src/HOL/Rings.thy
author haftmann
Thu May 06 23:11:56 2010 +0200 (2010-05-06)
changeset 36719 d396f6f63d94
parent 36622 e393a91f86df
child 36821 9207505d1ee5
permissions -rw-r--r--
moved some lemmas from Groebner_Basis here
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(*  Title:      HOL/Rings.thy
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    Author:     Gertrud Bauer
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    Author:     Steven Obua
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    Author:     Tobias Nipkow
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    Author:     Lawrence C Paulson
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    Author:     Markus Wenzel
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    Author:     Jeremy Avigad
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*)
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header {* Rings *}
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theory Rings
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imports Groups
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begin
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class semiring = ab_semigroup_add + semigroup_mult +
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  assumes left_distrib[algebra_simps, field_simps]: "(a + b) * c = a * c + b * c"
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  assumes right_distrib[algebra_simps, field_simps]: "a * (b + c) = a * b + a * c"
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begin
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text{*For the @{text combine_numerals} simproc*}
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lemma combine_common_factor:
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  "a * e + (b * e + c) = (a + b) * e + c"
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by (simp add: left_distrib add_ac)
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end
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class mult_zero = times + zero +
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  assumes mult_zero_left [simp]: "0 * a = 0"
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  assumes mult_zero_right [simp]: "a * 0 = 0"
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class semiring_0 = semiring + comm_monoid_add + mult_zero
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class semiring_0_cancel = semiring + cancel_comm_monoid_add
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begin
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subclass semiring_0
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proof
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  fix a :: 'a
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  have "0 * a + 0 * a = 0 * a + 0" by (simp add: left_distrib [symmetric])
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  thus "0 * a = 0" by (simp only: add_left_cancel)
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next
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  fix a :: 'a
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  have "a * 0 + a * 0 = a * 0 + 0" by (simp add: right_distrib [symmetric])
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  thus "a * 0 = 0" by (simp only: add_left_cancel)
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qed
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end
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class comm_semiring = ab_semigroup_add + ab_semigroup_mult +
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  assumes distrib: "(a + b) * c = a * c + b * c"
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begin
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subclass semiring
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proof
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  fix a b c :: 'a
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  show "(a + b) * c = a * c + b * c" by (simp add: distrib)
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  have "a * (b + c) = (b + c) * a" by (simp add: mult_ac)
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  also have "... = b * a + c * a" by (simp only: distrib)
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  also have "... = a * b + a * c" by (simp add: mult_ac)
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  finally show "a * (b + c) = a * b + a * c" by blast
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qed
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end
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class comm_semiring_0 = comm_semiring + comm_monoid_add + mult_zero
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begin
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subclass semiring_0 ..
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end
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class comm_semiring_0_cancel = comm_semiring + cancel_comm_monoid_add
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begin
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subclass semiring_0_cancel ..
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subclass comm_semiring_0 ..
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end
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class zero_neq_one = zero + one +
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  assumes zero_neq_one [simp]: "0 \<noteq> 1"
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begin
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lemma one_neq_zero [simp]: "1 \<noteq> 0"
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by (rule not_sym) (rule zero_neq_one)
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end
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class semiring_1 = zero_neq_one + semiring_0 + monoid_mult
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text {* Abstract divisibility *}
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class dvd = times
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begin
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definition dvd :: "'a \<Rightarrow> 'a \<Rightarrow> bool" (infixl "dvd" 50) where
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  [code del]: "b dvd a \<longleftrightarrow> (\<exists>k. a = b * k)"
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lemma dvdI [intro?]: "a = b * k \<Longrightarrow> b dvd a"
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  unfolding dvd_def ..
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lemma dvdE [elim?]: "b dvd a \<Longrightarrow> (\<And>k. a = b * k \<Longrightarrow> P) \<Longrightarrow> P"
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  unfolding dvd_def by blast 
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end
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class comm_semiring_1 = zero_neq_one + comm_semiring_0 + comm_monoid_mult + dvd
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  (*previously almost_semiring*)
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begin
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subclass semiring_1 ..
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lemma dvd_refl[simp]: "a dvd a"
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proof
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  show "a = a * 1" by simp
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qed
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lemma dvd_trans:
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  assumes "a dvd b" and "b dvd c"
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  shows "a dvd c"
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proof -
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  from assms obtain v where "b = a * v" by (auto elim!: dvdE)
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  moreover from assms obtain w where "c = b * w" by (auto elim!: dvdE)
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  ultimately have "c = a * (v * w)" by (simp add: mult_assoc)
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  then show ?thesis ..
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qed
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lemma dvd_0_left_iff [no_atp, simp]: "0 dvd a \<longleftrightarrow> a = 0"
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by (auto intro: dvd_refl elim!: dvdE)
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lemma dvd_0_right [iff]: "a dvd 0"
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proof
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  show "0 = a * 0" by simp
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qed
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lemma one_dvd [simp]: "1 dvd a"
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by (auto intro!: dvdI)
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lemma dvd_mult[simp]: "a dvd c \<Longrightarrow> a dvd (b * c)"
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by (auto intro!: mult_left_commute dvdI elim!: dvdE)
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lemma dvd_mult2[simp]: "a dvd b \<Longrightarrow> a dvd (b * c)"
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  apply (subst mult_commute)
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  apply (erule dvd_mult)
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  done
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lemma dvd_triv_right [simp]: "a dvd b * a"
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by (rule dvd_mult) (rule dvd_refl)
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lemma dvd_triv_left [simp]: "a dvd a * b"
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by (rule dvd_mult2) (rule dvd_refl)
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lemma mult_dvd_mono:
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  assumes "a dvd b"
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    and "c dvd d"
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  shows "a * c dvd b * d"
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proof -
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  from `a dvd b` obtain b' where "b = a * b'" ..
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  moreover from `c dvd d` obtain d' where "d = c * d'" ..
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  ultimately have "b * d = (a * c) * (b' * d')" by (simp add: mult_ac)
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  then show ?thesis ..
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qed
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lemma dvd_mult_left: "a * b dvd c \<Longrightarrow> a dvd c"
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by (simp add: dvd_def mult_assoc, blast)
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lemma dvd_mult_right: "a * b dvd c \<Longrightarrow> b dvd c"
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  unfolding mult_ac [of a] by (rule dvd_mult_left)
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lemma dvd_0_left: "0 dvd a \<Longrightarrow> a = 0"
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by simp
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lemma dvd_add[simp]:
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  assumes "a dvd b" and "a dvd c" shows "a dvd (b + c)"
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proof -
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  from `a dvd b` obtain b' where "b = a * b'" ..
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  moreover from `a dvd c` obtain c' where "c = a * c'" ..
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  ultimately have "b + c = a * (b' + c')" by (simp add: right_distrib)
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  then show ?thesis ..
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qed
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end
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class no_zero_divisors = zero + times +
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  assumes no_zero_divisors: "a \<noteq> 0 \<Longrightarrow> b \<noteq> 0 \<Longrightarrow> a * b \<noteq> 0"
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begin
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lemma divisors_zero:
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  assumes "a * b = 0"
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  shows "a = 0 \<or> b = 0"
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proof (rule classical)
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  assume "\<not> (a = 0 \<or> b = 0)"
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  then have "a \<noteq> 0" and "b \<noteq> 0" by auto
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  with no_zero_divisors have "a * b \<noteq> 0" by blast
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  with assms show ?thesis by simp
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qed
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end
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class semiring_1_cancel = semiring + cancel_comm_monoid_add
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  + zero_neq_one + monoid_mult
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begin
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subclass semiring_0_cancel ..
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subclass semiring_1 ..
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end
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class comm_semiring_1_cancel = comm_semiring + cancel_comm_monoid_add
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  + zero_neq_one + comm_monoid_mult
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begin
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subclass semiring_1_cancel ..
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subclass comm_semiring_0_cancel ..
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subclass comm_semiring_1 ..
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end
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class ring = semiring + ab_group_add
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begin
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subclass semiring_0_cancel ..
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text {* Distribution rules *}
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lemma minus_mult_left: "- (a * b) = - a * b"
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by (rule minus_unique) (simp add: left_distrib [symmetric]) 
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lemma minus_mult_right: "- (a * b) = a * - b"
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by (rule minus_unique) (simp add: right_distrib [symmetric]) 
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text{*Extract signs from products*}
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lemmas mult_minus_left [simp, no_atp] = minus_mult_left [symmetric]
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lemmas mult_minus_right [simp,no_atp] = minus_mult_right [symmetric]
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lemma minus_mult_minus [simp]: "- a * - b = a * b"
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by simp
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lemma minus_mult_commute: "- a * b = a * - b"
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by simp
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lemma right_diff_distrib[algebra_simps, field_simps]: "a * (b - c) = a * b - a * c"
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by (simp add: right_distrib diff_minus)
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lemma left_diff_distrib[algebra_simps, field_simps]: "(a - b) * c = a * c - b * c"
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by (simp add: left_distrib diff_minus)
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lemmas ring_distribs[no_atp] =
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  right_distrib left_distrib left_diff_distrib right_diff_distrib
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lemma eq_add_iff1:
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  "a * e + c = b * e + d \<longleftrightarrow> (a - b) * e + c = d"
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by (simp add: algebra_simps)
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lemma eq_add_iff2:
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  "a * e + c = b * e + d \<longleftrightarrow> c = (b - a) * e + d"
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by (simp add: algebra_simps)
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end
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lemmas ring_distribs[no_atp] =
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  right_distrib left_distrib left_diff_distrib right_diff_distrib
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class comm_ring = comm_semiring + ab_group_add
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begin
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subclass ring ..
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subclass comm_semiring_0_cancel ..
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end
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class ring_1 = ring + zero_neq_one + monoid_mult
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begin
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subclass semiring_1_cancel ..
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end
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class comm_ring_1 = comm_ring + zero_neq_one + comm_monoid_mult
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  (*previously ring*)
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begin
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subclass ring_1 ..
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subclass comm_semiring_1_cancel ..
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lemma dvd_minus_iff [simp]: "x dvd - y \<longleftrightarrow> x dvd y"
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proof
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  assume "x dvd - y"
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  then have "x dvd - 1 * - y" by (rule dvd_mult)
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  then show "x dvd y" by simp
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next
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  assume "x dvd y"
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  then have "x dvd - 1 * y" by (rule dvd_mult)
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  then show "x dvd - y" by simp
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qed
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lemma minus_dvd_iff [simp]: "- x dvd y \<longleftrightarrow> x dvd y"
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proof
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  assume "- x dvd y"
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  then obtain k where "y = - x * k" ..
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  then have "y = x * - k" by simp
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  then show "x dvd y" ..
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next
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  assume "x dvd y"
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  then obtain k where "y = x * k" ..
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  then have "y = - x * - k" by simp
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  then show "- x dvd y" ..
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qed
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lemma dvd_diff[simp]: "x dvd y \<Longrightarrow> x dvd z \<Longrightarrow> x dvd (y - z)"
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by (simp only: diff_minus dvd_add dvd_minus_iff)
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end
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class ring_no_zero_divisors = ring + no_zero_divisors
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begin
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lemma mult_eq_0_iff [simp]:
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  shows "a * b = 0 \<longleftrightarrow> (a = 0 \<or> b = 0)"
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proof (cases "a = 0 \<or> b = 0")
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  case False then have "a \<noteq> 0" and "b \<noteq> 0" by auto
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    then show ?thesis using no_zero_divisors by simp
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next
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  case True then show ?thesis by auto
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qed
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text{*Cancellation of equalities with a common factor*}
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lemma mult_cancel_right [simp, no_atp]:
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  "a * c = b * c \<longleftrightarrow> c = 0 \<or> a = b"
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proof -
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  have "(a * c = b * c) = ((a - b) * c = 0)"
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    by (simp add: algebra_simps)
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  thus ?thesis by (simp add: disj_commute)
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qed
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lemma mult_cancel_left [simp, no_atp]:
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  "c * a = c * b \<longleftrightarrow> c = 0 \<or> a = b"
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proof -
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  have "(c * a = c * b) = (c * (a - b) = 0)"
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    by (simp add: algebra_simps)
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  thus ?thesis by simp
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qed
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end
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class ring_1_no_zero_divisors = ring_1 + ring_no_zero_divisors
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begin
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lemma mult_cancel_right1 [simp]:
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  "c = b * c \<longleftrightarrow> c = 0 \<or> b = 1"
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by (insert mult_cancel_right [of 1 c b], force)
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lemma mult_cancel_right2 [simp]:
haftmann@26274
   357
  "a * c = c \<longleftrightarrow> c = 0 \<or> a = 1"
nipkow@29667
   358
by (insert mult_cancel_right [of a c 1], simp)
haftmann@26274
   359
 
haftmann@26274
   360
lemma mult_cancel_left1 [simp]:
haftmann@26274
   361
  "c = c * b \<longleftrightarrow> c = 0 \<or> b = 1"
nipkow@29667
   362
by (insert mult_cancel_left [of c 1 b], force)
haftmann@26274
   363
haftmann@26274
   364
lemma mult_cancel_left2 [simp]:
haftmann@26274
   365
  "c * a = c \<longleftrightarrow> c = 0 \<or> a = 1"
nipkow@29667
   366
by (insert mult_cancel_left [of c a 1], simp)
haftmann@26274
   367
haftmann@26274
   368
end
huffman@22990
   369
haftmann@22390
   370
class idom = comm_ring_1 + no_zero_divisors
haftmann@25186
   371
begin
paulson@14421
   372
huffman@27516
   373
subclass ring_1_no_zero_divisors ..
huffman@22990
   374
huffman@29915
   375
lemma square_eq_iff: "a * a = b * b \<longleftrightarrow> (a = b \<or> a = - b)"
huffman@29915
   376
proof
huffman@29915
   377
  assume "a * a = b * b"
huffman@29915
   378
  then have "(a - b) * (a + b) = 0"
huffman@29915
   379
    by (simp add: algebra_simps)
huffman@29915
   380
  then show "a = b \<or> a = - b"
huffman@35216
   381
    by (simp add: eq_neg_iff_add_eq_0)
huffman@29915
   382
next
huffman@29915
   383
  assume "a = b \<or> a = - b"
huffman@29915
   384
  then show "a * a = b * b" by auto
huffman@29915
   385
qed
huffman@29915
   386
huffman@29981
   387
lemma dvd_mult_cancel_right [simp]:
huffman@29981
   388
  "a * c dvd b * c \<longleftrightarrow> c = 0 \<or> a dvd b"
huffman@29981
   389
proof -
huffman@29981
   390
  have "a * c dvd b * c \<longleftrightarrow> (\<exists>k. b * c = (a * k) * c)"
huffman@29981
   391
    unfolding dvd_def by (simp add: mult_ac)
huffman@29981
   392
  also have "(\<exists>k. b * c = (a * k) * c) \<longleftrightarrow> c = 0 \<or> a dvd b"
huffman@29981
   393
    unfolding dvd_def by simp
huffman@29981
   394
  finally show ?thesis .
huffman@29981
   395
qed
huffman@29981
   396
huffman@29981
   397
lemma dvd_mult_cancel_left [simp]:
huffman@29981
   398
  "c * a dvd c * b \<longleftrightarrow> c = 0 \<or> a dvd b"
huffman@29981
   399
proof -
huffman@29981
   400
  have "c * a dvd c * b \<longleftrightarrow> (\<exists>k. b * c = (a * k) * c)"
huffman@29981
   401
    unfolding dvd_def by (simp add: mult_ac)
huffman@29981
   402
  also have "(\<exists>k. b * c = (a * k) * c) \<longleftrightarrow> c = 0 \<or> a dvd b"
huffman@29981
   403
    unfolding dvd_def by simp
huffman@29981
   404
  finally show ?thesis .
huffman@29981
   405
qed
huffman@29981
   406
haftmann@25186
   407
end
haftmann@25152
   408
haftmann@35083
   409
class inverse =
haftmann@35083
   410
  fixes inverse :: "'a \<Rightarrow> 'a"
haftmann@35083
   411
    and divide :: "'a \<Rightarrow> 'a \<Rightarrow> 'a"  (infixl "'/" 70)
haftmann@35083
   412
haftmann@22390
   413
class division_ring = ring_1 + inverse +
haftmann@25062
   414
  assumes left_inverse [simp]:  "a \<noteq> 0 \<Longrightarrow> inverse a * a = 1"
haftmann@25062
   415
  assumes right_inverse [simp]: "a \<noteq> 0 \<Longrightarrow> a * inverse a = 1"
haftmann@35083
   416
  assumes divide_inverse: "a / b = a * inverse b"
haftmann@25186
   417
begin
huffman@20496
   418
haftmann@25186
   419
subclass ring_1_no_zero_divisors
haftmann@28823
   420
proof
huffman@22987
   421
  fix a b :: 'a
huffman@22987
   422
  assume a: "a \<noteq> 0" and b: "b \<noteq> 0"
huffman@22987
   423
  show "a * b \<noteq> 0"
huffman@22987
   424
  proof
huffman@22987
   425
    assume ab: "a * b = 0"
nipkow@29667
   426
    hence "0 = inverse a * (a * b) * inverse b" by simp
huffman@22987
   427
    also have "\<dots> = (inverse a * a) * (b * inverse b)"
huffman@22987
   428
      by (simp only: mult_assoc)
nipkow@29667
   429
    also have "\<dots> = 1" using a b by simp
nipkow@29667
   430
    finally show False by simp
huffman@22987
   431
  qed
huffman@22987
   432
qed
huffman@20496
   433
haftmann@26274
   434
lemma nonzero_imp_inverse_nonzero:
haftmann@26274
   435
  "a \<noteq> 0 \<Longrightarrow> inverse a \<noteq> 0"
haftmann@26274
   436
proof
haftmann@26274
   437
  assume ianz: "inverse a = 0"
haftmann@26274
   438
  assume "a \<noteq> 0"
haftmann@26274
   439
  hence "1 = a * inverse a" by simp
haftmann@26274
   440
  also have "... = 0" by (simp add: ianz)
haftmann@26274
   441
  finally have "1 = 0" .
haftmann@26274
   442
  thus False by (simp add: eq_commute)
haftmann@26274
   443
qed
haftmann@26274
   444
haftmann@26274
   445
lemma inverse_zero_imp_zero:
haftmann@26274
   446
  "inverse a = 0 \<Longrightarrow> a = 0"
haftmann@26274
   447
apply (rule classical)
haftmann@26274
   448
apply (drule nonzero_imp_inverse_nonzero)
haftmann@26274
   449
apply auto
haftmann@26274
   450
done
haftmann@26274
   451
haftmann@26274
   452
lemma inverse_unique: 
haftmann@26274
   453
  assumes ab: "a * b = 1"
haftmann@26274
   454
  shows "inverse a = b"
haftmann@26274
   455
proof -
haftmann@26274
   456
  have "a \<noteq> 0" using ab by (cases "a = 0") simp_all
huffman@29406
   457
  moreover have "inverse a * (a * b) = inverse a" by (simp add: ab)
huffman@29406
   458
  ultimately show ?thesis by (simp add: mult_assoc [symmetric])
haftmann@26274
   459
qed
haftmann@26274
   460
huffman@29406
   461
lemma nonzero_inverse_minus_eq:
huffman@29406
   462
  "a \<noteq> 0 \<Longrightarrow> inverse (- a) = - inverse a"
nipkow@29667
   463
by (rule inverse_unique) simp
huffman@29406
   464
huffman@29406
   465
lemma nonzero_inverse_inverse_eq:
huffman@29406
   466
  "a \<noteq> 0 \<Longrightarrow> inverse (inverse a) = a"
nipkow@29667
   467
by (rule inverse_unique) simp
huffman@29406
   468
huffman@29406
   469
lemma nonzero_inverse_eq_imp_eq:
huffman@29406
   470
  assumes "inverse a = inverse b" and "a \<noteq> 0" and "b \<noteq> 0"
huffman@29406
   471
  shows "a = b"
huffman@29406
   472
proof -
huffman@29406
   473
  from `inverse a = inverse b`
nipkow@29667
   474
  have "inverse (inverse a) = inverse (inverse b)" by (rule arg_cong)
huffman@29406
   475
  with `a \<noteq> 0` and `b \<noteq> 0` show "a = b"
huffman@29406
   476
    by (simp add: nonzero_inverse_inverse_eq)
huffman@29406
   477
qed
huffman@29406
   478
huffman@29406
   479
lemma inverse_1 [simp]: "inverse 1 = 1"
nipkow@29667
   480
by (rule inverse_unique) simp
huffman@29406
   481
haftmann@26274
   482
lemma nonzero_inverse_mult_distrib: 
huffman@29406
   483
  assumes "a \<noteq> 0" and "b \<noteq> 0"
haftmann@26274
   484
  shows "inverse (a * b) = inverse b * inverse a"
haftmann@26274
   485
proof -
nipkow@29667
   486
  have "a * (b * inverse b) * inverse a = 1" using assms by simp
nipkow@29667
   487
  hence "a * b * (inverse b * inverse a) = 1" by (simp only: mult_assoc)
nipkow@29667
   488
  thus ?thesis by (rule inverse_unique)
haftmann@26274
   489
qed
haftmann@26274
   490
haftmann@26274
   491
lemma division_ring_inverse_add:
haftmann@26274
   492
  "a \<noteq> 0 \<Longrightarrow> b \<noteq> 0 \<Longrightarrow> inverse a + inverse b = inverse a * (a + b) * inverse b"
nipkow@29667
   493
by (simp add: algebra_simps)
haftmann@26274
   494
haftmann@26274
   495
lemma division_ring_inverse_diff:
haftmann@26274
   496
  "a \<noteq> 0 \<Longrightarrow> b \<noteq> 0 \<Longrightarrow> inverse a - inverse b = inverse a * (b - a) * inverse b"
nipkow@29667
   497
by (simp add: algebra_simps)
haftmann@26274
   498
haftmann@36301
   499
lemma right_inverse_eq: "b \<noteq> 0 \<Longrightarrow> a / b = 1 \<longleftrightarrow> a = b"
haftmann@36301
   500
proof
haftmann@36301
   501
  assume neq: "b \<noteq> 0"
haftmann@36301
   502
  {
haftmann@36301
   503
    hence "a = (a / b) * b" by (simp add: divide_inverse mult_assoc)
haftmann@36301
   504
    also assume "a / b = 1"
haftmann@36301
   505
    finally show "a = b" by simp
haftmann@36301
   506
  next
haftmann@36301
   507
    assume "a = b"
haftmann@36301
   508
    with neq show "a / b = 1" by (simp add: divide_inverse)
haftmann@36301
   509
  }
haftmann@36301
   510
qed
haftmann@36301
   511
haftmann@36301
   512
lemma nonzero_inverse_eq_divide: "a \<noteq> 0 \<Longrightarrow> inverse a = 1 / a"
haftmann@36301
   513
by (simp add: divide_inverse)
haftmann@36301
   514
haftmann@36301
   515
lemma divide_self [simp]: "a \<noteq> 0 \<Longrightarrow> a / a = 1"
haftmann@36301
   516
by (simp add: divide_inverse)
haftmann@36301
   517
haftmann@36301
   518
lemma divide_zero_left [simp]: "0 / a = 0"
haftmann@36301
   519
by (simp add: divide_inverse)
haftmann@36301
   520
haftmann@36301
   521
lemma inverse_eq_divide: "inverse a = 1 / a"
haftmann@36301
   522
by (simp add: divide_inverse)
haftmann@36301
   523
haftmann@36301
   524
lemma add_divide_distrib: "(a+b) / c = a/c + b/c"
haftmann@36301
   525
by (simp add: divide_inverse algebra_simps)
haftmann@36301
   526
haftmann@36301
   527
lemma divide_1 [simp]: "a / 1 = a"
haftmann@36301
   528
  by (simp add: divide_inverse)
haftmann@36301
   529
haftmann@36304
   530
lemma times_divide_eq_right [simp]: "a * (b / c) = (a * b) / c"
haftmann@36301
   531
  by (simp add: divide_inverse mult_assoc)
haftmann@36301
   532
haftmann@36301
   533
lemma minus_divide_left: "- (a / b) = (-a) / b"
haftmann@36301
   534
  by (simp add: divide_inverse)
haftmann@36301
   535
haftmann@36301
   536
lemma nonzero_minus_divide_right: "b \<noteq> 0 ==> - (a / b) = a / (- b)"
haftmann@36301
   537
  by (simp add: divide_inverse nonzero_inverse_minus_eq)
haftmann@36301
   538
haftmann@36301
   539
lemma nonzero_minus_divide_divide: "b \<noteq> 0 ==> (-a) / (-b) = a / b"
haftmann@36301
   540
  by (simp add: divide_inverse nonzero_inverse_minus_eq)
haftmann@36301
   541
haftmann@36301
   542
lemma divide_minus_left [simp, no_atp]: "(-a) / b = - (a / b)"
haftmann@36301
   543
  by (simp add: divide_inverse)
haftmann@36301
   544
haftmann@36301
   545
lemma diff_divide_distrib: "(a - b) / c = a / c - b / c"
haftmann@36301
   546
  by (simp add: diff_minus add_divide_distrib)
haftmann@36301
   547
haftmann@36348
   548
lemma nonzero_eq_divide_eq [field_simps]: "c \<noteq> 0 \<Longrightarrow> a = b / c \<longleftrightarrow> a * c = b"
haftmann@36301
   549
proof -
haftmann@36301
   550
  assume [simp]: "c \<noteq> 0"
haftmann@36301
   551
  have "a = b / c \<longleftrightarrow> a * c = (b / c) * c" by simp
haftmann@36301
   552
  also have "... \<longleftrightarrow> a * c = b" by (simp add: divide_inverse mult_assoc)
haftmann@36301
   553
  finally show ?thesis .
haftmann@36301
   554
qed
haftmann@36301
   555
haftmann@36348
   556
lemma nonzero_divide_eq_eq [field_simps]: "c \<noteq> 0 \<Longrightarrow> b / c = a \<longleftrightarrow> b = a * c"
haftmann@36301
   557
proof -
haftmann@36301
   558
  assume [simp]: "c \<noteq> 0"
haftmann@36301
   559
  have "b / c = a \<longleftrightarrow> (b / c) * c = a * c" by simp
haftmann@36301
   560
  also have "... \<longleftrightarrow> b = a * c" by (simp add: divide_inverse mult_assoc) 
haftmann@36301
   561
  finally show ?thesis .
haftmann@36301
   562
qed
haftmann@36301
   563
haftmann@36301
   564
lemma divide_eq_imp: "c \<noteq> 0 \<Longrightarrow> b = a * c \<Longrightarrow> b / c = a"
haftmann@36301
   565
  by (simp add: divide_inverse mult_assoc)
haftmann@36301
   566
haftmann@36301
   567
lemma eq_divide_imp: "c \<noteq> 0 \<Longrightarrow> a * c = b \<Longrightarrow> a = b / c"
haftmann@36301
   568
  by (drule sym) (simp add: divide_inverse mult_assoc)
haftmann@36301
   569
haftmann@36301
   570
end
haftmann@36301
   571
haftmann@36348
   572
class division_ring_inverse_zero = division_ring +
haftmann@36301
   573
  assumes inverse_zero [simp]: "inverse 0 = 0"
haftmann@36301
   574
begin
haftmann@36301
   575
haftmann@36301
   576
lemma divide_zero [simp]:
haftmann@36301
   577
  "a / 0 = 0"
haftmann@36301
   578
  by (simp add: divide_inverse)
haftmann@36301
   579
haftmann@36301
   580
lemma divide_self_if [simp]:
haftmann@36301
   581
  "a / a = (if a = 0 then 0 else 1)"
haftmann@36301
   582
  by simp
haftmann@36301
   583
haftmann@36301
   584
lemma inverse_nonzero_iff_nonzero [simp]:
haftmann@36301
   585
  "inverse a = 0 \<longleftrightarrow> a = 0"
haftmann@36301
   586
  by rule (fact inverse_zero_imp_zero, simp)
haftmann@36301
   587
haftmann@36301
   588
lemma inverse_minus_eq [simp]:
haftmann@36301
   589
  "inverse (- a) = - inverse a"
haftmann@36301
   590
proof cases
haftmann@36301
   591
  assume "a=0" thus ?thesis by simp
haftmann@36301
   592
next
haftmann@36301
   593
  assume "a\<noteq>0" 
haftmann@36301
   594
  thus ?thesis by (simp add: nonzero_inverse_minus_eq)
haftmann@36301
   595
qed
haftmann@36301
   596
haftmann@36301
   597
lemma inverse_eq_imp_eq:
haftmann@36301
   598
  "inverse a = inverse b \<Longrightarrow> a = b"
haftmann@36301
   599
apply (cases "a=0 | b=0") 
haftmann@36301
   600
 apply (force dest!: inverse_zero_imp_zero
haftmann@36301
   601
              simp add: eq_commute [of "0::'a"])
haftmann@36301
   602
apply (force dest!: nonzero_inverse_eq_imp_eq) 
haftmann@36301
   603
done
haftmann@36301
   604
haftmann@36301
   605
lemma inverse_eq_iff_eq [simp]:
haftmann@36301
   606
  "inverse a = inverse b \<longleftrightarrow> a = b"
haftmann@36301
   607
  by (force dest!: inverse_eq_imp_eq)
haftmann@36301
   608
haftmann@36301
   609
lemma inverse_inverse_eq [simp]:
haftmann@36301
   610
  "inverse (inverse a) = a"
haftmann@36301
   611
proof cases
haftmann@36301
   612
  assume "a=0" thus ?thesis by simp
haftmann@36301
   613
next
haftmann@36301
   614
  assume "a\<noteq>0" 
haftmann@36301
   615
  thus ?thesis by (simp add: nonzero_inverse_inverse_eq)
haftmann@36301
   616
qed
haftmann@36301
   617
haftmann@25186
   618
end
haftmann@25152
   619
haftmann@22390
   620
class mult_mono = times + zero + ord +
haftmann@25062
   621
  assumes mult_left_mono: "a \<le> b \<Longrightarrow> 0 \<le> c \<Longrightarrow> c * a \<le> c * b"
haftmann@25062
   622
  assumes mult_right_mono: "a \<le> b \<Longrightarrow> 0 \<le> c \<Longrightarrow> a * c \<le> b * c"
paulson@14267
   623
haftmann@35302
   624
text {*
haftmann@35302
   625
  The theory of partially ordered rings is taken from the books:
haftmann@35302
   626
  \begin{itemize}
haftmann@35302
   627
  \item \emph{Lattice Theory} by Garret Birkhoff, American Mathematical Society 1979 
haftmann@35302
   628
  \item \emph{Partially Ordered Algebraic Systems}, Pergamon Press 1963
haftmann@35302
   629
  \end{itemize}
haftmann@35302
   630
  Most of the used notions can also be looked up in 
haftmann@35302
   631
  \begin{itemize}
haftmann@35302
   632
  \item \url{http://www.mathworld.com} by Eric Weisstein et. al.
haftmann@35302
   633
  \item \emph{Algebra I} by van der Waerden, Springer.
haftmann@35302
   634
  \end{itemize}
haftmann@35302
   635
*}
haftmann@35302
   636
haftmann@35028
   637
class ordered_semiring = mult_mono + semiring_0 + ordered_ab_semigroup_add 
haftmann@25230
   638
begin
haftmann@25230
   639
haftmann@25230
   640
lemma mult_mono:
haftmann@25230
   641
  "a \<le> b \<Longrightarrow> c \<le> d \<Longrightarrow> 0 \<le> b \<Longrightarrow> 0 \<le> c
haftmann@25230
   642
     \<Longrightarrow> a * c \<le> b * d"
haftmann@25230
   643
apply (erule mult_right_mono [THEN order_trans], assumption)
haftmann@25230
   644
apply (erule mult_left_mono, assumption)
haftmann@25230
   645
done
haftmann@25230
   646
haftmann@25230
   647
lemma mult_mono':
haftmann@25230
   648
  "a \<le> b \<Longrightarrow> c \<le> d \<Longrightarrow> 0 \<le> a \<Longrightarrow> 0 \<le> c
haftmann@25230
   649
     \<Longrightarrow> a * c \<le> b * d"
haftmann@25230
   650
apply (rule mult_mono)
haftmann@25230
   651
apply (fast intro: order_trans)+
haftmann@25230
   652
done
haftmann@25230
   653
haftmann@25230
   654
end
krauss@21199
   655
haftmann@35028
   656
class ordered_cancel_semiring = mult_mono + ordered_ab_semigroup_add
huffman@29904
   657
  + semiring + cancel_comm_monoid_add
haftmann@25267
   658
begin
paulson@14268
   659
huffman@27516
   660
subclass semiring_0_cancel ..
haftmann@35028
   661
subclass ordered_semiring ..
obua@23521
   662
haftmann@25230
   663
lemma mult_nonneg_nonneg: "0 \<le> a \<Longrightarrow> 0 \<le> b \<Longrightarrow> 0 \<le> a * b"
haftmann@36301
   664
using mult_left_mono [of 0 b a] by simp
haftmann@25230
   665
haftmann@25230
   666
lemma mult_nonneg_nonpos: "0 \<le> a \<Longrightarrow> b \<le> 0 \<Longrightarrow> a * b \<le> 0"
haftmann@36301
   667
using mult_left_mono [of b 0 a] by simp
huffman@30692
   668
huffman@30692
   669
lemma mult_nonpos_nonneg: "a \<le> 0 \<Longrightarrow> 0 \<le> b \<Longrightarrow> a * b \<le> 0"
haftmann@36301
   670
using mult_right_mono [of a 0 b] by simp
huffman@30692
   671
huffman@30692
   672
text {* Legacy - use @{text mult_nonpos_nonneg} *}
haftmann@25230
   673
lemma mult_nonneg_nonpos2: "0 \<le> a \<Longrightarrow> b \<le> 0 \<Longrightarrow> b * a \<le> 0" 
haftmann@36301
   674
by (drule mult_right_mono [of b 0], auto)
haftmann@25230
   675
haftmann@26234
   676
lemma split_mult_neg_le: "(0 \<le> a & b \<le> 0) | (a \<le> 0 & 0 \<le> b) \<Longrightarrow> a * b \<le> 0" 
nipkow@29667
   677
by (auto simp add: mult_nonneg_nonpos mult_nonneg_nonpos2)
haftmann@25230
   678
haftmann@25230
   679
end
haftmann@25230
   680
haftmann@35028
   681
class linordered_semiring = semiring + comm_monoid_add + linordered_cancel_ab_semigroup_add + mult_mono
haftmann@25267
   682
begin
haftmann@25230
   683
haftmann@35028
   684
subclass ordered_cancel_semiring ..
haftmann@35028
   685
haftmann@35028
   686
subclass ordered_comm_monoid_add ..
haftmann@25304
   687
haftmann@25230
   688
lemma mult_left_less_imp_less:
haftmann@25230
   689
  "c * a < c * b \<Longrightarrow> 0 \<le> c \<Longrightarrow> a < b"
nipkow@29667
   690
by (force simp add: mult_left_mono not_le [symmetric])
haftmann@25230
   691
 
haftmann@25230
   692
lemma mult_right_less_imp_less:
haftmann@25230
   693
  "a * c < b * c \<Longrightarrow> 0 \<le> c \<Longrightarrow> a < b"
nipkow@29667
   694
by (force simp add: mult_right_mono not_le [symmetric])
obua@23521
   695
haftmann@25186
   696
end
haftmann@25152
   697
haftmann@35043
   698
class linordered_semiring_1 = linordered_semiring + semiring_1
hoelzl@36622
   699
begin
hoelzl@36622
   700
hoelzl@36622
   701
lemma convex_bound_le:
hoelzl@36622
   702
  assumes "x \<le> a" "y \<le> a" "0 \<le> u" "0 \<le> v" "u + v = 1"
hoelzl@36622
   703
  shows "u * x + v * y \<le> a"
hoelzl@36622
   704
proof-
hoelzl@36622
   705
  from assms have "u * x + v * y \<le> u * a + v * a"
hoelzl@36622
   706
    by (simp add: add_mono mult_left_mono)
hoelzl@36622
   707
  thus ?thesis using assms unfolding left_distrib[symmetric] by simp
hoelzl@36622
   708
qed
hoelzl@36622
   709
hoelzl@36622
   710
end
haftmann@35043
   711
haftmann@35043
   712
class linordered_semiring_strict = semiring + comm_monoid_add + linordered_cancel_ab_semigroup_add +
haftmann@25062
   713
  assumes mult_strict_left_mono: "a < b \<Longrightarrow> 0 < c \<Longrightarrow> c * a < c * b"
haftmann@25062
   714
  assumes mult_strict_right_mono: "a < b \<Longrightarrow> 0 < c \<Longrightarrow> a * c < b * c"
haftmann@25267
   715
begin
paulson@14341
   716
huffman@27516
   717
subclass semiring_0_cancel ..
obua@14940
   718
haftmann@35028
   719
subclass linordered_semiring
haftmann@28823
   720
proof
huffman@23550
   721
  fix a b c :: 'a
huffman@23550
   722
  assume A: "a \<le> b" "0 \<le> c"
huffman@23550
   723
  from A show "c * a \<le> c * b"
haftmann@25186
   724
    unfolding le_less
haftmann@25186
   725
    using mult_strict_left_mono by (cases "c = 0") auto
huffman@23550
   726
  from A show "a * c \<le> b * c"
haftmann@25152
   727
    unfolding le_less
haftmann@25186
   728
    using mult_strict_right_mono by (cases "c = 0") auto
haftmann@25152
   729
qed
haftmann@25152
   730
haftmann@25230
   731
lemma mult_left_le_imp_le:
haftmann@25230
   732
  "c * a \<le> c * b \<Longrightarrow> 0 < c \<Longrightarrow> a \<le> b"
nipkow@29667
   733
by (force simp add: mult_strict_left_mono _not_less [symmetric])
haftmann@25230
   734
 
haftmann@25230
   735
lemma mult_right_le_imp_le:
haftmann@25230
   736
  "a * c \<le> b * c \<Longrightarrow> 0 < c \<Longrightarrow> a \<le> b"
nipkow@29667
   737
by (force simp add: mult_strict_right_mono not_less [symmetric])
haftmann@25230
   738
huffman@30692
   739
lemma mult_pos_pos: "0 < a \<Longrightarrow> 0 < b \<Longrightarrow> 0 < a * b"
haftmann@36301
   740
using mult_strict_left_mono [of 0 b a] by simp
huffman@30692
   741
huffman@30692
   742
lemma mult_pos_neg: "0 < a \<Longrightarrow> b < 0 \<Longrightarrow> a * b < 0"
haftmann@36301
   743
using mult_strict_left_mono [of b 0 a] by simp
huffman@30692
   744
huffman@30692
   745
lemma mult_neg_pos: "a < 0 \<Longrightarrow> 0 < b \<Longrightarrow> a * b < 0"
haftmann@36301
   746
using mult_strict_right_mono [of a 0 b] by simp
huffman@30692
   747
huffman@30692
   748
text {* Legacy - use @{text mult_neg_pos} *}
huffman@30692
   749
lemma mult_pos_neg2: "0 < a \<Longrightarrow> b < 0 \<Longrightarrow> b * a < 0" 
haftmann@36301
   750
by (drule mult_strict_right_mono [of b 0], auto)
haftmann@25230
   751
haftmann@25230
   752
lemma zero_less_mult_pos:
haftmann@25230
   753
  "0 < a * b \<Longrightarrow> 0 < a \<Longrightarrow> 0 < b"
huffman@30692
   754
apply (cases "b\<le>0")
haftmann@25230
   755
 apply (auto simp add: le_less not_less)
huffman@30692
   756
apply (drule_tac mult_pos_neg [of a b])
haftmann@25230
   757
 apply (auto dest: less_not_sym)
haftmann@25230
   758
done
haftmann@25230
   759
haftmann@25230
   760
lemma zero_less_mult_pos2:
haftmann@25230
   761
  "0 < b * a \<Longrightarrow> 0 < a \<Longrightarrow> 0 < b"
huffman@30692
   762
apply (cases "b\<le>0")
haftmann@25230
   763
 apply (auto simp add: le_less not_less)
huffman@30692
   764
apply (drule_tac mult_pos_neg2 [of a b])
haftmann@25230
   765
 apply (auto dest: less_not_sym)
haftmann@25230
   766
done
haftmann@25230
   767
haftmann@26193
   768
text{*Strict monotonicity in both arguments*}
haftmann@26193
   769
lemma mult_strict_mono:
haftmann@26193
   770
  assumes "a < b" and "c < d" and "0 < b" and "0 \<le> c"
haftmann@26193
   771
  shows "a * c < b * d"
haftmann@26193
   772
  using assms apply (cases "c=0")
huffman@30692
   773
  apply (simp add: mult_pos_pos)
haftmann@26193
   774
  apply (erule mult_strict_right_mono [THEN less_trans])
huffman@30692
   775
  apply (force simp add: le_less)
haftmann@26193
   776
  apply (erule mult_strict_left_mono, assumption)
haftmann@26193
   777
  done
haftmann@26193
   778
haftmann@26193
   779
text{*This weaker variant has more natural premises*}
haftmann@26193
   780
lemma mult_strict_mono':
haftmann@26193
   781
  assumes "a < b" and "c < d" and "0 \<le> a" and "0 \<le> c"
haftmann@26193
   782
  shows "a * c < b * d"
nipkow@29667
   783
by (rule mult_strict_mono) (insert assms, auto)
haftmann@26193
   784
haftmann@26193
   785
lemma mult_less_le_imp_less:
haftmann@26193
   786
  assumes "a < b" and "c \<le> d" and "0 \<le> a" and "0 < c"
haftmann@26193
   787
  shows "a * c < b * d"
haftmann@26193
   788
  using assms apply (subgoal_tac "a * c < b * c")
haftmann@26193
   789
  apply (erule less_le_trans)
haftmann@26193
   790
  apply (erule mult_left_mono)
haftmann@26193
   791
  apply simp
haftmann@26193
   792
  apply (erule mult_strict_right_mono)
haftmann@26193
   793
  apply assumption
haftmann@26193
   794
  done
haftmann@26193
   795
haftmann@26193
   796
lemma mult_le_less_imp_less:
haftmann@26193
   797
  assumes "a \<le> b" and "c < d" and "0 < a" and "0 \<le> c"
haftmann@26193
   798
  shows "a * c < b * d"
haftmann@26193
   799
  using assms apply (subgoal_tac "a * c \<le> b * c")
haftmann@26193
   800
  apply (erule le_less_trans)
haftmann@26193
   801
  apply (erule mult_strict_left_mono)
haftmann@26193
   802
  apply simp
haftmann@26193
   803
  apply (erule mult_right_mono)
haftmann@26193
   804
  apply simp
haftmann@26193
   805
  done
haftmann@26193
   806
haftmann@26193
   807
lemma mult_less_imp_less_left:
haftmann@26193
   808
  assumes less: "c * a < c * b" and nonneg: "0 \<le> c"
haftmann@26193
   809
  shows "a < b"
haftmann@26193
   810
proof (rule ccontr)
haftmann@26193
   811
  assume "\<not>  a < b"
haftmann@26193
   812
  hence "b \<le> a" by (simp add: linorder_not_less)
haftmann@26193
   813
  hence "c * b \<le> c * a" using nonneg by (rule mult_left_mono)
nipkow@29667
   814
  with this and less show False by (simp add: not_less [symmetric])
haftmann@26193
   815
qed
haftmann@26193
   816
haftmann@26193
   817
lemma mult_less_imp_less_right:
haftmann@26193
   818
  assumes less: "a * c < b * c" and nonneg: "0 \<le> c"
haftmann@26193
   819
  shows "a < b"
haftmann@26193
   820
proof (rule ccontr)
haftmann@26193
   821
  assume "\<not> a < b"
haftmann@26193
   822
  hence "b \<le> a" by (simp add: linorder_not_less)
haftmann@26193
   823
  hence "b * c \<le> a * c" using nonneg by (rule mult_right_mono)
nipkow@29667
   824
  with this and less show False by (simp add: not_less [symmetric])
haftmann@26193
   825
qed  
haftmann@26193
   826
haftmann@25230
   827
end
haftmann@25230
   828
haftmann@35097
   829
class linordered_semiring_1_strict = linordered_semiring_strict + semiring_1
hoelzl@36622
   830
begin
hoelzl@36622
   831
hoelzl@36622
   832
subclass linordered_semiring_1 ..
hoelzl@36622
   833
hoelzl@36622
   834
lemma convex_bound_lt:
hoelzl@36622
   835
  assumes "x < a" "y < a" "0 \<le> u" "0 \<le> v" "u + v = 1"
hoelzl@36622
   836
  shows "u * x + v * y < a"
hoelzl@36622
   837
proof -
hoelzl@36622
   838
  from assms have "u * x + v * y < u * a + v * a"
hoelzl@36622
   839
    by (cases "u = 0")
hoelzl@36622
   840
       (auto intro!: add_less_le_mono mult_strict_left_mono mult_left_mono)
hoelzl@36622
   841
  thus ?thesis using assms unfolding left_distrib[symmetric] by simp
hoelzl@36622
   842
qed
hoelzl@36622
   843
hoelzl@36622
   844
end
haftmann@33319
   845
haftmann@22390
   846
class mult_mono1 = times + zero + ord +
haftmann@25230
   847
  assumes mult_mono1: "a \<le> b \<Longrightarrow> 0 \<le> c \<Longrightarrow> c * a \<le> c * b"
paulson@14270
   848
haftmann@35028
   849
class ordered_comm_semiring = comm_semiring_0
haftmann@35028
   850
  + ordered_ab_semigroup_add + mult_mono1
haftmann@25186
   851
begin
haftmann@25152
   852
haftmann@35028
   853
subclass ordered_semiring
haftmann@28823
   854
proof
krauss@21199
   855
  fix a b c :: 'a
huffman@23550
   856
  assume "a \<le> b" "0 \<le> c"
haftmann@25230
   857
  thus "c * a \<le> c * b" by (rule mult_mono1)
huffman@23550
   858
  thus "a * c \<le> b * c" by (simp only: mult_commute)
krauss@21199
   859
qed
paulson@14265
   860
haftmann@25267
   861
end
haftmann@25267
   862
haftmann@35028
   863
class ordered_cancel_comm_semiring = comm_semiring_0_cancel
haftmann@35028
   864
  + ordered_ab_semigroup_add + mult_mono1
haftmann@25267
   865
begin
paulson@14265
   866
haftmann@35028
   867
subclass ordered_comm_semiring ..
haftmann@35028
   868
subclass ordered_cancel_semiring ..
haftmann@25267
   869
haftmann@25267
   870
end
haftmann@25267
   871
haftmann@35028
   872
class linordered_comm_semiring_strict = comm_semiring_0 + linordered_cancel_ab_semigroup_add +
haftmann@26193
   873
  assumes mult_strict_left_mono_comm: "a < b \<Longrightarrow> 0 < c \<Longrightarrow> c * a < c * b"
haftmann@25267
   874
begin
haftmann@25267
   875
haftmann@35043
   876
subclass linordered_semiring_strict
haftmann@28823
   877
proof
huffman@23550
   878
  fix a b c :: 'a
huffman@23550
   879
  assume "a < b" "0 < c"
haftmann@26193
   880
  thus "c * a < c * b" by (rule mult_strict_left_mono_comm)
huffman@23550
   881
  thus "a * c < b * c" by (simp only: mult_commute)
huffman@23550
   882
qed
paulson@14272
   883
haftmann@35028
   884
subclass ordered_cancel_comm_semiring
haftmann@28823
   885
proof
huffman@23550
   886
  fix a b c :: 'a
huffman@23550
   887
  assume "a \<le> b" "0 \<le> c"
huffman@23550
   888
  thus "c * a \<le> c * b"
haftmann@25186
   889
    unfolding le_less
haftmann@26193
   890
    using mult_strict_left_mono by (cases "c = 0") auto
huffman@23550
   891
qed
paulson@14272
   892
haftmann@25267
   893
end
haftmann@25230
   894
haftmann@35028
   895
class ordered_ring = ring + ordered_cancel_semiring 
haftmann@25267
   896
begin
haftmann@25230
   897
haftmann@35028
   898
subclass ordered_ab_group_add ..
paulson@14270
   899
haftmann@25230
   900
lemma less_add_iff1:
haftmann@25230
   901
  "a * e + c < b * e + d \<longleftrightarrow> (a - b) * e + c < d"
nipkow@29667
   902
by (simp add: algebra_simps)
haftmann@25230
   903
haftmann@25230
   904
lemma less_add_iff2:
haftmann@25230
   905
  "a * e + c < b * e + d \<longleftrightarrow> c < (b - a) * e + d"
nipkow@29667
   906
by (simp add: algebra_simps)
haftmann@25230
   907
haftmann@25230
   908
lemma le_add_iff1:
haftmann@25230
   909
  "a * e + c \<le> b * e + d \<longleftrightarrow> (a - b) * e + c \<le> d"
nipkow@29667
   910
by (simp add: algebra_simps)
haftmann@25230
   911
haftmann@25230
   912
lemma le_add_iff2:
haftmann@25230
   913
  "a * e + c \<le> b * e + d \<longleftrightarrow> c \<le> (b - a) * e + d"
nipkow@29667
   914
by (simp add: algebra_simps)
haftmann@25230
   915
haftmann@25230
   916
lemma mult_left_mono_neg:
haftmann@25230
   917
  "b \<le> a \<Longrightarrow> c \<le> 0 \<Longrightarrow> c * a \<le> c * b"
haftmann@36301
   918
  apply (drule mult_left_mono [of _ _ "- c"])
huffman@35216
   919
  apply simp_all
haftmann@25230
   920
  done
haftmann@25230
   921
haftmann@25230
   922
lemma mult_right_mono_neg:
haftmann@25230
   923
  "b \<le> a \<Longrightarrow> c \<le> 0 \<Longrightarrow> a * c \<le> b * c"
haftmann@36301
   924
  apply (drule mult_right_mono [of _ _ "- c"])
huffman@35216
   925
  apply simp_all
haftmann@25230
   926
  done
haftmann@25230
   927
huffman@30692
   928
lemma mult_nonpos_nonpos: "a \<le> 0 \<Longrightarrow> b \<le> 0 \<Longrightarrow> 0 \<le> a * b"
haftmann@36301
   929
using mult_right_mono_neg [of a 0 b] by simp
haftmann@25230
   930
haftmann@25230
   931
lemma split_mult_pos_le:
haftmann@25230
   932
  "(0 \<le> a \<and> 0 \<le> b) \<or> (a \<le> 0 \<and> b \<le> 0) \<Longrightarrow> 0 \<le> a * b"
nipkow@29667
   933
by (auto simp add: mult_nonneg_nonneg mult_nonpos_nonpos)
haftmann@25186
   934
haftmann@25186
   935
end
paulson@14270
   936
haftmann@35028
   937
class linordered_ring = ring + linordered_semiring + linordered_ab_group_add + abs_if
haftmann@25304
   938
begin
haftmann@25304
   939
haftmann@35028
   940
subclass ordered_ring ..
haftmann@35028
   941
haftmann@35028
   942
subclass ordered_ab_group_add_abs
haftmann@28823
   943
proof
haftmann@25304
   944
  fix a b
haftmann@25304
   945
  show "\<bar>a + b\<bar> \<le> \<bar>a\<bar> + \<bar>b\<bar>"
huffman@35216
   946
    by (auto simp add: abs_if not_less)
huffman@35216
   947
    (auto simp del: minus_add_distrib simp add: minus_add_distrib [symmetric],
huffman@35216
   948
     auto intro: add_nonneg_nonneg, auto intro!: less_imp_le add_neg_neg)
huffman@35216
   949
qed (auto simp add: abs_if)
haftmann@25304
   950
huffman@35631
   951
lemma zero_le_square [simp]: "0 \<le> a * a"
huffman@35631
   952
  using linear [of 0 a]
huffman@35631
   953
  by (auto simp add: mult_nonneg_nonneg mult_nonpos_nonpos)
huffman@35631
   954
huffman@35631
   955
lemma not_square_less_zero [simp]: "\<not> (a * a < 0)"
huffman@35631
   956
  by (simp add: not_less)
huffman@35631
   957
haftmann@25304
   958
end
obua@23521
   959
haftmann@35028
   960
(* The "strict" suffix can be seen as describing the combination of linordered_ring and no_zero_divisors.
haftmann@35043
   961
   Basically, linordered_ring + no_zero_divisors = linordered_ring_strict.
haftmann@25230
   962
 *)
haftmann@35043
   963
class linordered_ring_strict = ring + linordered_semiring_strict
haftmann@25304
   964
  + ordered_ab_group_add + abs_if
haftmann@25230
   965
begin
paulson@14348
   966
haftmann@35028
   967
subclass linordered_ring ..
haftmann@25304
   968
huffman@30692
   969
lemma mult_strict_left_mono_neg: "b < a \<Longrightarrow> c < 0 \<Longrightarrow> c * a < c * b"
huffman@30692
   970
using mult_strict_left_mono [of b a "- c"] by simp
huffman@30692
   971
huffman@30692
   972
lemma mult_strict_right_mono_neg: "b < a \<Longrightarrow> c < 0 \<Longrightarrow> a * c < b * c"
huffman@30692
   973
using mult_strict_right_mono [of b a "- c"] by simp
huffman@30692
   974
huffman@30692
   975
lemma mult_neg_neg: "a < 0 \<Longrightarrow> b < 0 \<Longrightarrow> 0 < a * b"
haftmann@36301
   976
using mult_strict_right_mono_neg [of a 0 b] by simp
obua@14738
   977
haftmann@25917
   978
subclass ring_no_zero_divisors
haftmann@28823
   979
proof
haftmann@25917
   980
  fix a b
haftmann@25917
   981
  assume "a \<noteq> 0" then have A: "a < 0 \<or> 0 < a" by (simp add: neq_iff)
haftmann@25917
   982
  assume "b \<noteq> 0" then have B: "b < 0 \<or> 0 < b" by (simp add: neq_iff)
haftmann@25917
   983
  have "a * b < 0 \<or> 0 < a * b"
haftmann@25917
   984
  proof (cases "a < 0")
haftmann@25917
   985
    case True note A' = this
haftmann@25917
   986
    show ?thesis proof (cases "b < 0")
haftmann@25917
   987
      case True with A'
haftmann@25917
   988
      show ?thesis by (auto dest: mult_neg_neg)
haftmann@25917
   989
    next
haftmann@25917
   990
      case False with B have "0 < b" by auto
haftmann@25917
   991
      with A' show ?thesis by (auto dest: mult_strict_right_mono)
haftmann@25917
   992
    qed
haftmann@25917
   993
  next
haftmann@25917
   994
    case False with A have A': "0 < a" by auto
haftmann@25917
   995
    show ?thesis proof (cases "b < 0")
haftmann@25917
   996
      case True with A'
haftmann@25917
   997
      show ?thesis by (auto dest: mult_strict_right_mono_neg)
haftmann@25917
   998
    next
haftmann@25917
   999
      case False with B have "0 < b" by auto
haftmann@25917
  1000
      with A' show ?thesis by (auto dest: mult_pos_pos)
haftmann@25917
  1001
    qed
haftmann@25917
  1002
  qed
haftmann@25917
  1003
  then show "a * b \<noteq> 0" by (simp add: neq_iff)
haftmann@25917
  1004
qed
haftmann@25304
  1005
paulson@14265
  1006
lemma zero_less_mult_iff:
haftmann@25917
  1007
  "0 < a * b \<longleftrightarrow> 0 < a \<and> 0 < b \<or> a < 0 \<and> b < 0"
haftmann@25917
  1008
  apply (auto simp add: mult_pos_pos mult_neg_neg)
haftmann@25917
  1009
  apply (simp_all add: not_less le_less)
haftmann@25917
  1010
  apply (erule disjE) apply assumption defer
haftmann@25917
  1011
  apply (erule disjE) defer apply (drule sym) apply simp
haftmann@25917
  1012
  apply (erule disjE) defer apply (drule sym) apply simp
haftmann@25917
  1013
  apply (erule disjE) apply assumption apply (drule sym) apply simp
haftmann@25917
  1014
  apply (drule sym) apply simp
haftmann@25917
  1015
  apply (blast dest: zero_less_mult_pos)
haftmann@25230
  1016
  apply (blast dest: zero_less_mult_pos2)
haftmann@25230
  1017
  done
huffman@22990
  1018
paulson@14265
  1019
lemma zero_le_mult_iff:
haftmann@25917
  1020
  "0 \<le> a * b \<longleftrightarrow> 0 \<le> a \<and> 0 \<le> b \<or> a \<le> 0 \<and> b \<le> 0"
nipkow@29667
  1021
by (auto simp add: eq_commute [of 0] le_less not_less zero_less_mult_iff)
paulson@14265
  1022
paulson@14265
  1023
lemma mult_less_0_iff:
haftmann@25917
  1024
  "a * b < 0 \<longleftrightarrow> 0 < a \<and> b < 0 \<or> a < 0 \<and> 0 < b"
huffman@35216
  1025
  apply (insert zero_less_mult_iff [of "-a" b])
huffman@35216
  1026
  apply force
haftmann@25917
  1027
  done
paulson@14265
  1028
paulson@14265
  1029
lemma mult_le_0_iff:
haftmann@25917
  1030
  "a * b \<le> 0 \<longleftrightarrow> 0 \<le> a \<and> b \<le> 0 \<or> a \<le> 0 \<and> 0 \<le> b"
haftmann@25917
  1031
  apply (insert zero_le_mult_iff [of "-a" b]) 
huffman@35216
  1032
  apply force
haftmann@25917
  1033
  done
haftmann@25917
  1034
haftmann@26193
  1035
text{*Cancellation laws for @{term "c*a < c*b"} and @{term "a*c < b*c"},
haftmann@26193
  1036
   also with the relations @{text "\<le>"} and equality.*}
haftmann@26193
  1037
haftmann@26193
  1038
text{*These ``disjunction'' versions produce two cases when the comparison is
haftmann@26193
  1039
 an assumption, but effectively four when the comparison is a goal.*}
haftmann@26193
  1040
haftmann@26193
  1041
lemma mult_less_cancel_right_disj:
haftmann@26193
  1042
  "a * c < b * c \<longleftrightarrow> 0 < c \<and> a < b \<or> c < 0 \<and>  b < a"
haftmann@26193
  1043
  apply (cases "c = 0")
haftmann@26193
  1044
  apply (auto simp add: neq_iff mult_strict_right_mono 
haftmann@26193
  1045
                      mult_strict_right_mono_neg)
haftmann@26193
  1046
  apply (auto simp add: not_less 
haftmann@26193
  1047
                      not_le [symmetric, of "a*c"]
haftmann@26193
  1048
                      not_le [symmetric, of a])
haftmann@26193
  1049
  apply (erule_tac [!] notE)
haftmann@26193
  1050
  apply (auto simp add: less_imp_le mult_right_mono 
haftmann@26193
  1051
                      mult_right_mono_neg)
haftmann@26193
  1052
  done
haftmann@26193
  1053
haftmann@26193
  1054
lemma mult_less_cancel_left_disj:
haftmann@26193
  1055
  "c * a < c * b \<longleftrightarrow> 0 < c \<and> a < b \<or> c < 0 \<and>  b < a"
haftmann@26193
  1056
  apply (cases "c = 0")
haftmann@26193
  1057
  apply (auto simp add: neq_iff mult_strict_left_mono 
haftmann@26193
  1058
                      mult_strict_left_mono_neg)
haftmann@26193
  1059
  apply (auto simp add: not_less 
haftmann@26193
  1060
                      not_le [symmetric, of "c*a"]
haftmann@26193
  1061
                      not_le [symmetric, of a])
haftmann@26193
  1062
  apply (erule_tac [!] notE)
haftmann@26193
  1063
  apply (auto simp add: less_imp_le mult_left_mono 
haftmann@26193
  1064
                      mult_left_mono_neg)
haftmann@26193
  1065
  done
haftmann@26193
  1066
haftmann@26193
  1067
text{*The ``conjunction of implication'' lemmas produce two cases when the
haftmann@26193
  1068
comparison is a goal, but give four when the comparison is an assumption.*}
haftmann@26193
  1069
haftmann@26193
  1070
lemma mult_less_cancel_right:
haftmann@26193
  1071
  "a * c < b * c \<longleftrightarrow> (0 \<le> c \<longrightarrow> a < b) \<and> (c \<le> 0 \<longrightarrow> b < a)"
haftmann@26193
  1072
  using mult_less_cancel_right_disj [of a c b] by auto
haftmann@26193
  1073
haftmann@26193
  1074
lemma mult_less_cancel_left:
haftmann@26193
  1075
  "c * a < c * b \<longleftrightarrow> (0 \<le> c \<longrightarrow> a < b) \<and> (c \<le> 0 \<longrightarrow> b < a)"
haftmann@26193
  1076
  using mult_less_cancel_left_disj [of c a b] by auto
haftmann@26193
  1077
haftmann@26193
  1078
lemma mult_le_cancel_right:
haftmann@26193
  1079
   "a * c \<le> b * c \<longleftrightarrow> (0 < c \<longrightarrow> a \<le> b) \<and> (c < 0 \<longrightarrow> b \<le> a)"
nipkow@29667
  1080
by (simp add: not_less [symmetric] mult_less_cancel_right_disj)
haftmann@26193
  1081
haftmann@26193
  1082
lemma mult_le_cancel_left:
haftmann@26193
  1083
  "c * a \<le> c * b \<longleftrightarrow> (0 < c \<longrightarrow> a \<le> b) \<and> (c < 0 \<longrightarrow> b \<le> a)"
nipkow@29667
  1084
by (simp add: not_less [symmetric] mult_less_cancel_left_disj)
haftmann@26193
  1085
nipkow@30649
  1086
lemma mult_le_cancel_left_pos:
nipkow@30649
  1087
  "0 < c \<Longrightarrow> c * a \<le> c * b \<longleftrightarrow> a \<le> b"
nipkow@30649
  1088
by (auto simp: mult_le_cancel_left)
nipkow@30649
  1089
nipkow@30649
  1090
lemma mult_le_cancel_left_neg:
nipkow@30649
  1091
  "c < 0 \<Longrightarrow> c * a \<le> c * b \<longleftrightarrow> b \<le> a"
nipkow@30649
  1092
by (auto simp: mult_le_cancel_left)
nipkow@30649
  1093
nipkow@30649
  1094
lemma mult_less_cancel_left_pos:
nipkow@30649
  1095
  "0 < c \<Longrightarrow> c * a < c * b \<longleftrightarrow> a < b"
nipkow@30649
  1096
by (auto simp: mult_less_cancel_left)
nipkow@30649
  1097
nipkow@30649
  1098
lemma mult_less_cancel_left_neg:
nipkow@30649
  1099
  "c < 0 \<Longrightarrow> c * a < c * b \<longleftrightarrow> b < a"
nipkow@30649
  1100
by (auto simp: mult_less_cancel_left)
nipkow@30649
  1101
haftmann@25917
  1102
end
paulson@14265
  1103
huffman@30692
  1104
lemmas mult_sign_intros =
huffman@30692
  1105
  mult_nonneg_nonneg mult_nonneg_nonpos
huffman@30692
  1106
  mult_nonpos_nonneg mult_nonpos_nonpos
huffman@30692
  1107
  mult_pos_pos mult_pos_neg
huffman@30692
  1108
  mult_neg_pos mult_neg_neg
haftmann@25230
  1109
haftmann@35028
  1110
class ordered_comm_ring = comm_ring + ordered_comm_semiring
haftmann@25267
  1111
begin
haftmann@25230
  1112
haftmann@35028
  1113
subclass ordered_ring ..
haftmann@35028
  1114
subclass ordered_cancel_comm_semiring ..
haftmann@25230
  1115
haftmann@25267
  1116
end
haftmann@25230
  1117
haftmann@35028
  1118
class linordered_semidom = comm_semiring_1_cancel + linordered_comm_semiring_strict +
haftmann@35028
  1119
  (*previously linordered_semiring*)
haftmann@25230
  1120
  assumes zero_less_one [simp]: "0 < 1"
haftmann@25230
  1121
begin
haftmann@25230
  1122
haftmann@25230
  1123
lemma pos_add_strict:
haftmann@25230
  1124
  shows "0 < a \<Longrightarrow> b < c \<Longrightarrow> b < a + c"
haftmann@36301
  1125
  using add_strict_mono [of 0 a b c] by simp
haftmann@25230
  1126
haftmann@26193
  1127
lemma zero_le_one [simp]: "0 \<le> 1"
nipkow@29667
  1128
by (rule zero_less_one [THEN less_imp_le]) 
haftmann@26193
  1129
haftmann@26193
  1130
lemma not_one_le_zero [simp]: "\<not> 1 \<le> 0"
nipkow@29667
  1131
by (simp add: not_le) 
haftmann@26193
  1132
haftmann@26193
  1133
lemma not_one_less_zero [simp]: "\<not> 1 < 0"
nipkow@29667
  1134
by (simp add: not_less) 
haftmann@26193
  1135
haftmann@26193
  1136
lemma less_1_mult:
haftmann@26193
  1137
  assumes "1 < m" and "1 < n"
haftmann@26193
  1138
  shows "1 < m * n"
haftmann@26193
  1139
  using assms mult_strict_mono [of 1 m 1 n]
haftmann@26193
  1140
    by (simp add:  less_trans [OF zero_less_one]) 
haftmann@26193
  1141
haftmann@25230
  1142
end
haftmann@25230
  1143
haftmann@35028
  1144
class linordered_idom = comm_ring_1 +
haftmann@35028
  1145
  linordered_comm_semiring_strict + ordered_ab_group_add +
haftmann@25230
  1146
  abs_if + sgn_if
haftmann@35028
  1147
  (*previously linordered_ring*)
haftmann@25917
  1148
begin
haftmann@25917
  1149
hoelzl@36622
  1150
subclass linordered_semiring_1_strict ..
haftmann@35043
  1151
subclass linordered_ring_strict ..
haftmann@35028
  1152
subclass ordered_comm_ring ..
huffman@27516
  1153
subclass idom ..
haftmann@25917
  1154
haftmann@35028
  1155
subclass linordered_semidom
haftmann@28823
  1156
proof
haftmann@26193
  1157
  have "0 \<le> 1 * 1" by (rule zero_le_square)
haftmann@26193
  1158
  thus "0 < 1" by (simp add: le_less)
haftmann@25917
  1159
qed 
haftmann@25917
  1160
haftmann@35028
  1161
lemma linorder_neqE_linordered_idom:
haftmann@26193
  1162
  assumes "x \<noteq> y" obtains "x < y" | "y < x"
haftmann@26193
  1163
  using assms by (rule neqE)
haftmann@26193
  1164
haftmann@26274
  1165
text {* These cancellation simprules also produce two cases when the comparison is a goal. *}
haftmann@26274
  1166
haftmann@26274
  1167
lemma mult_le_cancel_right1:
haftmann@26274
  1168
  "c \<le> b * c \<longleftrightarrow> (0 < c \<longrightarrow> 1 \<le> b) \<and> (c < 0 \<longrightarrow> b \<le> 1)"
nipkow@29667
  1169
by (insert mult_le_cancel_right [of 1 c b], simp)
haftmann@26274
  1170
haftmann@26274
  1171
lemma mult_le_cancel_right2:
haftmann@26274
  1172
  "a * c \<le> c \<longleftrightarrow> (0 < c \<longrightarrow> a \<le> 1) \<and> (c < 0 \<longrightarrow> 1 \<le> a)"
nipkow@29667
  1173
by (insert mult_le_cancel_right [of a c 1], simp)
haftmann@26274
  1174
haftmann@26274
  1175
lemma mult_le_cancel_left1:
haftmann@26274
  1176
  "c \<le> c * b \<longleftrightarrow> (0 < c \<longrightarrow> 1 \<le> b) \<and> (c < 0 \<longrightarrow> b \<le> 1)"
nipkow@29667
  1177
by (insert mult_le_cancel_left [of c 1 b], simp)
haftmann@26274
  1178
haftmann@26274
  1179
lemma mult_le_cancel_left2:
haftmann@26274
  1180
  "c * a \<le> c \<longleftrightarrow> (0 < c \<longrightarrow> a \<le> 1) \<and> (c < 0 \<longrightarrow> 1 \<le> a)"
nipkow@29667
  1181
by (insert mult_le_cancel_left [of c a 1], simp)
haftmann@26274
  1182
haftmann@26274
  1183
lemma mult_less_cancel_right1:
haftmann@26274
  1184
  "c < b * c \<longleftrightarrow> (0 \<le> c \<longrightarrow> 1 < b) \<and> (c \<le> 0 \<longrightarrow> b < 1)"
nipkow@29667
  1185
by (insert mult_less_cancel_right [of 1 c b], simp)
haftmann@26274
  1186
haftmann@26274
  1187
lemma mult_less_cancel_right2:
haftmann@26274
  1188
  "a * c < c \<longleftrightarrow> (0 \<le> c \<longrightarrow> a < 1) \<and> (c \<le> 0 \<longrightarrow> 1 < a)"
nipkow@29667
  1189
by (insert mult_less_cancel_right [of a c 1], simp)
haftmann@26274
  1190
haftmann@26274
  1191
lemma mult_less_cancel_left1:
haftmann@26274
  1192
  "c < c * b \<longleftrightarrow> (0 \<le> c \<longrightarrow> 1 < b) \<and> (c \<le> 0 \<longrightarrow> b < 1)"
nipkow@29667
  1193
by (insert mult_less_cancel_left [of c 1 b], simp)
haftmann@26274
  1194
haftmann@26274
  1195
lemma mult_less_cancel_left2:
haftmann@26274
  1196
  "c * a < c \<longleftrightarrow> (0 \<le> c \<longrightarrow> a < 1) \<and> (c \<le> 0 \<longrightarrow> 1 < a)"
nipkow@29667
  1197
by (insert mult_less_cancel_left [of c a 1], simp)
haftmann@26274
  1198
haftmann@27651
  1199
lemma sgn_sgn [simp]:
haftmann@27651
  1200
  "sgn (sgn a) = sgn a"
nipkow@29700
  1201
unfolding sgn_if by simp
haftmann@27651
  1202
haftmann@27651
  1203
lemma sgn_0_0:
haftmann@27651
  1204
  "sgn a = 0 \<longleftrightarrow> a = 0"
nipkow@29700
  1205
unfolding sgn_if by simp
haftmann@27651
  1206
haftmann@27651
  1207
lemma sgn_1_pos:
haftmann@27651
  1208
  "sgn a = 1 \<longleftrightarrow> a > 0"
huffman@35216
  1209
unfolding sgn_if by simp
haftmann@27651
  1210
haftmann@27651
  1211
lemma sgn_1_neg:
haftmann@27651
  1212
  "sgn a = - 1 \<longleftrightarrow> a < 0"
huffman@35216
  1213
unfolding sgn_if by auto
haftmann@27651
  1214
haftmann@29940
  1215
lemma sgn_pos [simp]:
haftmann@29940
  1216
  "0 < a \<Longrightarrow> sgn a = 1"
haftmann@29940
  1217
unfolding sgn_1_pos .
haftmann@29940
  1218
haftmann@29940
  1219
lemma sgn_neg [simp]:
haftmann@29940
  1220
  "a < 0 \<Longrightarrow> sgn a = - 1"
haftmann@29940
  1221
unfolding sgn_1_neg .
haftmann@29940
  1222
haftmann@27651
  1223
lemma sgn_times:
haftmann@27651
  1224
  "sgn (a * b) = sgn a * sgn b"
nipkow@29667
  1225
by (auto simp add: sgn_if zero_less_mult_iff)
haftmann@27651
  1226
haftmann@36301
  1227
lemma abs_sgn: "\<bar>k\<bar> = k * sgn k"
nipkow@29700
  1228
unfolding sgn_if abs_if by auto
nipkow@29700
  1229
haftmann@29940
  1230
lemma sgn_greater [simp]:
haftmann@29940
  1231
  "0 < sgn a \<longleftrightarrow> 0 < a"
haftmann@29940
  1232
  unfolding sgn_if by auto
haftmann@29940
  1233
haftmann@29940
  1234
lemma sgn_less [simp]:
haftmann@29940
  1235
  "sgn a < 0 \<longleftrightarrow> a < 0"
haftmann@29940
  1236
  unfolding sgn_if by auto
haftmann@29940
  1237
haftmann@36301
  1238
lemma abs_dvd_iff [simp]: "\<bar>m\<bar> dvd k \<longleftrightarrow> m dvd k"
huffman@29949
  1239
  by (simp add: abs_if)
huffman@29949
  1240
haftmann@36301
  1241
lemma dvd_abs_iff [simp]: "m dvd \<bar>k\<bar> \<longleftrightarrow> m dvd k"
huffman@29949
  1242
  by (simp add: abs_if)
haftmann@29653
  1243
nipkow@33676
  1244
lemma dvd_if_abs_eq:
haftmann@36301
  1245
  "\<bar>l\<bar> = \<bar>k\<bar> \<Longrightarrow> l dvd k"
nipkow@33676
  1246
by(subst abs_dvd_iff[symmetric]) simp
nipkow@33676
  1247
haftmann@25917
  1248
end
haftmann@25230
  1249
haftmann@26274
  1250
text {* Simprules for comparisons where common factors can be cancelled. *}
paulson@15234
  1251
blanchet@35828
  1252
lemmas mult_compare_simps[no_atp] =
paulson@15234
  1253
    mult_le_cancel_right mult_le_cancel_left
paulson@15234
  1254
    mult_le_cancel_right1 mult_le_cancel_right2
paulson@15234
  1255
    mult_le_cancel_left1 mult_le_cancel_left2
paulson@15234
  1256
    mult_less_cancel_right mult_less_cancel_left
paulson@15234
  1257
    mult_less_cancel_right1 mult_less_cancel_right2
paulson@15234
  1258
    mult_less_cancel_left1 mult_less_cancel_left2
paulson@15234
  1259
    mult_cancel_right mult_cancel_left
paulson@15234
  1260
    mult_cancel_right1 mult_cancel_right2
paulson@15234
  1261
    mult_cancel_left1 mult_cancel_left2
paulson@15234
  1262
haftmann@36301
  1263
text {* Reasoning about inequalities with division *}
avigad@16775
  1264
haftmann@35028
  1265
context linordered_semidom
haftmann@25193
  1266
begin
haftmann@25193
  1267
haftmann@25193
  1268
lemma less_add_one: "a < a + 1"
paulson@14293
  1269
proof -
haftmann@25193
  1270
  have "a + 0 < a + 1"
nipkow@23482
  1271
    by (blast intro: zero_less_one add_strict_left_mono)
paulson@14293
  1272
  thus ?thesis by simp
paulson@14293
  1273
qed
paulson@14293
  1274
haftmann@25193
  1275
lemma zero_less_two: "0 < 1 + 1"
nipkow@29667
  1276
by (blast intro: less_trans zero_less_one less_add_one)
haftmann@25193
  1277
haftmann@25193
  1278
end
paulson@14365
  1279
haftmann@36301
  1280
context linordered_idom
haftmann@36301
  1281
begin
paulson@15234
  1282
haftmann@36301
  1283
lemma mult_right_le_one_le:
haftmann@36301
  1284
  "0 \<le> x \<Longrightarrow> 0 \<le> y \<Longrightarrow> y \<le> 1 \<Longrightarrow> x * y \<le> x"
haftmann@36301
  1285
  by (auto simp add: mult_le_cancel_left2)
haftmann@36301
  1286
haftmann@36301
  1287
lemma mult_left_le_one_le:
haftmann@36301
  1288
  "0 \<le> x \<Longrightarrow> 0 \<le> y \<Longrightarrow> y \<le> 1 \<Longrightarrow> y * x \<le> x"
haftmann@36301
  1289
  by (auto simp add: mult_le_cancel_right2)
haftmann@36301
  1290
haftmann@36301
  1291
end
haftmann@36301
  1292
haftmann@36301
  1293
text {* Absolute Value *}
paulson@14293
  1294
haftmann@35028
  1295
context linordered_idom
haftmann@25304
  1296
begin
haftmann@25304
  1297
haftmann@36301
  1298
lemma mult_sgn_abs:
haftmann@36301
  1299
  "sgn x * \<bar>x\<bar> = x"
haftmann@25304
  1300
  unfolding abs_if sgn_if by auto
haftmann@25304
  1301
haftmann@36301
  1302
lemma abs_one [simp]:
haftmann@36301
  1303
  "\<bar>1\<bar> = 1"
haftmann@36301
  1304
  by (simp add: abs_if zero_less_one [THEN less_not_sym])
haftmann@36301
  1305
haftmann@25304
  1306
end
nipkow@24491
  1307
haftmann@35028
  1308
class ordered_ring_abs = ordered_ring + ordered_ab_group_add_abs +
haftmann@25304
  1309
  assumes abs_eq_mult:
haftmann@25304
  1310
    "(0 \<le> a \<or> a \<le> 0) \<and> (0 \<le> b \<or> b \<le> 0) \<Longrightarrow> \<bar>a * b\<bar> = \<bar>a\<bar> * \<bar>b\<bar>"
haftmann@25304
  1311
haftmann@35028
  1312
context linordered_idom
haftmann@30961
  1313
begin
haftmann@30961
  1314
haftmann@35028
  1315
subclass ordered_ring_abs proof
huffman@35216
  1316
qed (auto simp add: abs_if not_less mult_less_0_iff)
haftmann@30961
  1317
haftmann@30961
  1318
lemma abs_mult:
haftmann@36301
  1319
  "\<bar>a * b\<bar> = \<bar>a\<bar> * \<bar>b\<bar>" 
haftmann@30961
  1320
  by (rule abs_eq_mult) auto
haftmann@30961
  1321
haftmann@30961
  1322
lemma abs_mult_self:
haftmann@36301
  1323
  "\<bar>a\<bar> * \<bar>a\<bar> = a * a"
haftmann@30961
  1324
  by (simp add: abs_if) 
haftmann@30961
  1325
paulson@14294
  1326
lemma abs_mult_less:
haftmann@36301
  1327
  "\<bar>a\<bar> < c \<Longrightarrow> \<bar>b\<bar> < d \<Longrightarrow> \<bar>a\<bar> * \<bar>b\<bar> < c * d"
paulson@14294
  1328
proof -
haftmann@36301
  1329
  assume ac: "\<bar>a\<bar> < c"
haftmann@36301
  1330
  hence cpos: "0<c" by (blast intro: le_less_trans abs_ge_zero)
haftmann@36301
  1331
  assume "\<bar>b\<bar> < d"
paulson@14294
  1332
  thus ?thesis by (simp add: ac cpos mult_strict_mono) 
paulson@14294
  1333
qed
paulson@14293
  1334
haftmann@36301
  1335
lemma less_minus_self_iff:
haftmann@36301
  1336
  "a < - a \<longleftrightarrow> a < 0"
haftmann@36301
  1337
  by (simp only: less_le less_eq_neg_nonpos equal_neg_zero)
obua@14738
  1338
haftmann@36301
  1339
lemma abs_less_iff:
haftmann@36301
  1340
  "\<bar>a\<bar> < b \<longleftrightarrow> a < b \<and> - a < b" 
haftmann@36301
  1341
  by (simp add: less_le abs_le_iff) (auto simp add: abs_if)
obua@14738
  1342
haftmann@36301
  1343
lemma abs_mult_pos:
haftmann@36301
  1344
  "0 \<le> x \<Longrightarrow> \<bar>y\<bar> * x = \<bar>y * x\<bar>"
haftmann@36301
  1345
  by (simp add: abs_mult)
haftmann@36301
  1346
haftmann@36301
  1347
end
avigad@16775
  1348
haftmann@33364
  1349
code_modulename SML
haftmann@35050
  1350
  Rings Arith
haftmann@33364
  1351
haftmann@33364
  1352
code_modulename OCaml
haftmann@35050
  1353
  Rings Arith
haftmann@33364
  1354
haftmann@33364
  1355
code_modulename Haskell
haftmann@35050
  1356
  Rings Arith
haftmann@33364
  1357
paulson@14265
  1358
end