   465
    by (simp add: mod_minus_eq)
haftmann@66806
   466
qed
haftmann@66806
   467
haftmann@66806
   468
text \<open>Subtraction respects modular equivalence.\<close>
haftmann@66806
   469
haftmann@66806
   470
lemma mod_diff_left_eq [mod_simps]:
haftmann@66806
   471
  "(a mod c - b) mod c = (a - b) mod c"
haftmann@66806
   472
  using mod_add_cong [of a c "a mod c" "- b" "- b"]
haftmann@66806
   473
  by simp
haftmann@66806
   474
haftmann@66806
   475
lemma mod_diff_right_eq [mod_simps]:
haftmann@66806
   476
  "(a - b mod c) mod c = (a - b) mod c"
haftmann@66806
   477
  using mod_add_cong [of a c a "- b" "- (b mod c)"] mod_minus_cong [of "b mod c" c b]
haftmann@66806
   478
  by simp
haftmann@66806
   479
haftmann@66806
   480
lemma mod_diff_eq:
haftmann@66806
   481
  "(a mod c - b mod c) mod c = (a - b) mod c"
haftmann@66806
   482
  using mod_add_cong [of a c "a mod c" "- b" "- (b mod c)"] mod_minus_cong [of "b mod c" c b]
haftmann@66806
   483
  by simp
haftmann@66806
   484
haftmann@66806
   485
lemma mod_diff_cong:
haftmann@66806
   486
  assumes "a mod c = a' mod c"
haftmann@66806
   487
  assumes "b mod c = b' mod c"
haftmann@66806
   488
  shows "(a - b) mod c = (a' - b') mod c"
haftmann@66806
   489
  using assms mod_add_cong [of a c a' "- b" "- b'"] mod_minus_cong [of b c "b'"]
haftmann@66806
   490
  by simp
haftmann@66806
   491
haftmann@66806
   492
lemma minus_mod_self2 [simp]:
haftmann@66806
   493
  "(a - b) mod b = a mod b"
haftmann@66806
   494
  using mod_diff_right_eq [of a b b]
haftmann@66806
   495
  by (simp add: mod_diff_right_eq)
haftmann@66806
   496
haftmann@66806
   497
lemma minus_mod_self1 [simp]:
haftmann@66806
   498
  "(b - a) mod b = - a mod b"
haftmann@66806
   499
  using mod_add_self2 [of "- a" b] by simp
haftmann@66806
   500
haftmann@66806
   501
lemma mod_eq_dvd_iff:
haftmann@66806
   502
  "a mod c = b mod c \<longleftrightarrow> c dvd a - b" (is "?P \<longleftrightarrow> ?Q")
haftmann@66806
   503
proof
haftmann@66806
   504
  assume ?P
haftmann@66806
   505
  then have "(a mod c - b mod c) mod c = 0"
haftmann@66806
   506
    by simp
haftmann@66806
   507
  then show ?Q
haftmann@66806
   508
    by (simp add: dvd_eq_mod_eq_0 mod_simps)
haftmann@66806
   509
next
haftmann@66806
   510
  assume ?Q
haftmann@66806
   511
  then obtain d where d: "a - b = c * d" ..
haftmann@66806
   512
  then have "a = c * d + b"
haftmann@66806
   513
    by (simp add: algebra_simps)
haftmann@66806
   514
  then show ?P by simp
haftmann@66806
   515
qed
haftmann@66806
   516
haftmann@66806
   517
end
haftmann@66806
   518
haftmann@66806
   519
  
haftmann@64785
   520
subsection \<open>Uniquely determined division\<close>
haftmann@64785
   521
  
haftmann@64785
   522
class unique_euclidean_semiring = euclidean_semiring + 
haftmann@64785
   523
  fixes uniqueness_constraint :: "'a \<Rightarrow> 'a \<Rightarrow> bool"
haftmann@64785
   524
  assumes size_mono_mult:
haftmann@64785
   525
    "b \<noteq> 0 \<Longrightarrow> euclidean_size a < euclidean_size c
haftmann@64785
   526
      \<Longrightarrow> euclidean_size (a * b) < euclidean_size (c * b)"
haftmann@64785
   527
    -- \<open>FIXME justify\<close>
haftmann@64785
   528
  assumes uniqueness_constraint_mono_mult:
haftmann@64785
   529
    "uniqueness_constraint a b \<Longrightarrow> uniqueness_constraint (a * c) (b * c)"
haftmann@64785
   530
  assumes uniqueness_constraint_mod:
haftmann@64785
   531
    "b \<noteq> 0 \<Longrightarrow> \<not> b dvd a \<Longrightarrow> uniqueness_constraint (a mod b) b"
haftmann@64785
   532
  assumes div_bounded:
haftmann@64785
   533
    "b \<noteq> 0 \<Longrightarrow> uniqueness_constraint r b
haftmann@64785
   534
    \<Longrightarrow> euclidean_size r < euclidean_size b
haftmann@64785
   535
    \<Longrightarrow> (q * b + r) div b = q"
haftmann@64785
   536
begin
haftmann@64785
   537
haftmann@64785
   538
lemma divmod_cases [case_names divides remainder by0]:
haftmann@64785
   539
  obtains 
haftmann@64785
   540
    (divides) q where "b \<noteq> 0"
haftmann@64785
   541
      and "a div b = q"
haftmann@64785
   542
      and "a mod b = 0"
haftmann@64785
   543
      and "a = q * b"
haftmann@64785
   544
  | (remainder) q r where "b \<noteq> 0" and "r \<noteq> 0"
haftmann@64785
   545
      and "uniqueness_constraint r b"
haftmann@64785
   546
      and "euclidean_size r < euclidean_size b"
haftmann@64785
   547
      and "a div b = q"
haftmann@64785
   548
      and "a mod b = r"
haftmann@64785
   549
      and "a = q * b + r"
haftmann@64785
   550
  | (by0) "b = 0"
haftmann@64785
   551
proof (cases "b = 0")
haftmann@64785
   552
  case True
haftmann@64785
   553
  then show thesis
haftmann@64785
   554
  by (rule by0)
haftmann@64785
   555
next
haftmann@64785
   556
  case False
haftmann@64785
   557
  show thesis
haftmann@64785
   558
  proof (cases "b dvd a")
haftmann@64785
   559
    case True
haftmann@64785
   560
    then obtain q where "a = b * q" ..
haftmann@64785
   561
    with \<open>b \<noteq> 0\<close> divides
haftmann@64785
   562
    show thesis
haftmann@64785
   563
      by (simp add: ac_simps)
haftmann@64785
   564
  next
haftmann@64785
   565
    case False
haftmann@64785
   566
    then have "a mod b \<noteq> 0"
haftmann@64785
   567
      by (simp add: mod_eq_0_iff_dvd)
haftmann@64785
   568
    moreover from \<open>b \<noteq> 0\<close> \<open>\<not> b dvd a\<close> have "uniqueness_constraint (a mod b) b"
haftmann@64785
   569
      by (rule uniqueness_constraint_mod)
haftmann@64785
   570
    moreover have "euclidean_size (a mod b) < euclidean_size b"
haftmann@64785
   571
      using \<open>b \<noteq> 0\<close> by (rule mod_size_less)
haftmann@64785
   572
    moreover have "a = a div b * b + a mod b"
haftmann@64785
   573
      by (simp add: div_mult_mod_eq)
haftmann@64785
   574
    ultimately show thesis
haftmann@64785
   575
      using \<open>b \<noteq> 0\<close> by (blast intro: remainder)
haftmann@64785
   576
  qed
haftmann@64785
   577
qed
haftmann@64785
   578
haftmann@64785
   579
lemma div_eqI:
haftmann@64785
   580
  "a div b = q" if "b \<noteq> 0" "uniqueness_constraint r b"
haftmann@64785
   581
    "euclidean_size r < euclidean_size b" "q * b + r = a"
haftmann@64785
   582
proof -
haftmann@64785
   583
  from that have "(q * b + r) div b = q"
haftmann@64785
   584
    by (auto intro: div_bounded)
haftmann@64785
   585
  with that show ?thesis
haftmann@64785
   586
    by simp
haftmann@64785
   587
qed
haftmann@64785
   588
haftmann@64785
   589
lemma mod_eqI:
haftmann@64785
   590
  "a mod b = r" if "b \<noteq> 0" "uniqueness_constraint r b"
haftmann@64785
   591
    "euclidean_size r < euclidean_size b" "q * b + r = a" 
haftmann@64785
   592
proof -
haftmann@64785
   593
  from that have "a div b = q"
haftmann@64785
   594
    by (rule div_eqI)
haftmann@64785
   595
  moreover have "a div b * b + a mod b = a"
haftmann@64785
   596
    by (fact div_mult_mod_eq)
haftmann@64785
   597
  ultimately have "a div b * b + a mod b = a div b * b + r"
haftmann@64785
   598
    using \<open>q * b + r = a\<close> by simp
haftmann@64785
   599
  then show ?thesis
haftmann@64785
   600
    by simp
haftmann@64785
   601
qed
haftmann@64785
   602
haftmann@66806
   603
subclass euclidean_semiring_cancel
haftmann@66806
   604
proof
haftmann@66806
   605
  show "(a + c * b) div b = c + a div b" if "b \<noteq> 0" for a b c
haftmann@66806
   606
  proof (cases a b rule: divmod_cases)
haftmann@66806
   607
    case by0
haftmann@66806
   608
    with \<open>b \<noteq> 0\<close> show ?thesis
haftmann@66806
   609
      by simp
haftmann@66806
   610
  next
haftmann@66806
   611
    case (divides q)
haftmann@66806
   612
    then show ?thesis
haftmann@66806
   613
      by (simp add: ac_simps)
haftmann@66806
   614
  next
haftmann@66806
   615
    case (remainder q r)
haftmann@66806
   616
    then show ?thesis
haftmann@66806
   617
      by (auto intro: div_eqI simp add: algebra_simps)
haftmann@66806
   618
  qed
haftmann@66806
   619
next
haftmann@66806
   620
  show"(c * a) div (c * b) = a div b" if "c \<noteq> 0" for a b c
haftmann@66806
   621
  proof (cases a b rule: divmod_cases)
haftmann@66806
   622
    case by0
haftmann@66806
   623
    then show ?thesis
haftmann@66806
   624
      by simp
haftmann@66806
   625
  next
haftmann@66806
   626
    case (divides q)
haftmann@66806
   627
    with \<open>c \<noteq> 0\<close> show ?thesis
haftmann@66806
   628
      by (simp add: mult.left_commute [of c])
haftmann@66806
   629
  next
haftmann@66806
   630
    case (remainder q r)
haftmann@66806
   631
    from \<open>b \<noteq> 0\<close> \<open>c \<noteq> 0\<close> have "b * c \<noteq> 0"
haftmann@66806
   632
      by simp
haftmann@66806
   633
    from remainder \<open>c \<noteq> 0\<close>
haftmann@66806
   634
    have "uniqueness_constraint (r * c) (b * c)"
haftmann@66806
   635
      and "euclidean_size (r * c) < euclidean_size (b * c)"
haftmann@66806
   636
      by (simp_all add: uniqueness_constraint_mono_mult uniqueness_constraint_mod size_mono_mult)
haftmann@66806
   637
    with remainder show ?thesis
haftmann@66806
   638
      by (auto intro!: div_eqI [of _ "c * (a mod b)"] simp add: algebra_simps)
haftmann@66806
   639
        (use \<open>b * c \<noteq> 0\<close> in simp)
haftmann@66806
   640
  qed
haftmann@66806
   641
qed
haftmann@66806
   642
haftmann@64785
   643
end
haftmann@64785
   644
haftmann@64785
   645
class unique_euclidean_ring = euclidean_ring + unique_euclidean_semiring
haftmann@66806
   646
begin
haftmann@66806
   647
  
haftmann@66806
   648
subclass euclidean_ring_cancel ..
haftmann@64785
   649
haftmann@64785
   650
end
haftmann@66806
   651
haftmann@66808
   652
haftmann@66808
   653
subsection \<open>Euclidean division on @{typ nat}\<close>
haftmann@66808
   654
haftmann@66808
   655
instantiation nat :: unique_euclidean_semiring
haftmann@66808
   656
begin
haftmann@66808
   657
haftmann@66808
   658
definition normalize_nat :: "nat \<Rightarrow> nat"
haftmann@66808
   659
  where [simp]: "normalize = (id :: nat \<Rightarrow> nat)"
haftmann@66808
   660
haftmann@66808
   661
definition unit_factor_nat :: "nat \<Rightarrow> nat"
haftmann@66808
   662
  where "unit_factor n = (if n = 0 then 0 else 1 :: nat)"
haftmann@66808
   663
haftmann@66808
   664
lemma unit_factor_simps [simp]:
haftmann@66808
   665
  "unit_factor 0 = (0::nat)"
haftmann@66808
   666
  "unit_factor (Suc n) = 1"
haftmann@66808
   667
  by (simp_all add: unit_factor_nat_def)
haftmann@66808
   668
haftmann@66808
   669
definition euclidean_size_nat :: "nat \<Rightarrow> nat"
haftmann@66808
   670
  where [simp]: "euclidean_size_nat = id"
haftmann@66808
   671
haftmann@66808
   672
definition uniqueness_constraint_nat :: "nat \<Rightarrow> nat \<Rightarrow> bool"
haftmann@66808
   673
  where [simp]: "uniqueness_constraint_nat = \<top>"
haftmann@66808
   674
haftmann@66808
   675
definition divide_nat :: "nat \<Rightarrow> nat \<Rightarrow> nat"
haftmann@66808
   676
  where "m div n = (if n = 0 then 0 else Max {k::nat. k * n \<le> m})"
haftmann@66808
   677
haftmann@66808
   678
definition modulo_nat :: "nat \<Rightarrow> nat \<Rightarrow> nat"
haftmann@66808
   679
  where "m mod n = m - (m div n * (n::nat))"
haftmann@66808
   680
haftmann@66808
   681
instance proof
haftmann@66808
   682
  fix m n :: nat
haftmann@66808
   683
  have ex: "\<exists>k. k * n \<le> l" for l :: nat
haftmann@66808
   684
    by (rule exI [of _ 0]) simp
haftmann@66808
   685
  have fin: "finite {k. k * n \<le> l}" if "n > 0" for l
haftmann@66808
   686
  proof -
haftmann@66808
   687
    from that have "{k. k * n \<le> l} \<subseteq> {k. k \<le> l}"
haftmann@66808
   688
      by (cases n) auto
haftmann@66808
   689
    then show ?thesis
haftmann@66808
   690
      by (rule finite_subset) simp
haftmann@66808
   691
  qed
haftmann@66808
   692
  have mult_div_unfold: "n * (m div n) = Max {l. l \<le> m \<and> n dvd l}"
haftmann@66808
   693
  proof (cases "n = 0")
haftmann@66808
   694
    case True
haftmann@66808
   695
    moreover have "{l. l = 0 \<and> l \<le> m} = {0::nat}"
haftmann@66808
   696
      by auto
haftmann@66808
   697
    ultimately show ?thesis
haftmann@66808
   698
      by simp
haftmann@66808
   699
  next
haftmann@66808
   700
    case False
haftmann@66808
   701
    with ex [of m] fin have "n * Max {k. k * n \<le> m} = Max (times n ` {k. k * n \<le> m})"
haftmann@66808
   702
      by (auto simp add: nat_mult_max_right intro: hom_Max_commute)
haftmann@66808
   703
    also have "times n ` {k. k * n \<le> m} = {l. l \<le> m \<and> n dvd l}"
haftmann@66808
   704
      by (auto simp add: ac_simps elim!: dvdE)
haftmann@66808
   705
    finally show ?thesis
haftmann@66808
   706
      using False by (simp add: divide_nat_def ac_simps)
haftmann@66808
   707
  qed
haftmann@66808
   708
  show "n div 0 = 0"
haftmann@66808
   709
    by (simp add: divide_nat_def)
haftmann@66808
   710
  have less_eq: "m div n * n \<le> m"
haftmann@66808
   711
    by (auto simp add: mult_div_unfold ac_simps intro: Max.boundedI)
haftmann@66808
   712
  then show "m div n * n + m mod n = m"
haftmann@66808
   713
    by (simp add: modulo_nat_def)
haftmann@66808
   714
  assume "n \<noteq> 0" 
haftmann@66808
   715
  show "m * n div n = m"
haftmann@66808
   716
    using \<open>n \<noteq> 0\<close> by (auto simp add: divide_nat_def ac_simps intro: Max_eqI)
haftmann@66808
   717
  show "euclidean_size (m mod n) < euclidean_size n"
haftmann@66808
   718
  proof -
haftmann@66808
   719
    have "m < Suc (m div n) * n"
haftmann@66808
   720
    proof (rule ccontr)
haftmann@66808
   721
      assume "\<not> m < Suc (m div n) * n"
haftmann@66808
   722
      then have "Suc (m div n) * n \<le> m"
haftmann@66808
   723
        by (simp add: not_less)
haftmann@66808
   724
      moreover from \<open>n \<noteq> 0\<close> have "Max {k. k * n \<le> m} < Suc (m div n)"
haftmann@66808
   725
        by (simp add: divide_nat_def)
haftmann@66808
   726
      with \<open>n \<noteq> 0\<close> ex fin have "\<And>k. k * n \<le> m \<Longrightarrow> k < Suc (m div n)"
haftmann@66808
   727
        by auto
haftmann@66808
   728
      ultimately have "Suc (m div n) < Suc (m div n)"
haftmann@66808
   729
        by blast
haftmann@66808
   730
      then show False
haftmann@66808
   731
        by simp
haftmann@66808
   732
    qed
haftmann@66808
   733
    with \<open>n \<noteq> 0\<close> show ?thesis
haftmann@66808
   734
      by (simp add: modulo_nat_def)
haftmann@66808
   735
  qed
haftmann@66808
   736
  show "euclidean_size m \<le> euclidean_size (m * n)"
haftmann@66808
   737
    using \<open>n \<noteq> 0\<close> by (cases n) simp_all
haftmann@66808
   738
  fix q r :: nat
haftmann@66808
   739
  show "(q * n + r) div n = q" if "euclidean_size r < euclidean_size n"
haftmann@66808
   740
  proof -
haftmann@66808
   741
    from that have "r < n"
haftmann@66808
   742
      by simp
haftmann@66808
   743
    have "k \<le> q" if "k * n \<le> q * n + r" for k
haftmann@66808
   744
    proof (rule ccontr)
haftmann@66808
   745
      assume "\<not> k \<le> q"
haftmann@66808
   746
      then have "q < k"
haftmann@66808
   747
        by simp
haftmann@66808
   748
      then obtain l where "k = Suc (q + l)"
haftmann@66808
   749
        by (auto simp add: less_iff_Suc_add)
haftmann@66808
   750
      with \<open>r < n\<close> that show False
haftmann@66808
   751
        by (simp add: algebra_simps)
haftmann@66808
   752
    qed
haftmann@66808
   753
    with \<open>n \<noteq> 0\<close> ex fin show ?thesis
haftmann@66808
   754
      by (auto simp add: divide_nat_def Max_eq_iff)
haftmann@66808
   755
  qed
haftmann@66808
   756
qed (simp_all add: unit_factor_nat_def)
haftmann@66808
   757
haftmann@66806
   758
end
haftmann@66808
   759
haftmann@66808
   760
text \<open>Tool support\<close>
haftmann@66808
   761
haftmann@66808
   762
ML \<open>
haftmann@66808
   763
structure Cancel_Div_Mod_Nat = Cancel_Div_Mod
haftmann@66808
   764
(
haftmann@66808
   765
  val div_name = @{const_name divide};
haftmann@66808
   766
  val mod_name = @{const_name modulo};
haftmann@66808
   767
  val mk_binop = HOLogic.mk_binop;
haftmann@66808
   768
  val mk_plus = HOLogic.mk_binop @{const_name Groups.plus};
haftmann@66808
   769
  val dest_plus = HOLogic.dest_bin @{const_name Groups.plus} HOLogic.natT;
haftmann@66808
   770
  fun mk_sum [] = HOLogic.zero
haftmann@66808
   771
    | mk_sum [t] = t
haftmann@66808
   772
    | mk_sum (t :: ts) = mk_plus (t, mk_sum ts);
haftmann@66808
   773
  fun dest_sum tm =
haftmann@66808
   774
    if HOLogic.is_zero tm then []
haftmann@66808
   775
    else
haftmann@66808
   776
      (case try HOLogic.dest_Suc tm of
haftmann@66808
   777
        SOME t => HOLogic.Suc_zero :: dest_sum t
haftmann@66808
   778
      | NONE =>
haftmann@66808
   779
          (case try dest_plus tm of
haftmann@66808
   780
            SOME (t, u) => dest_sum t @ dest_sum u
haftmann@66808
   781
          | NONE => [tm]));
haftmann@66808
   782
haftmann@66808
   783
  val div_mod_eqs = map mk_meta_eq @{thms cancel_div_mod_rules};
haftmann@66808
   784
haftmann@66808
   785
  val prove_eq_sums = Arith_Data.prove_conv2 all_tac
haftmann@66808
   786
    (Arith_Data.simp_all_tac @{thms add_0_left add_0_right ac_simps})
haftmann@66808
   787
)
haftmann@66808
   788
\<close>
haftmann@66808
   789
haftmann@66808
   790
simproc_setup cancel_div_mod_nat ("(m::nat) + n") =
haftmann@66808
   791
  \<open>K Cancel_Div_Mod_Nat.proc\<close>
haftmann@66808
   792
haftmann@66808
   793
lemma div_nat_eqI:
haftmann@66808
   794
  "m div n = q" if "n * q \<le> m" and "m < n * Suc q" for m n q :: nat
haftmann@66808
   795
  by (rule div_eqI [of _ "m - n * q"]) (use that in \<open>simp_all add: algebra_simps\<close>)
haftmann@66808
   796
haftmann@66808
   797
lemma mod_nat_eqI:
haftmann@66808
   798
  "m mod n = r" if "r < n" and "r \<le> m" and "n dvd m - r" for m n r :: nat
haftmann@66808
   799
  by (rule mod_eqI [of _ _ "(m - r) div n"]) (use that in \<open>simp_all add: algebra_simps\<close>)
haftmann@66808
   800
haftmann@66808
   801
lemma div_mult_self_is_m [simp]:
haftmann@66808
   802
  "m * n div n = m" if "n > 0" for m n :: nat
haftmann@66808
   803
  using that by simp
haftmann@66808
   804
haftmann@66808
   805
lemma div_mult_self1_is_m [simp]:
haftmann@66808
   806
  "n * m div n = m" if "n > 0" for m n :: nat
haftmann@66808
   807
  using that by simp
haftmann@66808
   808
haftmann@66808
   809
lemma mod_less_divisor [simp]:
haftmann@66808
   810
  "m mod n < n" if "n > 0" for m n :: nat
haftmann@66808
   811
  using mod_size_less [of n m] that by simp
haftmann@66808
   812
haftmann@66808
   813
lemma mod_le_divisor [simp]:
haftmann@66808
   814
  "m mod n \<le> n" if "n > 0" for m n :: nat
haftmann@66808
   815
  using that by (auto simp add: le_less)
haftmann@66808
   816
haftmann@66808
   817
lemma div_times_less_eq_dividend [simp]:
haftmann@66808
   818
  "m div n * n \<le> m" for m n :: nat
haftmann@66808
   819
  by (simp add: minus_mod_eq_div_mult [symmetric])
haftmann@66808
   820
haftmann@66808
   821
lemma times_div_less_eq_dividend [simp]:
haftmann@66808
   822
  "n * (m div n) \<le> m" for m n :: nat
haftmann@66808
   823
  using div_times_less_eq_dividend [of m n]
haftmann@66808
   824
  by (simp add: ac_simps)
haftmann@66808
   825
haftmann@66808
   826
lemma dividend_less_div_times:
haftmann@66808
   827
  "m < n + (m div n) * n" if "0 < n" for m n :: nat
haftmann@66808
   828
proof -
haftmann@66808
   829
  from that have "m mod n < n"
haftmann@66808
   830
    by simp
haftmann@66808
   831
  then show ?thesis
haftmann@66808
   832
    by (simp add: minus_mod_eq_div_mult [symmetric])
haftmann@66808
   833
qed
haftmann@66808
   834
haftmann@66808
   835
lemma dividend_less_times_div:
haftmann@66808
   836
  "m < n + n * (m div n)" if "0 < n" for m n :: nat
haftmann@66808
   837
  using dividend_less_div_times [of n m] that
haftmann@66808
   838
  by (simp add: ac_simps)
haftmann@66808
   839
haftmann@66808
   840
lemma mod_Suc_le_divisor [simp]:
haftmann@66808
   841
  "m mod Suc n \<le> n"
haftmann@66808
   842
  using mod_less_divisor [of "Suc n" m] by arith
haftmann@66808
   843
haftmann@66808
   844
lemma mod_less_eq_dividend [simp]:
haftmann@66808
   845
  "m mod n \<le> m" for m n :: nat
haftmann@66808
   846
proof (rule add_leD2)
haftmann@66808
   847
  from div_mult_mod_eq have "m div n * n + m mod n = m" .
haftmann@66808
   848
  then show "m div n * n + m mod n \<le> m" by auto
haftmann@66808
   849
qed
haftmann@66808
   850
haftmann@66808
   851
lemma
haftmann@66808
   852
  div_less [simp]: "m div n = 0"
haftmann@66808
   853
  and mod_less [simp]: "m mod n = m"
haftmann@66808
   854
  if "m < n" for m n :: nat
haftmann@66808
   855
  using that by (auto intro: div_eqI mod_eqI) 
haftmann@66808
   856
haftmann@66808
   857
lemma le_div_geq:
haftmann@66808
   858
  "m div n = Suc ((m - n) div n)" if "0 < n" and "n \<le> m" for m n :: nat
haftmann@66808
   859
proof -
haftmann@66808
   860
  from \<open>n \<le> m\<close> obtain q where "m = n + q"
haftmann@66808
   861
    by (auto simp add: le_iff_add)
haftmann@66808
   862
  with \<open>0 < n\<close> show ?thesis
haftmann@66808
   863
    by (simp add: div_add_self1)
haftmann@66808
   864
qed
haftmann@66808
   865
haftmann@66808
   866
lemma le_mod_geq:
haftmann@66808
   867
  "m mod n = (m - n) mod n" if "n \<le> m" for m n :: nat
haftmann@66808
   868
proof -
haftmann@66808
   869
  from \<open>n \<le> m\<close> obtain q where "m = n + q"
haftmann@66808
   870
    by (auto simp add: le_iff_add)
haftmann@66808
   871
  then show ?thesis
haftmann@66808
   872
    by simp
haftmann@66808
   873
qed
haftmann@66808
   874
haftmann@66808
   875
lemma div_if:
haftmann@66808
   876
  "m div n = (if m < n \<or> n = 0 then 0 else Suc ((m - n) div n))"
haftmann@66808
   877
  by (simp add: le_div_geq)
haftmann@66808
   878
haftmann@66808
   879
lemma mod_if:
haftmann@66808
   880
  "m mod n = (if m < n then m else (m - n) mod n)" for m n :: nat
haftmann@66808
   881
  by (simp add: le_mod_geq)
haftmann@66808
   882
haftmann@66808
   883
lemma div_eq_0_iff:
haftmann@66808
   884
  "m div n = 0 \<longleftrightarrow> m < n \<or> n = 0" for m n :: nat
haftmann@66808
   885
  by (simp add: div_if)
haftmann@66808
   886
haftmann@66808
   887
lemma div_greater_zero_iff:
haftmann@66808
   888
  "m div n > 0 \<longleftrightarrow> n \<le> m \<and> n > 0" for m n :: nat
haftmann@66808
   889
  using div_eq_0_iff [of m n] by auto
haftmann@66808
   890
haftmann@66808
   891
lemma mod_greater_zero_iff_not_dvd:
haftmann@66808
   892
  "m mod n > 0 \<longleftrightarrow> \<not> n dvd m" for m n :: nat
haftmann@66808
   893
  by (simp add: dvd_eq_mod_eq_0)
haftmann@66808
   894
haftmann@66808
   895
lemma div_by_Suc_0 [simp]:
haftmann@66808
   896
  "m div Suc 0 = m"
haftmann@66808
   897
  using div_by_1 [of m] by simp
haftmann@66808
   898
haftmann@66808
   899
lemma mod_by_Suc_0 [simp]:
haftmann@66808
   900
  "m mod Suc 0 = 0"
haftmann@66808
   901
  using mod_by_1 [of m] by simp
haftmann@66808
   902
haftmann@66808
   903
lemma div2_Suc_Suc [simp]:
haftmann@66808
   904
  "Suc (Suc m) div 2 = Suc (m div 2)"
haftmann@66808
   905
  by (simp add: numeral_2_eq_2 le_div_geq)
haftmann@66808
   906
haftmann@66808
   907
lemma Suc_n_div_2_gt_zero [simp]:
haftmann@66808
   908
  "0 < Suc n div 2" if "n > 0" for n :: nat
haftmann@66808
   909
  using that by (cases n) simp_all
haftmann@66808
   910
haftmann@66808
   911
lemma div_2_gt_zero [simp]:
haftmann@66808
   912
  "0 < n div 2" if "Suc 0 < n" for n :: nat
haftmann@66808
   913
  using that Suc_n_div_2_gt_zero [of "n - 1"] by simp
haftmann@66808
   914
haftmann@66808
   915
lemma mod2_Suc_Suc [simp]:
haftmann@66808
   916
  "Suc (Suc m) mod 2 = m mod 2"
haftmann@66808
   917
  by (simp add: numeral_2_eq_2 le_mod_geq)
haftmann@66808
   918
haftmann@66808
   919
lemma add_self_div_2 [simp]:
haftmann@66808
   920
  "(m + m) div 2 = m" for m :: nat
haftmann@66808
   921
  by (simp add: mult_2 [symmetric])
haftmann@66808
   922
haftmann@66808
   923
lemma add_self_mod_2 [simp]:
haftmann@66808
   924
  "(m + m) mod 2 = 0" for m :: nat
haftmann@66808
   925
  by (simp add: mult_2 [symmetric])
haftmann@66808
   926
haftmann@66808
   927
lemma mod2_gr_0 [simp]:
haftmann@66808
   928
  "0 < m mod 2 \<longleftrightarrow> m mod 2 = 1" for m :: nat
haftmann@66808
   929
proof -
haftmann@66808
   930
  have "m mod 2 < 2"
haftmann@66808
   931
    by (rule mod_less_divisor) simp
haftmann@66808
   932
  then have "m mod 2 = 0 \<or> m mod 2 = 1"
haftmann@66808
   933
    by arith
haftmann@66808
   934
  then show ?thesis
haftmann@66808
   935
    by auto     
haftmann@66808
   936
qed
haftmann@66808
   937
haftmann@66808
   938
lemma mod_Suc_eq [mod_simps]:
haftmann@66808
   939
  "Suc (m mod n) mod n = Suc m mod n"
haftmann@66808
   940
proof -
haftmann@66808
   941
  have "(m mod n + 1) mod n = (m + 1) mod n"
haftmann@66808
   942
    by (simp only: mod_simps)
haftmann@66808
   943
  then show ?thesis
haftmann@66808
   944
    by simp
haftmann@66808
   945
qed
haftmann@66808
   946
haftmann@66808
   947
lemma mod_Suc_Suc_eq [mod_simps]:
haftmann@66808
   948
  "Suc (Suc (m mod n)) mod n = Suc (Suc m) mod n"
haftmann@66808
   949
proof -
haftmann@66808
   950
  have "(m mod n + 2) mod n = (m + 2) mod n"
haftmann@66808
   951
    by (simp only: mod_simps)
haftmann@66808
   952
  then show ?thesis
haftmann@66808
   953
    by simp
haftmann@66808
   954
qed
haftmann@66808
   955
haftmann@66808
   956
lemma
haftmann@66808
   957
  Suc_mod_mult_self1 [simp]: "Suc (m + k * n) mod n = Suc m mod n"
haftmann@66808
   958
  and Suc_mod_mult_self2 [simp]: "Suc (m + n * k) mod n = Suc m mod n"
haftmann@66808
   959
  and Suc_mod_mult_self3 [simp]: "Suc (k * n + m) mod n = Suc m mod n"
haftmann@66808
   960
  and Suc_mod_mult_self4 [simp]: "Suc (n * k + m) mod n = Suc m mod n"
haftmann@66808
   961
  by (subst mod_Suc_eq [symmetric], simp add: mod_simps)+
haftmann@66808
   962
haftmann@66808
   963
lemma div_mult1_eq: -- \<open>TODO: Generalization candidate\<close>
haftmann@66808
   964
  "(a * b) div c = a * (b div c) + a * (b mod c) div c" for a b c :: nat
haftmann@66808
   965
  apply (cases "c = 0")
haftmann@66808
   966
   apply simp
haftmann@66808
   967
  apply (rule div_eqI [of _ "(a * (b mod c)) mod c"])
haftmann@66808
   968
     apply (auto simp add: algebra_simps distrib_left [symmetric])
haftmann@66808
   969
  done
haftmann@66808
   970
haftmann@66808
   971
lemma div_add1_eq: -- \<open>NOT suitable for rewriting: the RHS has an instance of the LHS\<close>
haftmann@66808
   972
   -- \<open>TODO: Generalization candidate\<close>
haftmann@66808
   973
  "(a + b) div c = a div c + b div c + ((a mod c + b mod c) div c)" for a b c :: nat
haftmann@66808
   974
  apply (cases "c = 0")
haftmann@66808
   975
   apply simp
haftmann@66808
   976
  apply (rule div_eqI [of _ "(a mod c + b mod c) mod c"])
haftmann@66808
   977
  apply (auto simp add: algebra_simps)
haftmann@66808
   978
  done
haftmann@66808
   979
haftmann@66808
   980
context
haftmann@66808
   981
  fixes m n q :: nat
haftmann@66808
   982
begin
haftmann@66808
   983
haftmann@66808
   984
private lemma eucl_rel_mult2:
haftmann@66808
   985
  "m mod n + n * (m div n mod q) < n * q"
haftmann@66808
   986
  if "n > 0" and "q > 0"
haftmann@66808
   987
proof -
haftmann@66808
   988
  from \<open>n > 0\<close> have "m mod n < n"
haftmann@66808
   989
    by (rule mod_less_divisor)
haftmann@66808
   990
  from \<open>q > 0\<close> have "m div n mod q < q"
haftmann@66808
   991
    by (rule mod_less_divisor)
haftmann@66808
   992
  then obtain s where "q = Suc (m div n mod q + s)"
haftmann@66808
   993
    by (blast dest: less_imp_Suc_add)
haftmann@66808
   994
  moreover have "m mod n + n * (m div n mod q) < n * Suc (m div n mod q + s)"
haftmann@66808
   995
    using \<open>m mod n < n\<close> by (simp add: add_mult_distrib2)
haftmann@66808
   996
  ultimately show ?thesis
haftmann@66808
   997
    by simp
haftmann@66808
   998
qed
haftmann@66808
   999
haftmann@66808
  1000
lemma div_mult2_eq:
haftmann@66808
  1001
  "m div (n * q) = (m div n) div q"
haftmann@66808
  1002
proof (cases "n = 0 \<or> q = 0")
haftmann@66808
  1003
  case True
haftmann@66808
  1004
  then show ?thesis
haftmann@66808
  1005
    by auto
haftmann@66808
  1006
next
haftmann@66808
  1007
  case False
haftmann@66808
  1008
  with eucl_rel_mult2 show ?thesis
haftmann@66808
  1009
    by (auto intro: div_eqI [of _ "n * (m div n mod q) + m mod n"]
haftmann@66808
  1010
      simp add: algebra_simps add_mult_distrib2 [symmetric])
haftmann@66808
  1011
qed
haftmann@66808
  1012
haftmann@66808
  1013
lemma mod_mult2_eq:
haftmann@66808
  1014
  "m mod (n * q) = n * (m div n mod q) + m mod n"
haftmann@66808
  1015
proof (cases "n = 0 \<or> q = 0")
haftmann@66808
  1016
  case True
haftmann@66808
  1017
  then show ?thesis
haftmann@66808
  1018
    by auto
haftmann@66808
  1019
next
haftmann@66808
  1020
  case False
haftmann@66808
  1021
  with eucl_rel_mult2 show ?thesis
haftmann@66808
  1022
    by (auto intro: mod_eqI [of _ _ "(m div n) div q"]
haftmann@66808
  1023
      simp add: algebra_simps add_mult_distrib2 [symmetric])
haftmann@66808
  1024
qed
haftmann@66808
  1025
haftmann@66808
  1026
end
haftmann@66808
  1027
haftmann@66808
  1028
lemma div_le_mono:
haftmann@66808
  1029
  "m div k \<le> n div k" if "m \<le> n" for m n k :: nat
haftmann@66808
  1030
proof -
haftmann@66808
  1031
  from that obtain q where "n = m + q"
haftmann@66808
  1032
    by (auto simp add: le_iff_add)
haftmann@66808
  1033
  then show ?thesis
haftmann@66808
  1034
    by (simp add: div_add1_eq [of m q k])
haftmann@66808
  1035
qed
haftmann@66808
  1036
haftmann@66808
  1037
text \<open>Antimonotonicity of @{const divide} in second argument\<close>
haftmann@66808
  1038
haftmann@66808
  1039
lemma div_le_mono2:
haftmann@66808
  1040
  "k div n \<le> k div m" if "0 < m" and "m \<le> n" for m n k :: nat
haftmann@66808
  1041
using that proof (induct k arbitrary: m rule: less_induct)
haftmann@66808
  1042
  case (less k)
haftmann@66808
  1043
  show ?case
haftmann@66808
  1044
  proof (cases "n \<le> k")
haftmann@66808
  1045
    case False
haftmann@66808
  1046
    then show ?thesis
haftmann@66808
  1047
      by simp
haftmann@66808
  1048
  next
haftmann@66808
  1049
    case True
haftmann@66808
  1050
    have "(k - n) div n \<le> (k - m) div n"
haftmann@66808
  1051
      using less.prems
haftmann@66808
  1052
      by (blast intro: div_le_mono diff_le_mono2)
haftmann@66808
  1053
    also have "\<dots> \<le> (k - m) div m"
haftmann@66808
  1054
      using \<open>n \<le> k\<close> less.prems less.hyps [of "k - m" m]
haftmann@66808
  1055
      by simp
haftmann@66808
  1056
    finally show ?thesis
haftmann@66808
  1057
      using \<open>n \<le> k\<close> less.prems
haftmann@66808
  1058
      by (simp add: le_div_geq)
haftmann@66808
  1059
  qed
haftmann@66808
  1060
qed
haftmann@66808
  1061
haftmann@66808
  1062
lemma div_le_dividend [simp]:
haftmann@66808
  1063
  "m div n \<le> m" for m n :: nat
haftmann@66808
  1064
  using div_le_mono2 [of 1 n m] by (cases "n = 0") simp_all
haftmann@66808
  1065
haftmann@66808
  1066
lemma div_less_dividend [simp]:
haftmann@66808
  1067
  "m div n < m" if "1 < n" and "0 < m" for m n :: nat
haftmann@66808
  1068
using that proof (induct m rule: less_induct)
haftmann@66808
  1069
  case (less m)
haftmann@66808
  1070
  show ?case
haftmann@66808
  1071
  proof (cases "n < m")
haftmann@66808
  1072
    case False
haftmann@66808
  1073
    with less show ?thesis
haftmann@66808
  1074
      by (cases "n = m") simp_all
haftmann@66808
  1075
  next
haftmann@66808
  1076
    case True
haftmann@66808
  1077
    then show ?thesis
haftmann@66808
  1078
      using less.hyps [of "m - n"] less.prems
haftmann@66808
  1079
      by (simp add: le_div_geq)
haftmann@66808
  1080
  qed
haftmann@66808
  1081
qed
haftmann@66808
  1082
haftmann@66808
  1083
lemma div_eq_dividend_iff:
haftmann@66808
  1084
  "m div n = m \<longleftrightarrow> n = 1" if "m > 0" for m n :: nat
haftmann@66808
  1085
proof
haftmann@66808
  1086
  assume "n = 1"
haftmann@66808
  1087
  then show "m div n = m"
haftmann@66808
  1088
    by simp
haftmann@66808
  1089
next
haftmann@66808
  1090
  assume P: "m div n = m"
haftmann@66808
  1091
  show "n = 1"
haftmann@66808
  1092
  proof (rule ccontr)
haftmann@66808
  1093
    have "n \<noteq> 0"
haftmann@66808
  1094
      by (rule ccontr) (use that P in auto)
haftmann@66808
  1095
    moreover assume "n \<noteq> 1"
haftmann@66808
  1096
    ultimately have "n > 1"
haftmann@66808
  1097
      by simp
haftmann@66808
  1098
    with that have "m div n < m"
haftmann@66808
  1099
      by simp
haftmann@66808
  1100
    with P show False
haftmann@66808
  1101
      by simp
haftmann@66808
  1102
  qed
haftmann@66808
  1103
qed
haftmann@66808
  1104
haftmann@66808
  1105
lemma less_mult_imp_div_less:
haftmann@66808
  1106
  "m div n < i" if "m < i * n" for m n i :: nat
haftmann@66808
  1107
proof -
haftmann@66808
  1108
  from that have "i * n > 0"
haftmann@66808
  1109
    by (cases "i * n = 0") simp_all
haftmann@66808
  1110
  then have "i > 0" and "n > 0"
haftmann@66808
  1111
    by simp_all
haftmann@66808
  1112
  have "m div n * n \<le> m"
haftmann@66808
  1113
    by simp
haftmann@66808
  1114
  then have "m div n * n < i * n"
haftmann@66808
  1115
    using that by (rule le_less_trans)
haftmann@66808
  1116
  with \<open>n > 0\<close> show ?thesis
haftmann@66808
  1117
    by simp
haftmann@66808
  1118
qed
haftmann@66808
  1119
haftmann@66808
  1120
text \<open>A fact for the mutilated chess board\<close>
haftmann@66808
  1121
haftmann@66808
  1122
lemma mod_Suc:
haftmann@66808
  1123
  "Suc m mod n = (if Suc (m mod n) = n then 0 else Suc (m mod n))" (is "_ = ?rhs")
haftmann@66808
  1124
proof (cases "n = 0")
haftmann@66808
  1125
  case True
haftmann@66808
  1126
  then show ?thesis
haftmann@66808
  1127
    by simp
haftmann@66808
  1128
next
haftmann@66808
  1129
  case False
haftmann@66808
  1130
  have "Suc m mod n = Suc (m mod n) mod n"
haftmann@66808
  1131
    by (simp add: mod_simps)
haftmann@66808
  1132
  also have "\<dots> = ?rhs"
haftmann@66808
  1133
    using False by (auto intro!: mod_nat_eqI intro: neq_le_trans simp add: Suc_le_eq)
haftmann@66808
  1134
  finally show ?thesis .
haftmann@66808
  1135
qed
haftmann@66808
  1136
haftmann@66808
  1137
lemma Suc_times_mod_eq:
haftmann@66808
  1138
  "Suc (m * n) mod m = 1" if "Suc 0 < m"
haftmann@66808
  1139
  using that by (simp add: mod_Suc)
haftmann@66808
  1140
haftmann@66808
  1141
lemma Suc_times_numeral_mod_eq [simp]:
haftmann@66808
  1142
  "Suc (numeral k * n) mod numeral k = 1" if "numeral k \<noteq> (1::nat)"
haftmann@66808
  1143
  by (rule Suc_times_mod_eq) (use that in simp)
haftmann@66808
  1144
haftmann@66808
  1145
lemma Suc_div_le_mono [simp]:
haftmann@66808
  1146
  "m div n \<le> Suc m div n"
haftmann@66808
  1147
  by (simp add: div_le_mono)
haftmann@66808
  1148
haftmann@66808
  1149
text \<open>These lemmas collapse some needless occurrences of Suc:
haftmann@66808
  1150
  at least three Sucs, since two and fewer are rewritten back to Suc again!
haftmann@66808
  1151
  We already have some rules to simplify operands smaller than 3.\<close>
haftmann@66808
  1152
haftmann@66808
  1153
lemma div_Suc_eq_div_add3 [simp]:
haftmann@66808
  1154
  "m div Suc (Suc (Suc n)) = m div (3 + n)"
haftmann@66808
  1155
  by (simp add: Suc3_eq_add_3)
haftmann@66808
  1156
haftmann@66808
  1157
lemma mod_Suc_eq_mod_add3 [simp]:
haftmann@66808
  1158
  "m mod Suc (Suc (Suc n)) = m mod (3 + n)"
haftmann@66808
  1159
  by (simp add: Suc3_eq_add_3)
haftmann@66808
  1160
haftmann@66808
  1161
lemma Suc_div_eq_add3_div:
haftmann@66808
  1162
  "Suc (Suc (Suc m)) div n = (3 + m) div n"
haftmann@66808
  1163
  by (simp add: Suc3_eq_add_3)
haftmann@66808
  1164
haftmann@66808
  1165
lemma Suc_mod_eq_add3_mod:
haftmann@66808
  1166
  "Suc (Suc (Suc m)) mod n = (3 + m) mod n"
haftmann@66808
  1167
  by (simp add: Suc3_eq_add_3)
haftmann@66808
  1168
haftmann@66808
  1169
lemmas Suc_div_eq_add3_div_numeral [simp] =
haftmann@66808
  1170
  Suc_div_eq_add3_div [of _ "numeral v"] for v
haftmann@66808
  1171
haftmann@66808
  1172
lemmas Suc_mod_eq_add3_mod_numeral [simp] =
haftmann@66808
  1173
  Suc_mod_eq_add3_mod [of _ "numeral v"] for v
haftmann@66808
  1174
haftmann@66808
  1175
lemma (in field_char_0) of_nat_div:
haftmann@66808
  1176
  "of_nat (m div n) = ((of_nat m - of_nat (m mod n)) / of_nat n)"
haftmann@66808
  1177
proof -
haftmann@66808
  1178
  have "of_nat (m div n) = ((of_nat (m div n * n + m mod n) - of_nat (m mod n)) / of_nat n :: 'a)"
haftmann@66808
  1179
    unfolding of_nat_add by (cases "n = 0") simp_all
haftmann@66808
  1180
  then show ?thesis
haftmann@66808
  1181
    by simp
haftmann@66808
  1182
qed
haftmann@66808
  1183
haftmann@66808
  1184
text \<open>An ``induction'' law for modulus arithmetic.\<close>
haftmann@66808
  1185
haftmann@66808
  1186
lemma mod_induct [consumes 3, case_names step]:
haftmann@66808
  1187
  "P m" if "P n" and "n < p" and "m < p"
haftmann@66808
  1188
    and step: "\<And>n. n < p \<Longrightarrow> P n \<Longrightarrow> P (Suc n mod p)"
haftmann@66808
  1189
using \<open>m < p\<close> proof (induct m)
haftmann@66808
  1190
  case 0
haftmann@66808
  1191
  show ?case
haftmann@66808
  1192
  proof (rule ccontr)
haftmann@66808
  1193
    assume "\<not> P 0"
haftmann@66808
  1194
    from \<open>n < p\<close> have "0 < p"
haftmann@66808
  1195
      by simp
haftmann@66808
  1196
    from \<open>n < p\<close> obtain m where "0 < m" and "p = n + m"
haftmann@66808
  1197
      by (blast dest: less_imp_add_positive)
haftmann@66808
  1198
    with \<open>P n\<close> have "P (p - m)"
haftmann@66808
  1199
      by simp
haftmann@66808
  1200
    moreover have "\<not> P (p - m)"
haftmann@66808
  1201
    using \<open>0 < m\<close> proof (induct m)
haftmann@66808
  1202
      case 0
haftmann@66808
  1203
      then show ?case
haftmann@66808
  1204
        by simp
haftmann@66808
  1205
    next
haftmann@66808
  1206
      case (Suc m)
haftmann@66808
  1207
      show ?case
haftmann@66808
  1208
      proof
haftmann@66808
  1209
        assume P: "P (p - Suc m)"
haftmann@66808
  1210
        with \<open>\<not> P 0\<close> have "Suc m < p"
haftmann@66808
  1211
          by (auto intro: ccontr) 
haftmann@66808
  1212
        then have "Suc (p - Suc m) = p - m"
haftmann@66808
  1213
          by arith
haftmann@66808
  1214
        moreover from \<open>0 < p\<close> have "p - Suc m < p"
haftmann@66808
  1215
          by arith
haftmann@66808
  1216
        with P step have "P ((Suc (p - Suc m)) mod p)"
haftmann@66808
  1217
          by blast
haftmann@66808
  1218
        ultimately show False
haftmann@66808
  1219
          using \<open>\<not> P 0\<close> Suc.hyps by (cases "m = 0") simp_all
haftmann@66808
  1220
      qed
haftmann@66808
  1221
    qed
haftmann@66808
  1222
    ultimately show False
haftmann@66808
  1223
      by blast
haftmann@66808
  1224
  qed
haftmann@66808
  1225
next
haftmann@66808
  1226
  case (Suc m)
haftmann@66808
  1227
  then have "m < p" and mod: "Suc m mod p = Suc m"
haftmann@66808
  1228
    by simp_all
haftmann@66808
  1229
  from \<open>m < p\<close> have "P m"
haftmann@66808
  1230
    by (rule Suc.hyps)
haftmann@66808
  1231
  with \<open>m < p\<close> have "P (Suc m mod p)"
haftmann@66808
  1232
    by (rule step)
haftmann@66808
  1233
  with mod show ?case
haftmann@66808
  1234
    by simp
haftmann@66808
  1235
qed
haftmann@66808
  1236
haftmann@66808
  1237
lemma split_div:
haftmann@66808
  1238
  "P (m div n) \<longleftrightarrow> (n = 0 \<longrightarrow> P 0) \<and> (n \<noteq> 0 \<longrightarrow>
haftmann@66808
  1239
     (\<forall>i j. j < n \<longrightarrow> m = n * i + j \<longrightarrow> P i))"
haftmann@66808
  1240
     (is "?P = ?Q") for m n :: nat
haftmann@66808
  1241
proof (cases "n = 0")
haftmann@66808
  1242
  case True
haftmann@66808
  1243
  then show ?thesis
haftmann@66808
  1244
    by simp
haftmann@66808
  1245
next
haftmann@66808
  1246
  case False
haftmann@66808
  1247
  show ?thesis
haftmann@66808
  1248
  proof
haftmann@66808
  1249
    assume ?P
haftmann@66808
  1250
    with False show ?Q
haftmann@66808
  1251
      by auto
haftmann@66808
  1252
  next
haftmann@66808
  1253
    assume ?Q
haftmann@66808
  1254
    with False have *: "\<And>i j. j < n \<Longrightarrow> m = n * i + j \<Longrightarrow> P i"
haftmann@66808
  1255
      by simp
haftmann@66808
  1256
    with False show ?P
haftmann@66808
  1257
      by (auto intro: * [of "m mod n"])
haftmann@66808
  1258
  qed
haftmann@66808
  1259
qed
haftmann@66808
  1260
haftmann@66808
  1261
lemma split_div':
haftmann@66808
  1262
  "P (m div n) \<longleftrightarrow> n = 0 \<and> P 0 \<or> (\<exists>q. (n * q \<le> m \<and> m < n * Suc q) \<and> P q)"
haftmann@66808
  1263
proof (cases "n = 0")
haftmann@66808
  1264
  case True
haftmann@66808
  1265
  then show ?thesis
haftmann@66808
  1266
    by simp
haftmann@66808
  1267
next
haftmann@66808
  1268
  case False
haftmann@66808
  1269
  then have "n * q \<le> m \<and> m < n * Suc q \<longleftrightarrow> m div n = q" for q
haftmann@66808
  1270
    by (auto intro: div_nat_eqI dividend_less_times_div)
haftmann@66808
  1271
  then show ?thesis
haftmann@66808
  1272
    by auto
haftmann@66808
  1273
qed
haftmann@66808
  1274
haftmann@66808
  1275
lemma split_mod:
haftmann@66808
  1276
  "P (m mod n) \<longleftrightarrow> (n = 0 \<longrightarrow> P m) \<and> (n \<noteq> 0 \<longrightarrow>
haftmann@66808
  1277
     (\<forall>i j. j < n \<longrightarrow> m = n * i + j \<longrightarrow> P j))"
haftmann@66808
  1278
     (is "?P \<longleftrightarrow> ?Q") for m n :: nat
haftmann@66808
  1279
proof (cases "n = 0")
haftmann@66808
  1280
  case True
haftmann@66808
  1281
  then show ?thesis
haftmann@66808
  1282
    by simp
haftmann@66808
  1283
next
haftmann@66808
  1284
  case False
haftmann@66808
  1285
  show ?thesis
haftmann@66808
  1286
  proof
haftmann@66808
  1287
    assume ?P
haftmann@66808
  1288
    with False show ?Q
haftmann@66808
  1289
      by auto
haftmann@66808
  1290
  next
haftmann@66808
  1291
    assume ?Q
haftmann@66808
  1292
    with False have *: "\<And>i j. j < n \<Longrightarrow> m = n * i + j \<Longrightarrow> P j"
haftmann@66808
  1293
      by simp
haftmann@66808
  1294
    with False show ?P
haftmann@66808
  1295
      by (auto intro: * [of _ "m div n"])
haftmann@66808
  1296
  qed
haftmann@66808
  1297
qed
haftmann@66808
  1298
haftmann@66808
  1299
haftmann@66808
  1300
subsection \<open>Code generation\<close>
haftmann@66808
  1301
haftmann@66808
  1302
code_identifier
haftmann@66808
  1303
  code_module Euclidean_Division \<rightharpoonup> (SML) Arith and (OCaml) Arith and (Haskell) Arith
haftmann@66808
  1304
haftmann@66808
  1305
end