src/HOL/Ring_and_Field.thy
author huffman
Tue Feb 17 06:59:33 2009 -0800 (2009-02-17)
changeset 29949 20a506b8256d
parent 29940 83b373f61d41
child 29981 7d0ed261b712
child 30240 5b25fee0362c
permissions -rw-r--r--
lemmas abs_dvd_iff, dvd_abs_iff
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(*  Title:   HOL/Ring_and_Field.thy
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    Author:  Gertrud Bauer, Steven Obua, Tobias Nipkow, Lawrence C Paulson, and Markus Wenzel,
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             with contributions by Jeremy Avigad
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*)
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header {* (Ordered) Rings and Fields *}
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theory Ring_and_Field
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imports OrderedGroup
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begin
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text {*
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  The theory of partially ordered rings is taken from the books:
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  \begin{itemize}
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  \item \emph{Lattice Theory} by Garret Birkhoff, American Mathematical Society 1979 
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  \item \emph{Partially Ordered Algebraic Systems}, Pergamon Press 1963
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  \end{itemize}
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  Most of the used notions can also be looked up in 
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  \begin{itemize}
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  \item \url{http://www.mathworld.com} by Eric Weisstein et. al.
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  \item \emph{Algebra I} by van der Waerden, Springer.
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  \end{itemize}
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*}
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class semiring = ab_semigroup_add + semigroup_mult +
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  assumes left_distrib[algebra_simps]: "(a + b) * c = a * c + b * c"
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  assumes right_distrib[algebra_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 [noatp, 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: "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: "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 ab: "a dvd b"
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    and "cd": "c dvd d"
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  shows "a * c dvd b * d"
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proof -
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  from ab obtain b' where "b = a * b'" ..
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  moreover from "cd" 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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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 equals_zero_I) (simp add: left_distrib [symmetric]) 
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lemma minus_mult_right: "- (a * b) = a * - b"
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by (rule equals_zero_I) (simp add: right_distrib [symmetric]) 
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text{*Extract signs from products*}
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lemmas mult_minus_left [simp, noatp] = minus_mult_left [symmetric]
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lemmas mult_minus_right [simp,noatp] = 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]: "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]: "(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[noatp] =
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  right_distrib left_distrib left_diff_distrib right_diff_distrib
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text{*Legacy - use @{text algebra_simps} *}
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lemmas ring_simps[noatp] = algebra_simps
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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[noatp] =
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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: "x dvd y \<Longrightarrow> x dvd z \<Longrightarrow> x dvd (y - z)"
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by (simp add: 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, noatp]:
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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 right_minus_eq)
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  thus ?thesis by (simp add: disj_commute right_minus_eq)
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qed
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lemma mult_cancel_left [simp, noatp]:
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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 right_minus_eq)
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  thus ?thesis by (simp add: right_minus_eq)
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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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haftmann@26274
   356
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@29915
   381
    by (simp add: right_minus_eq 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
haftmann@25186
   387
end
haftmann@25152
   388
haftmann@22390
   389
class division_ring = ring_1 + inverse +
haftmann@25062
   390
  assumes left_inverse [simp]:  "a \<noteq> 0 \<Longrightarrow> inverse a * a = 1"
haftmann@25062
   391
  assumes right_inverse [simp]: "a \<noteq> 0 \<Longrightarrow> a * inverse a = 1"
haftmann@25186
   392
begin
huffman@20496
   393
haftmann@25186
   394
subclass ring_1_no_zero_divisors
haftmann@28823
   395
proof
huffman@22987
   396
  fix a b :: 'a
huffman@22987
   397
  assume a: "a \<noteq> 0" and b: "b \<noteq> 0"
huffman@22987
   398
  show "a * b \<noteq> 0"
huffman@22987
   399
  proof
huffman@22987
   400
    assume ab: "a * b = 0"
nipkow@29667
   401
    hence "0 = inverse a * (a * b) * inverse b" by simp
huffman@22987
   402
    also have "\<dots> = (inverse a * a) * (b * inverse b)"
huffman@22987
   403
      by (simp only: mult_assoc)
nipkow@29667
   404
    also have "\<dots> = 1" using a b by simp
nipkow@29667
   405
    finally show False by simp
huffman@22987
   406
  qed
huffman@22987
   407
qed
huffman@20496
   408
haftmann@26274
   409
lemma nonzero_imp_inverse_nonzero:
haftmann@26274
   410
  "a \<noteq> 0 \<Longrightarrow> inverse a \<noteq> 0"
haftmann@26274
   411
proof
haftmann@26274
   412
  assume ianz: "inverse a = 0"
haftmann@26274
   413
  assume "a \<noteq> 0"
haftmann@26274
   414
  hence "1 = a * inverse a" by simp
haftmann@26274
   415
  also have "... = 0" by (simp add: ianz)
haftmann@26274
   416
  finally have "1 = 0" .
haftmann@26274
   417
  thus False by (simp add: eq_commute)
haftmann@26274
   418
qed
haftmann@26274
   419
haftmann@26274
   420
lemma inverse_zero_imp_zero:
haftmann@26274
   421
  "inverse a = 0 \<Longrightarrow> a = 0"
haftmann@26274
   422
apply (rule classical)
haftmann@26274
   423
apply (drule nonzero_imp_inverse_nonzero)
haftmann@26274
   424
apply auto
haftmann@26274
   425
done
haftmann@26274
   426
haftmann@26274
   427
lemma inverse_unique: 
haftmann@26274
   428
  assumes ab: "a * b = 1"
haftmann@26274
   429
  shows "inverse a = b"
haftmann@26274
   430
proof -
haftmann@26274
   431
  have "a \<noteq> 0" using ab by (cases "a = 0") simp_all
huffman@29406
   432
  moreover have "inverse a * (a * b) = inverse a" by (simp add: ab)
huffman@29406
   433
  ultimately show ?thesis by (simp add: mult_assoc [symmetric])
haftmann@26274
   434
qed
haftmann@26274
   435
huffman@29406
   436
lemma nonzero_inverse_minus_eq:
huffman@29406
   437
  "a \<noteq> 0 \<Longrightarrow> inverse (- a) = - inverse a"
nipkow@29667
   438
by (rule inverse_unique) simp
huffman@29406
   439
huffman@29406
   440
lemma nonzero_inverse_inverse_eq:
huffman@29406
   441
  "a \<noteq> 0 \<Longrightarrow> inverse (inverse a) = a"
nipkow@29667
   442
by (rule inverse_unique) simp
huffman@29406
   443
huffman@29406
   444
lemma nonzero_inverse_eq_imp_eq:
huffman@29406
   445
  assumes "inverse a = inverse b" and "a \<noteq> 0" and "b \<noteq> 0"
huffman@29406
   446
  shows "a = b"
huffman@29406
   447
proof -
huffman@29406
   448
  from `inverse a = inverse b`
nipkow@29667
   449
  have "inverse (inverse a) = inverse (inverse b)" by (rule arg_cong)
huffman@29406
   450
  with `a \<noteq> 0` and `b \<noteq> 0` show "a = b"
huffman@29406
   451
    by (simp add: nonzero_inverse_inverse_eq)
huffman@29406
   452
qed
huffman@29406
   453
huffman@29406
   454
lemma inverse_1 [simp]: "inverse 1 = 1"
nipkow@29667
   455
by (rule inverse_unique) simp
huffman@29406
   456
haftmann@26274
   457
lemma nonzero_inverse_mult_distrib: 
huffman@29406
   458
  assumes "a \<noteq> 0" and "b \<noteq> 0"
haftmann@26274
   459
  shows "inverse (a * b) = inverse b * inverse a"
haftmann@26274
   460
proof -
nipkow@29667
   461
  have "a * (b * inverse b) * inverse a = 1" using assms by simp
nipkow@29667
   462
  hence "a * b * (inverse b * inverse a) = 1" by (simp only: mult_assoc)
nipkow@29667
   463
  thus ?thesis by (rule inverse_unique)
haftmann@26274
   464
qed
haftmann@26274
   465
haftmann@26274
   466
lemma division_ring_inverse_add:
haftmann@26274
   467
  "a \<noteq> 0 \<Longrightarrow> b \<noteq> 0 \<Longrightarrow> inverse a + inverse b = inverse a * (a + b) * inverse b"
nipkow@29667
   468
by (simp add: algebra_simps)
haftmann@26274
   469
haftmann@26274
   470
lemma division_ring_inverse_diff:
haftmann@26274
   471
  "a \<noteq> 0 \<Longrightarrow> b \<noteq> 0 \<Longrightarrow> inverse a - inverse b = inverse a * (b - a) * inverse b"
nipkow@29667
   472
by (simp add: algebra_simps)
haftmann@26274
   473
haftmann@25186
   474
end
haftmann@25152
   475
huffman@22987
   476
class field = comm_ring_1 + inverse +
haftmann@25062
   477
  assumes field_inverse:  "a \<noteq> 0 \<Longrightarrow> inverse a * a = 1"
haftmann@25062
   478
  assumes divide_inverse: "a / b = a * inverse b"
haftmann@25267
   479
begin
huffman@20496
   480
haftmann@25267
   481
subclass division_ring
haftmann@28823
   482
proof
huffman@22987
   483
  fix a :: 'a
huffman@22987
   484
  assume "a \<noteq> 0"
huffman@22987
   485
  thus "inverse a * a = 1" by (rule field_inverse)
huffman@22987
   486
  thus "a * inverse a = 1" by (simp only: mult_commute)
obua@14738
   487
qed
haftmann@25230
   488
huffman@27516
   489
subclass idom ..
haftmann@25230
   490
haftmann@25230
   491
lemma right_inverse_eq: "b \<noteq> 0 \<Longrightarrow> a / b = 1 \<longleftrightarrow> a = b"
haftmann@25230
   492
proof
haftmann@25230
   493
  assume neq: "b \<noteq> 0"
haftmann@25230
   494
  {
haftmann@25230
   495
    hence "a = (a / b) * b" by (simp add: divide_inverse mult_ac)
haftmann@25230
   496
    also assume "a / b = 1"
haftmann@25230
   497
    finally show "a = b" by simp
haftmann@25230
   498
  next
haftmann@25230
   499
    assume "a = b"
haftmann@25230
   500
    with neq show "a / b = 1" by (simp add: divide_inverse)
haftmann@25230
   501
  }
haftmann@25230
   502
qed
haftmann@25230
   503
haftmann@25230
   504
lemma nonzero_inverse_eq_divide: "a \<noteq> 0 \<Longrightarrow> inverse a = 1 / a"
nipkow@29667
   505
by (simp add: divide_inverse)
haftmann@25230
   506
haftmann@25230
   507
lemma divide_self [simp]: "a \<noteq> 0 \<Longrightarrow> a / a = 1"
nipkow@29667
   508
by (simp add: divide_inverse)
haftmann@25230
   509
haftmann@25230
   510
lemma divide_zero_left [simp]: "0 / a = 0"
nipkow@29667
   511
by (simp add: divide_inverse)
haftmann@25230
   512
haftmann@25230
   513
lemma inverse_eq_divide: "inverse a = 1 / a"
nipkow@29667
   514
by (simp add: divide_inverse)
haftmann@25230
   515
haftmann@25230
   516
lemma add_divide_distrib: "(a+b) / c = a/c + b/c"
nipkow@29667
   517
by (simp add: divide_inverse algebra_simps) 
haftmann@25230
   518
haftmann@25230
   519
end
haftmann@25230
   520
haftmann@22390
   521
class division_by_zero = zero + inverse +
haftmann@25062
   522
  assumes inverse_zero [simp]: "inverse 0 = 0"
paulson@14265
   523
haftmann@25230
   524
lemma divide_zero [simp]:
haftmann@25230
   525
  "a / 0 = (0::'a::{field,division_by_zero})"
nipkow@29667
   526
by (simp add: divide_inverse)
haftmann@25230
   527
haftmann@25230
   528
lemma divide_self_if [simp]:
haftmann@25230
   529
  "a / (a::'a::{field,division_by_zero}) = (if a=0 then 0 else 1)"
nipkow@29667
   530
by simp
haftmann@25230
   531
haftmann@22390
   532
class mult_mono = times + zero + ord +
haftmann@25062
   533
  assumes mult_left_mono: "a \<le> b \<Longrightarrow> 0 \<le> c \<Longrightarrow> c * a \<le> c * b"
haftmann@25062
   534
  assumes mult_right_mono: "a \<le> b \<Longrightarrow> 0 \<le> c \<Longrightarrow> a * c \<le> b * c"
paulson@14267
   535
haftmann@22390
   536
class pordered_semiring = mult_mono + semiring_0 + pordered_ab_semigroup_add 
haftmann@25230
   537
begin
haftmann@25230
   538
haftmann@25230
   539
lemma mult_mono:
haftmann@25230
   540
  "a \<le> b \<Longrightarrow> c \<le> d \<Longrightarrow> 0 \<le> b \<Longrightarrow> 0 \<le> c
haftmann@25230
   541
     \<Longrightarrow> a * c \<le> b * d"
haftmann@25230
   542
apply (erule mult_right_mono [THEN order_trans], assumption)
haftmann@25230
   543
apply (erule mult_left_mono, assumption)
haftmann@25230
   544
done
haftmann@25230
   545
haftmann@25230
   546
lemma mult_mono':
haftmann@25230
   547
  "a \<le> b \<Longrightarrow> c \<le> d \<Longrightarrow> 0 \<le> a \<Longrightarrow> 0 \<le> c
haftmann@25230
   548
     \<Longrightarrow> a * c \<le> b * d"
haftmann@25230
   549
apply (rule mult_mono)
haftmann@25230
   550
apply (fast intro: order_trans)+
haftmann@25230
   551
done
haftmann@25230
   552
haftmann@25230
   553
end
krauss@21199
   554
haftmann@22390
   555
class pordered_cancel_semiring = mult_mono + pordered_ab_semigroup_add
huffman@29904
   556
  + semiring + cancel_comm_monoid_add
haftmann@25267
   557
begin
paulson@14268
   558
huffman@27516
   559
subclass semiring_0_cancel ..
huffman@27516
   560
subclass pordered_semiring ..
obua@23521
   561
haftmann@25230
   562
lemma mult_nonneg_nonneg: "0 \<le> a \<Longrightarrow> 0 \<le> b \<Longrightarrow> 0 \<le> a * b"
nipkow@29667
   563
by (drule mult_left_mono [of zero b], auto)
haftmann@25230
   564
haftmann@25230
   565
lemma mult_nonneg_nonpos: "0 \<le> a \<Longrightarrow> b \<le> 0 \<Longrightarrow> a * b \<le> 0"
nipkow@29667
   566
by (drule mult_left_mono [of b zero], auto)
haftmann@25230
   567
haftmann@25230
   568
lemma mult_nonneg_nonpos2: "0 \<le> a \<Longrightarrow> b \<le> 0 \<Longrightarrow> b * a \<le> 0" 
nipkow@29667
   569
by (drule mult_right_mono [of b zero], auto)
haftmann@25230
   570
haftmann@26234
   571
lemma split_mult_neg_le: "(0 \<le> a & b \<le> 0) | (a \<le> 0 & 0 \<le> b) \<Longrightarrow> a * b \<le> 0" 
nipkow@29667
   572
by (auto simp add: mult_nonneg_nonpos mult_nonneg_nonpos2)
haftmann@25230
   573
haftmann@25230
   574
end
haftmann@25230
   575
haftmann@25230
   576
class ordered_semiring = semiring + comm_monoid_add + ordered_cancel_ab_semigroup_add + mult_mono
haftmann@25267
   577
begin
haftmann@25230
   578
huffman@27516
   579
subclass pordered_cancel_semiring ..
haftmann@25512
   580
huffman@27516
   581
subclass pordered_comm_monoid_add ..
haftmann@25304
   582
haftmann@25230
   583
lemma mult_left_less_imp_less:
haftmann@25230
   584
  "c * a < c * b \<Longrightarrow> 0 \<le> c \<Longrightarrow> a < b"
nipkow@29667
   585
by (force simp add: mult_left_mono not_le [symmetric])
haftmann@25230
   586
 
haftmann@25230
   587
lemma mult_right_less_imp_less:
haftmann@25230
   588
  "a * c < b * c \<Longrightarrow> 0 \<le> c \<Longrightarrow> a < b"
nipkow@29667
   589
by (force simp add: mult_right_mono not_le [symmetric])
obua@23521
   590
haftmann@25186
   591
end
haftmann@25152
   592
haftmann@22390
   593
class ordered_semiring_strict = semiring + comm_monoid_add + ordered_cancel_ab_semigroup_add +
haftmann@25062
   594
  assumes mult_strict_left_mono: "a < b \<Longrightarrow> 0 < c \<Longrightarrow> c * a < c * b"
haftmann@25062
   595
  assumes mult_strict_right_mono: "a < b \<Longrightarrow> 0 < c \<Longrightarrow> a * c < b * c"
haftmann@25267
   596
begin
paulson@14341
   597
huffman@27516
   598
subclass semiring_0_cancel ..
obua@14940
   599
haftmann@25267
   600
subclass ordered_semiring
haftmann@28823
   601
proof
huffman@23550
   602
  fix a b c :: 'a
huffman@23550
   603
  assume A: "a \<le> b" "0 \<le> c"
huffman@23550
   604
  from A show "c * a \<le> c * b"
haftmann@25186
   605
    unfolding le_less
haftmann@25186
   606
    using mult_strict_left_mono by (cases "c = 0") auto
huffman@23550
   607
  from A show "a * c \<le> b * c"
haftmann@25152
   608
    unfolding le_less
haftmann@25186
   609
    using mult_strict_right_mono by (cases "c = 0") auto
haftmann@25152
   610
qed
haftmann@25152
   611
haftmann@25230
   612
lemma mult_left_le_imp_le:
haftmann@25230
   613
  "c * a \<le> c * b \<Longrightarrow> 0 < c \<Longrightarrow> a \<le> b"
nipkow@29667
   614
by (force simp add: mult_strict_left_mono _not_less [symmetric])
haftmann@25230
   615
 
haftmann@25230
   616
lemma mult_right_le_imp_le:
haftmann@25230
   617
  "a * c \<le> b * c \<Longrightarrow> 0 < c \<Longrightarrow> a \<le> b"
nipkow@29667
   618
by (force simp add: mult_strict_right_mono not_less [symmetric])
haftmann@25230
   619
haftmann@25230
   620
lemma mult_pos_pos:
haftmann@25230
   621
  "0 < a \<Longrightarrow> 0 < b \<Longrightarrow> 0 < a * b"
nipkow@29667
   622
by (drule mult_strict_left_mono [of zero b], auto)
haftmann@25230
   623
haftmann@25230
   624
lemma mult_pos_neg:
haftmann@25230
   625
  "0 < a \<Longrightarrow> b < 0 \<Longrightarrow> a * b < 0"
nipkow@29667
   626
by (drule mult_strict_left_mono [of b zero], auto)
haftmann@25230
   627
haftmann@25230
   628
lemma mult_pos_neg2:
haftmann@25230
   629
  "0 < a \<Longrightarrow> b < 0 \<Longrightarrow> b * a < 0" 
nipkow@29667
   630
by (drule mult_strict_right_mono [of b zero], auto)
haftmann@25230
   631
haftmann@25230
   632
lemma zero_less_mult_pos:
haftmann@25230
   633
  "0 < a * b \<Longrightarrow> 0 < a \<Longrightarrow> 0 < b"
haftmann@25230
   634
apply (cases "b\<le>0") 
haftmann@25230
   635
 apply (auto simp add: le_less not_less)
haftmann@25230
   636
apply (drule_tac mult_pos_neg [of a b]) 
haftmann@25230
   637
 apply (auto dest: less_not_sym)
haftmann@25230
   638
done
haftmann@25230
   639
haftmann@25230
   640
lemma zero_less_mult_pos2:
haftmann@25230
   641
  "0 < b * a \<Longrightarrow> 0 < a \<Longrightarrow> 0 < b"
haftmann@25230
   642
apply (cases "b\<le>0") 
haftmann@25230
   643
 apply (auto simp add: le_less not_less)
haftmann@25230
   644
apply (drule_tac mult_pos_neg2 [of a b]) 
haftmann@25230
   645
 apply (auto dest: less_not_sym)
haftmann@25230
   646
done
haftmann@25230
   647
haftmann@26193
   648
text{*Strict monotonicity in both arguments*}
haftmann@26193
   649
lemma mult_strict_mono:
haftmann@26193
   650
  assumes "a < b" and "c < d" and "0 < b" and "0 \<le> c"
haftmann@26193
   651
  shows "a * c < b * d"
haftmann@26193
   652
  using assms apply (cases "c=0")
haftmann@26193
   653
  apply (simp add: mult_pos_pos) 
haftmann@26193
   654
  apply (erule mult_strict_right_mono [THEN less_trans])
haftmann@26193
   655
  apply (force simp add: le_less) 
haftmann@26193
   656
  apply (erule mult_strict_left_mono, assumption)
haftmann@26193
   657
  done
haftmann@26193
   658
haftmann@26193
   659
text{*This weaker variant has more natural premises*}
haftmann@26193
   660
lemma mult_strict_mono':
haftmann@26193
   661
  assumes "a < b" and "c < d" and "0 \<le> a" and "0 \<le> c"
haftmann@26193
   662
  shows "a * c < b * d"
nipkow@29667
   663
by (rule mult_strict_mono) (insert assms, auto)
haftmann@26193
   664
haftmann@26193
   665
lemma mult_less_le_imp_less:
haftmann@26193
   666
  assumes "a < b" and "c \<le> d" and "0 \<le> a" and "0 < c"
haftmann@26193
   667
  shows "a * c < b * d"
haftmann@26193
   668
  using assms apply (subgoal_tac "a * c < b * c")
haftmann@26193
   669
  apply (erule less_le_trans)
haftmann@26193
   670
  apply (erule mult_left_mono)
haftmann@26193
   671
  apply simp
haftmann@26193
   672
  apply (erule mult_strict_right_mono)
haftmann@26193
   673
  apply assumption
haftmann@26193
   674
  done
haftmann@26193
   675
haftmann@26193
   676
lemma mult_le_less_imp_less:
haftmann@26193
   677
  assumes "a \<le> b" and "c < d" and "0 < a" and "0 \<le> c"
haftmann@26193
   678
  shows "a * c < b * d"
haftmann@26193
   679
  using assms apply (subgoal_tac "a * c \<le> b * c")
haftmann@26193
   680
  apply (erule le_less_trans)
haftmann@26193
   681
  apply (erule mult_strict_left_mono)
haftmann@26193
   682
  apply simp
haftmann@26193
   683
  apply (erule mult_right_mono)
haftmann@26193
   684
  apply simp
haftmann@26193
   685
  done
haftmann@26193
   686
haftmann@26193
   687
lemma mult_less_imp_less_left:
haftmann@26193
   688
  assumes less: "c * a < c * b" and nonneg: "0 \<le> c"
haftmann@26193
   689
  shows "a < b"
haftmann@26193
   690
proof (rule ccontr)
haftmann@26193
   691
  assume "\<not>  a < b"
haftmann@26193
   692
  hence "b \<le> a" by (simp add: linorder_not_less)
haftmann@26193
   693
  hence "c * b \<le> c * a" using nonneg by (rule mult_left_mono)
nipkow@29667
   694
  with this and less show False by (simp add: not_less [symmetric])
haftmann@26193
   695
qed
haftmann@26193
   696
haftmann@26193
   697
lemma mult_less_imp_less_right:
haftmann@26193
   698
  assumes less: "a * c < b * c" and nonneg: "0 \<le> c"
haftmann@26193
   699
  shows "a < b"
haftmann@26193
   700
proof (rule ccontr)
haftmann@26193
   701
  assume "\<not> a < b"
haftmann@26193
   702
  hence "b \<le> a" by (simp add: linorder_not_less)
haftmann@26193
   703
  hence "b * c \<le> a * c" using nonneg by (rule mult_right_mono)
nipkow@29667
   704
  with this and less show False by (simp add: not_less [symmetric])
haftmann@26193
   705
qed  
haftmann@26193
   706
haftmann@25230
   707
end
haftmann@25230
   708
haftmann@22390
   709
class mult_mono1 = times + zero + ord +
haftmann@25230
   710
  assumes mult_mono1: "a \<le> b \<Longrightarrow> 0 \<le> c \<Longrightarrow> c * a \<le> c * b"
paulson@14270
   711
haftmann@22390
   712
class pordered_comm_semiring = comm_semiring_0
haftmann@22390
   713
  + pordered_ab_semigroup_add + mult_mono1
haftmann@25186
   714
begin
haftmann@25152
   715
haftmann@25267
   716
subclass pordered_semiring
haftmann@28823
   717
proof
krauss@21199
   718
  fix a b c :: 'a
huffman@23550
   719
  assume "a \<le> b" "0 \<le> c"
haftmann@25230
   720
  thus "c * a \<le> c * b" by (rule mult_mono1)
huffman@23550
   721
  thus "a * c \<le> b * c" by (simp only: mult_commute)
krauss@21199
   722
qed
paulson@14265
   723
haftmann@25267
   724
end
haftmann@25267
   725
haftmann@25267
   726
class pordered_cancel_comm_semiring = comm_semiring_0_cancel
haftmann@25267
   727
  + pordered_ab_semigroup_add + mult_mono1
haftmann@25267
   728
begin
paulson@14265
   729
huffman@27516
   730
subclass pordered_comm_semiring ..
huffman@27516
   731
subclass pordered_cancel_semiring ..
haftmann@25267
   732
haftmann@25267
   733
end
haftmann@25267
   734
haftmann@25267
   735
class ordered_comm_semiring_strict = comm_semiring_0 + ordered_cancel_ab_semigroup_add +
haftmann@26193
   736
  assumes mult_strict_left_mono_comm: "a < b \<Longrightarrow> 0 < c \<Longrightarrow> c * a < c * b"
haftmann@25267
   737
begin
haftmann@25267
   738
haftmann@25267
   739
subclass ordered_semiring_strict
haftmann@28823
   740
proof
huffman@23550
   741
  fix a b c :: 'a
huffman@23550
   742
  assume "a < b" "0 < c"
haftmann@26193
   743
  thus "c * a < c * b" by (rule mult_strict_left_mono_comm)
huffman@23550
   744
  thus "a * c < b * c" by (simp only: mult_commute)
huffman@23550
   745
qed
paulson@14272
   746
haftmann@25267
   747
subclass pordered_cancel_comm_semiring
haftmann@28823
   748
proof
huffman@23550
   749
  fix a b c :: 'a
huffman@23550
   750
  assume "a \<le> b" "0 \<le> c"
huffman@23550
   751
  thus "c * a \<le> c * b"
haftmann@25186
   752
    unfolding le_less
haftmann@26193
   753
    using mult_strict_left_mono by (cases "c = 0") auto
huffman@23550
   754
qed
paulson@14272
   755
haftmann@25267
   756
end
haftmann@25230
   757
haftmann@25267
   758
class pordered_ring = ring + pordered_cancel_semiring 
haftmann@25267
   759
begin
haftmann@25230
   760
huffman@27516
   761
subclass pordered_ab_group_add ..
paulson@14270
   762
nipkow@29667
   763
text{*Legacy - use @{text algebra_simps} *}
nipkow@29833
   764
lemmas ring_simps[noatp] = algebra_simps
haftmann@25230
   765
haftmann@25230
   766
lemma less_add_iff1:
haftmann@25230
   767
  "a * e + c < b * e + d \<longleftrightarrow> (a - b) * e + c < d"
nipkow@29667
   768
by (simp add: algebra_simps)
haftmann@25230
   769
haftmann@25230
   770
lemma less_add_iff2:
haftmann@25230
   771
  "a * e + c < b * e + d \<longleftrightarrow> c < (b - a) * e + d"
nipkow@29667
   772
by (simp add: algebra_simps)
haftmann@25230
   773
haftmann@25230
   774
lemma le_add_iff1:
haftmann@25230
   775
  "a * e + c \<le> b * e + d \<longleftrightarrow> (a - b) * e + c \<le> d"
nipkow@29667
   776
by (simp add: algebra_simps)
haftmann@25230
   777
haftmann@25230
   778
lemma le_add_iff2:
haftmann@25230
   779
  "a * e + c \<le> b * e + d \<longleftrightarrow> c \<le> (b - a) * e + d"
nipkow@29667
   780
by (simp add: algebra_simps)
haftmann@25230
   781
haftmann@25230
   782
lemma mult_left_mono_neg:
haftmann@25230
   783
  "b \<le> a \<Longrightarrow> c \<le> 0 \<Longrightarrow> c * a \<le> c * b"
haftmann@25230
   784
  apply (drule mult_left_mono [of _ _ "uminus c"])
haftmann@25230
   785
  apply (simp_all add: minus_mult_left [symmetric]) 
haftmann@25230
   786
  done
haftmann@25230
   787
haftmann@25230
   788
lemma mult_right_mono_neg:
haftmann@25230
   789
  "b \<le> a \<Longrightarrow> c \<le> 0 \<Longrightarrow> a * c \<le> b * c"
haftmann@25230
   790
  apply (drule mult_right_mono [of _ _ "uminus c"])
haftmann@25230
   791
  apply (simp_all add: minus_mult_right [symmetric]) 
haftmann@25230
   792
  done
haftmann@25230
   793
haftmann@25230
   794
lemma mult_nonpos_nonpos:
haftmann@25230
   795
  "a \<le> 0 \<Longrightarrow> b \<le> 0 \<Longrightarrow> 0 \<le> a * b"
nipkow@29667
   796
by (drule mult_right_mono_neg [of a zero b]) auto
haftmann@25230
   797
haftmann@25230
   798
lemma split_mult_pos_le:
haftmann@25230
   799
  "(0 \<le> a \<and> 0 \<le> b) \<or> (a \<le> 0 \<and> b \<le> 0) \<Longrightarrow> 0 \<le> a * b"
nipkow@29667
   800
by (auto simp add: mult_nonneg_nonneg mult_nonpos_nonpos)
haftmann@25186
   801
haftmann@25186
   802
end
paulson@14270
   803
haftmann@25762
   804
class abs_if = minus + uminus + ord + zero + abs +
haftmann@25762
   805
  assumes abs_if: "\<bar>a\<bar> = (if a < 0 then - a else a)"
haftmann@25762
   806
haftmann@25762
   807
class sgn_if = minus + uminus + zero + one + ord + sgn +
haftmann@25186
   808
  assumes sgn_if: "sgn x = (if x = 0 then 0 else if 0 < x then 1 else - 1)"
nipkow@24506
   809
nipkow@25564
   810
lemma (in sgn_if) sgn0[simp]: "sgn 0 = 0"
nipkow@25564
   811
by(simp add:sgn_if)
nipkow@25564
   812
haftmann@25230
   813
class ordered_ring = ring + ordered_semiring
haftmann@25304
   814
  + ordered_ab_group_add + abs_if
haftmann@25304
   815
begin
haftmann@25304
   816
huffman@27516
   817
subclass pordered_ring ..
haftmann@25304
   818
haftmann@25304
   819
subclass pordered_ab_group_add_abs
haftmann@28823
   820
proof
haftmann@25304
   821
  fix a b
haftmann@25304
   822
  show "\<bar>a + b\<bar> \<le> \<bar>a\<bar> + \<bar>b\<bar>"
nipkow@29667
   823
by (auto simp add: abs_if not_less neg_less_eq_nonneg less_eq_neg_nonpos)
haftmann@25304
   824
   (auto simp del: minus_add_distrib simp add: minus_add_distrib [symmetric]
haftmann@25304
   825
     neg_less_eq_nonneg less_eq_neg_nonpos, auto intro: add_nonneg_nonneg,
haftmann@25304
   826
      auto intro!: less_imp_le add_neg_neg)
haftmann@25304
   827
qed (auto simp add: abs_if less_eq_neg_nonpos neg_equal_zero)
haftmann@25304
   828
haftmann@25304
   829
end
obua@23521
   830
haftmann@25230
   831
(* The "strict" suffix can be seen as describing the combination of ordered_ring and no_zero_divisors.
haftmann@25230
   832
   Basically, ordered_ring + no_zero_divisors = ordered_ring_strict.
haftmann@25230
   833
 *)
haftmann@25230
   834
class ordered_ring_strict = ring + ordered_semiring_strict
haftmann@25304
   835
  + ordered_ab_group_add + abs_if
haftmann@25230
   836
begin
paulson@14348
   837
huffman@27516
   838
subclass ordered_ring ..
haftmann@25304
   839
paulson@14265
   840
lemma mult_strict_left_mono_neg:
haftmann@25230
   841
  "b < a \<Longrightarrow> c < 0 \<Longrightarrow> c * a < c * b"
haftmann@25230
   842
  apply (drule mult_strict_left_mono [of _ _ "uminus c"])
haftmann@25230
   843
  apply (simp_all add: minus_mult_left [symmetric]) 
haftmann@25230
   844
  done
obua@14738
   845
paulson@14265
   846
lemma mult_strict_right_mono_neg:
haftmann@25230
   847
  "b < a \<Longrightarrow> c < 0 \<Longrightarrow> a * c < b * c"
haftmann@25230
   848
  apply (drule mult_strict_right_mono [of _ _ "uminus c"])
haftmann@25230
   849
  apply (simp_all add: minus_mult_right [symmetric]) 
haftmann@25230
   850
  done
obua@14738
   851
haftmann@25230
   852
lemma mult_neg_neg:
haftmann@25230
   853
  "a < 0 \<Longrightarrow> b < 0 \<Longrightarrow> 0 < a * b"
nipkow@29667
   854
by (drule mult_strict_right_mono_neg, auto)
obua@14738
   855
haftmann@25917
   856
subclass ring_no_zero_divisors
haftmann@28823
   857
proof
haftmann@25917
   858
  fix a b
haftmann@25917
   859
  assume "a \<noteq> 0" then have A: "a < 0 \<or> 0 < a" by (simp add: neq_iff)
haftmann@25917
   860
  assume "b \<noteq> 0" then have B: "b < 0 \<or> 0 < b" by (simp add: neq_iff)
haftmann@25917
   861
  have "a * b < 0 \<or> 0 < a * b"
haftmann@25917
   862
  proof (cases "a < 0")
haftmann@25917
   863
    case True note A' = this
haftmann@25917
   864
    show ?thesis proof (cases "b < 0")
haftmann@25917
   865
      case True with A'
haftmann@25917
   866
      show ?thesis by (auto dest: mult_neg_neg)
haftmann@25917
   867
    next
haftmann@25917
   868
      case False with B have "0 < b" by auto
haftmann@25917
   869
      with A' show ?thesis by (auto dest: mult_strict_right_mono)
haftmann@25917
   870
    qed
haftmann@25917
   871
  next
haftmann@25917
   872
    case False with A have A': "0 < a" by auto
haftmann@25917
   873
    show ?thesis proof (cases "b < 0")
haftmann@25917
   874
      case True with A'
haftmann@25917
   875
      show ?thesis by (auto dest: mult_strict_right_mono_neg)
haftmann@25917
   876
    next
haftmann@25917
   877
      case False with B have "0 < b" by auto
haftmann@25917
   878
      with A' show ?thesis by (auto dest: mult_pos_pos)
haftmann@25917
   879
    qed
haftmann@25917
   880
  qed
haftmann@25917
   881
  then show "a * b \<noteq> 0" by (simp add: neq_iff)
haftmann@25917
   882
qed
haftmann@25304
   883
paulson@14265
   884
lemma zero_less_mult_iff:
haftmann@25917
   885
  "0 < a * b \<longleftrightarrow> 0 < a \<and> 0 < b \<or> a < 0 \<and> b < 0"
haftmann@25917
   886
  apply (auto simp add: mult_pos_pos mult_neg_neg)
haftmann@25917
   887
  apply (simp_all add: not_less le_less)
haftmann@25917
   888
  apply (erule disjE) apply assumption defer
haftmann@25917
   889
  apply (erule disjE) defer apply (drule sym) apply simp
haftmann@25917
   890
  apply (erule disjE) defer apply (drule sym) apply simp
haftmann@25917
   891
  apply (erule disjE) apply assumption apply (drule sym) apply simp
haftmann@25917
   892
  apply (drule sym) apply simp
haftmann@25917
   893
  apply (blast dest: zero_less_mult_pos)
haftmann@25230
   894
  apply (blast dest: zero_less_mult_pos2)
haftmann@25230
   895
  done
huffman@22990
   896
paulson@14265
   897
lemma zero_le_mult_iff:
haftmann@25917
   898
  "0 \<le> a * b \<longleftrightarrow> 0 \<le> a \<and> 0 \<le> b \<or> a \<le> 0 \<and> b \<le> 0"
nipkow@29667
   899
by (auto simp add: eq_commute [of 0] le_less not_less zero_less_mult_iff)
paulson@14265
   900
paulson@14265
   901
lemma mult_less_0_iff:
haftmann@25917
   902
  "a * b < 0 \<longleftrightarrow> 0 < a \<and> b < 0 \<or> a < 0 \<and> 0 < b"
haftmann@25917
   903
  apply (insert zero_less_mult_iff [of "-a" b]) 
haftmann@25917
   904
  apply (force simp add: minus_mult_left[symmetric]) 
haftmann@25917
   905
  done
paulson@14265
   906
paulson@14265
   907
lemma mult_le_0_iff:
haftmann@25917
   908
  "a * b \<le> 0 \<longleftrightarrow> 0 \<le> a \<and> b \<le> 0 \<or> a \<le> 0 \<and> 0 \<le> b"
haftmann@25917
   909
  apply (insert zero_le_mult_iff [of "-a" b]) 
haftmann@25917
   910
  apply (force simp add: minus_mult_left[symmetric]) 
haftmann@25917
   911
  done
haftmann@25917
   912
haftmann@25917
   913
lemma zero_le_square [simp]: "0 \<le> a * a"
nipkow@29667
   914
by (simp add: zero_le_mult_iff linear)
haftmann@25917
   915
haftmann@25917
   916
lemma not_square_less_zero [simp]: "\<not> (a * a < 0)"
nipkow@29667
   917
by (simp add: not_less)
haftmann@25917
   918
haftmann@26193
   919
text{*Cancellation laws for @{term "c*a < c*b"} and @{term "a*c < b*c"},
haftmann@26193
   920
   also with the relations @{text "\<le>"} and equality.*}
haftmann@26193
   921
haftmann@26193
   922
text{*These ``disjunction'' versions produce two cases when the comparison is
haftmann@26193
   923
 an assumption, but effectively four when the comparison is a goal.*}
haftmann@26193
   924
haftmann@26193
   925
lemma mult_less_cancel_right_disj:
haftmann@26193
   926
  "a * c < b * c \<longleftrightarrow> 0 < c \<and> a < b \<or> c < 0 \<and>  b < a"
haftmann@26193
   927
  apply (cases "c = 0")
haftmann@26193
   928
  apply (auto simp add: neq_iff mult_strict_right_mono 
haftmann@26193
   929
                      mult_strict_right_mono_neg)
haftmann@26193
   930
  apply (auto simp add: not_less 
haftmann@26193
   931
                      not_le [symmetric, of "a*c"]
haftmann@26193
   932
                      not_le [symmetric, of a])
haftmann@26193
   933
  apply (erule_tac [!] notE)
haftmann@26193
   934
  apply (auto simp add: less_imp_le mult_right_mono 
haftmann@26193
   935
                      mult_right_mono_neg)
haftmann@26193
   936
  done
haftmann@26193
   937
haftmann@26193
   938
lemma mult_less_cancel_left_disj:
haftmann@26193
   939
  "c * a < c * b \<longleftrightarrow> 0 < c \<and> a < b \<or> c < 0 \<and>  b < a"
haftmann@26193
   940
  apply (cases "c = 0")
haftmann@26193
   941
  apply (auto simp add: neq_iff mult_strict_left_mono 
haftmann@26193
   942
                      mult_strict_left_mono_neg)
haftmann@26193
   943
  apply (auto simp add: not_less 
haftmann@26193
   944
                      not_le [symmetric, of "c*a"]
haftmann@26193
   945
                      not_le [symmetric, of a])
haftmann@26193
   946
  apply (erule_tac [!] notE)
haftmann@26193
   947
  apply (auto simp add: less_imp_le mult_left_mono 
haftmann@26193
   948
                      mult_left_mono_neg)
haftmann@26193
   949
  done
haftmann@26193
   950
haftmann@26193
   951
text{*The ``conjunction of implication'' lemmas produce two cases when the
haftmann@26193
   952
comparison is a goal, but give four when the comparison is an assumption.*}
haftmann@26193
   953
haftmann@26193
   954
lemma mult_less_cancel_right:
haftmann@26193
   955
  "a * c < b * c \<longleftrightarrow> (0 \<le> c \<longrightarrow> a < b) \<and> (c \<le> 0 \<longrightarrow> b < a)"
haftmann@26193
   956
  using mult_less_cancel_right_disj [of a c b] by auto
haftmann@26193
   957
haftmann@26193
   958
lemma mult_less_cancel_left:
haftmann@26193
   959
  "c * a < c * b \<longleftrightarrow> (0 \<le> c \<longrightarrow> a < b) \<and> (c \<le> 0 \<longrightarrow> b < a)"
haftmann@26193
   960
  using mult_less_cancel_left_disj [of c a b] by auto
haftmann@26193
   961
haftmann@26193
   962
lemma mult_le_cancel_right:
haftmann@26193
   963
   "a * c \<le> b * c \<longleftrightarrow> (0 < c \<longrightarrow> a \<le> b) \<and> (c < 0 \<longrightarrow> b \<le> a)"
nipkow@29667
   964
by (simp add: not_less [symmetric] mult_less_cancel_right_disj)
haftmann@26193
   965
haftmann@26193
   966
lemma mult_le_cancel_left:
haftmann@26193
   967
  "c * a \<le> c * b \<longleftrightarrow> (0 < c \<longrightarrow> a \<le> b) \<and> (c < 0 \<longrightarrow> b \<le> a)"
nipkow@29667
   968
by (simp add: not_less [symmetric] mult_less_cancel_left_disj)
haftmann@26193
   969
haftmann@25917
   970
end
paulson@14265
   971
nipkow@29667
   972
text{*Legacy - use @{text algebra_simps} *}
nipkow@29833
   973
lemmas ring_simps[noatp] = algebra_simps
haftmann@25230
   974
haftmann@25230
   975
haftmann@25230
   976
class pordered_comm_ring = comm_ring + pordered_comm_semiring
haftmann@25267
   977
begin
haftmann@25230
   978
huffman@27516
   979
subclass pordered_ring ..
huffman@27516
   980
subclass pordered_cancel_comm_semiring ..
haftmann@25230
   981
haftmann@25267
   982
end
haftmann@25230
   983
haftmann@25230
   984
class ordered_semidom = comm_semiring_1_cancel + ordered_comm_semiring_strict +
haftmann@25230
   985
  (*previously ordered_semiring*)
haftmann@25230
   986
  assumes zero_less_one [simp]: "0 < 1"
haftmann@25230
   987
begin
haftmann@25230
   988
haftmann@25230
   989
lemma pos_add_strict:
haftmann@25230
   990
  shows "0 < a \<Longrightarrow> b < c \<Longrightarrow> b < a + c"
haftmann@25230
   991
  using add_strict_mono [of zero a b c] by simp
haftmann@25230
   992
haftmann@26193
   993
lemma zero_le_one [simp]: "0 \<le> 1"
nipkow@29667
   994
by (rule zero_less_one [THEN less_imp_le]) 
haftmann@26193
   995
haftmann@26193
   996
lemma not_one_le_zero [simp]: "\<not> 1 \<le> 0"
nipkow@29667
   997
by (simp add: not_le) 
haftmann@26193
   998
haftmann@26193
   999
lemma not_one_less_zero [simp]: "\<not> 1 < 0"
nipkow@29667
  1000
by (simp add: not_less) 
haftmann@26193
  1001
haftmann@26193
  1002
lemma less_1_mult:
haftmann@26193
  1003
  assumes "1 < m" and "1 < n"
haftmann@26193
  1004
  shows "1 < m * n"
haftmann@26193
  1005
  using assms mult_strict_mono [of 1 m 1 n]
haftmann@26193
  1006
    by (simp add:  less_trans [OF zero_less_one]) 
haftmann@26193
  1007
haftmann@25230
  1008
end
haftmann@25230
  1009
haftmann@26193
  1010
class ordered_idom = comm_ring_1 +
haftmann@26193
  1011
  ordered_comm_semiring_strict + ordered_ab_group_add +
haftmann@25230
  1012
  abs_if + sgn_if
haftmann@25230
  1013
  (*previously ordered_ring*)
haftmann@25917
  1014
begin
haftmann@25917
  1015
huffman@27516
  1016
subclass ordered_ring_strict ..
huffman@27516
  1017
subclass pordered_comm_ring ..
huffman@27516
  1018
subclass idom ..
haftmann@25917
  1019
haftmann@25917
  1020
subclass ordered_semidom
haftmann@28823
  1021
proof
haftmann@26193
  1022
  have "0 \<le> 1 * 1" by (rule zero_le_square)
haftmann@26193
  1023
  thus "0 < 1" by (simp add: le_less)
haftmann@25917
  1024
qed 
haftmann@25917
  1025
haftmann@26193
  1026
lemma linorder_neqE_ordered_idom:
haftmann@26193
  1027
  assumes "x \<noteq> y" obtains "x < y" | "y < x"
haftmann@26193
  1028
  using assms by (rule neqE)
haftmann@26193
  1029
haftmann@26274
  1030
text {* These cancellation simprules also produce two cases when the comparison is a goal. *}
haftmann@26274
  1031
haftmann@26274
  1032
lemma mult_le_cancel_right1:
haftmann@26274
  1033
  "c \<le> b * c \<longleftrightarrow> (0 < c \<longrightarrow> 1 \<le> b) \<and> (c < 0 \<longrightarrow> b \<le> 1)"
nipkow@29667
  1034
by (insert mult_le_cancel_right [of 1 c b], simp)
haftmann@26274
  1035
haftmann@26274
  1036
lemma mult_le_cancel_right2:
haftmann@26274
  1037
  "a * c \<le> c \<longleftrightarrow> (0 < c \<longrightarrow> a \<le> 1) \<and> (c < 0 \<longrightarrow> 1 \<le> a)"
nipkow@29667
  1038
by (insert mult_le_cancel_right [of a c 1], simp)
haftmann@26274
  1039
haftmann@26274
  1040
lemma mult_le_cancel_left1:
haftmann@26274
  1041
  "c \<le> c * b \<longleftrightarrow> (0 < c \<longrightarrow> 1 \<le> b) \<and> (c < 0 \<longrightarrow> b \<le> 1)"
nipkow@29667
  1042
by (insert mult_le_cancel_left [of c 1 b], simp)
haftmann@26274
  1043
haftmann@26274
  1044
lemma mult_le_cancel_left2:
haftmann@26274
  1045
  "c * a \<le> c \<longleftrightarrow> (0 < c \<longrightarrow> a \<le> 1) \<and> (c < 0 \<longrightarrow> 1 \<le> a)"
nipkow@29667
  1046
by (insert mult_le_cancel_left [of c a 1], simp)
haftmann@26274
  1047
haftmann@26274
  1048
lemma mult_less_cancel_right1:
haftmann@26274
  1049
  "c < b * c \<longleftrightarrow> (0 \<le> c \<longrightarrow> 1 < b) \<and> (c \<le> 0 \<longrightarrow> b < 1)"
nipkow@29667
  1050
by (insert mult_less_cancel_right [of 1 c b], simp)
haftmann@26274
  1051
haftmann@26274
  1052
lemma mult_less_cancel_right2:
haftmann@26274
  1053
  "a * c < c \<longleftrightarrow> (0 \<le> c \<longrightarrow> a < 1) \<and> (c \<le> 0 \<longrightarrow> 1 < a)"
nipkow@29667
  1054
by (insert mult_less_cancel_right [of a c 1], simp)
haftmann@26274
  1055
haftmann@26274
  1056
lemma mult_less_cancel_left1:
haftmann@26274
  1057
  "c < c * b \<longleftrightarrow> (0 \<le> c \<longrightarrow> 1 < b) \<and> (c \<le> 0 \<longrightarrow> b < 1)"
nipkow@29667
  1058
by (insert mult_less_cancel_left [of c 1 b], simp)
haftmann@26274
  1059
haftmann@26274
  1060
lemma mult_less_cancel_left2:
haftmann@26274
  1061
  "c * a < c \<longleftrightarrow> (0 \<le> c \<longrightarrow> a < 1) \<and> (c \<le> 0 \<longrightarrow> 1 < a)"
nipkow@29667
  1062
by (insert mult_less_cancel_left [of c a 1], simp)
haftmann@26274
  1063
haftmann@27651
  1064
lemma sgn_sgn [simp]:
haftmann@27651
  1065
  "sgn (sgn a) = sgn a"
nipkow@29700
  1066
unfolding sgn_if by simp
haftmann@27651
  1067
haftmann@27651
  1068
lemma sgn_0_0:
haftmann@27651
  1069
  "sgn a = 0 \<longleftrightarrow> a = 0"
nipkow@29700
  1070
unfolding sgn_if by simp
haftmann@27651
  1071
haftmann@27651
  1072
lemma sgn_1_pos:
haftmann@27651
  1073
  "sgn a = 1 \<longleftrightarrow> a > 0"
nipkow@29700
  1074
unfolding sgn_if by (simp add: neg_equal_zero)
haftmann@27651
  1075
haftmann@27651
  1076
lemma sgn_1_neg:
haftmann@27651
  1077
  "sgn a = - 1 \<longleftrightarrow> a < 0"
nipkow@29700
  1078
unfolding sgn_if by (auto simp add: equal_neg_zero)
haftmann@27651
  1079
haftmann@29940
  1080
lemma sgn_pos [simp]:
haftmann@29940
  1081
  "0 < a \<Longrightarrow> sgn a = 1"
haftmann@29940
  1082
unfolding sgn_1_pos .
haftmann@29940
  1083
haftmann@29940
  1084
lemma sgn_neg [simp]:
haftmann@29940
  1085
  "a < 0 \<Longrightarrow> sgn a = - 1"
haftmann@29940
  1086
unfolding sgn_1_neg .
haftmann@29940
  1087
haftmann@27651
  1088
lemma sgn_times:
haftmann@27651
  1089
  "sgn (a * b) = sgn a * sgn b"
nipkow@29667
  1090
by (auto simp add: sgn_if zero_less_mult_iff)
haftmann@27651
  1091
haftmann@29653
  1092
lemma abs_sgn: "abs k = k * sgn k"
nipkow@29700
  1093
unfolding sgn_if abs_if by auto
nipkow@29700
  1094
haftmann@29940
  1095
lemma sgn_greater [simp]:
haftmann@29940
  1096
  "0 < sgn a \<longleftrightarrow> 0 < a"
haftmann@29940
  1097
  unfolding sgn_if by auto
haftmann@29940
  1098
haftmann@29940
  1099
lemma sgn_less [simp]:
haftmann@29940
  1100
  "sgn a < 0 \<longleftrightarrow> a < 0"
haftmann@29940
  1101
  unfolding sgn_if by auto
haftmann@29940
  1102
huffman@29949
  1103
lemma abs_dvd_iff [simp]: "(abs m) dvd k \<longleftrightarrow> m dvd k"
huffman@29949
  1104
  by (simp add: abs_if)
huffman@29949
  1105
huffman@29949
  1106
lemma dvd_abs_iff [simp]: "m dvd (abs k) \<longleftrightarrow> m dvd k"
huffman@29949
  1107
  by (simp add: abs_if)
haftmann@29653
  1108
haftmann@25917
  1109
end
haftmann@25230
  1110
haftmann@25230
  1111
class ordered_field = field + ordered_idom
haftmann@25230
  1112
haftmann@26274
  1113
text {* Simprules for comparisons where common factors can be cancelled. *}
paulson@15234
  1114
nipkow@29833
  1115
lemmas mult_compare_simps[noatp] =
paulson@15234
  1116
    mult_le_cancel_right mult_le_cancel_left
paulson@15234
  1117
    mult_le_cancel_right1 mult_le_cancel_right2
paulson@15234
  1118
    mult_le_cancel_left1 mult_le_cancel_left2
paulson@15234
  1119
    mult_less_cancel_right mult_less_cancel_left
paulson@15234
  1120
    mult_less_cancel_right1 mult_less_cancel_right2
paulson@15234
  1121
    mult_less_cancel_left1 mult_less_cancel_left2
paulson@15234
  1122
    mult_cancel_right mult_cancel_left
paulson@15234
  1123
    mult_cancel_right1 mult_cancel_right2
paulson@15234
  1124
    mult_cancel_left1 mult_cancel_left2
paulson@15234
  1125
haftmann@26274
  1126
-- {* FIXME continue localization here *}
paulson@14268
  1127
paulson@14268
  1128
lemma inverse_nonzero_iff_nonzero [simp]:
huffman@20496
  1129
   "(inverse a = 0) = (a = (0::'a::{division_ring,division_by_zero}))"
haftmann@26274
  1130
by (force dest: inverse_zero_imp_zero) 
paulson@14268
  1131
paulson@14268
  1132
lemma inverse_minus_eq [simp]:
huffman@20496
  1133
   "inverse(-a) = -inverse(a::'a::{division_ring,division_by_zero})"
paulson@14377
  1134
proof cases
paulson@14377
  1135
  assume "a=0" thus ?thesis by (simp add: inverse_zero)
paulson@14377
  1136
next
paulson@14377
  1137
  assume "a\<noteq>0" 
paulson@14377
  1138
  thus ?thesis by (simp add: nonzero_inverse_minus_eq)
paulson@14377
  1139
qed
paulson@14268
  1140
paulson@14268
  1141
lemma inverse_eq_imp_eq:
huffman@20496
  1142
  "inverse a = inverse b ==> a = (b::'a::{division_ring,division_by_zero})"
haftmann@21328
  1143
apply (cases "a=0 | b=0") 
paulson@14268
  1144
 apply (force dest!: inverse_zero_imp_zero
paulson@14268
  1145
              simp add: eq_commute [of "0::'a"])
paulson@14268
  1146
apply (force dest!: nonzero_inverse_eq_imp_eq) 
paulson@14268
  1147
done
paulson@14268
  1148
paulson@14268
  1149
lemma inverse_eq_iff_eq [simp]:
huffman@20496
  1150
  "(inverse a = inverse b) = (a = (b::'a::{division_ring,division_by_zero}))"
huffman@20496
  1151
by (force dest!: inverse_eq_imp_eq)
paulson@14268
  1152
paulson@14270
  1153
lemma inverse_inverse_eq [simp]:
huffman@20496
  1154
     "inverse(inverse (a::'a::{division_ring,division_by_zero})) = a"
paulson@14270
  1155
  proof cases
paulson@14270
  1156
    assume "a=0" thus ?thesis by simp
paulson@14270
  1157
  next
paulson@14270
  1158
    assume "a\<noteq>0" 
paulson@14270
  1159
    thus ?thesis by (simp add: nonzero_inverse_inverse_eq)
paulson@14270
  1160
  qed
paulson@14270
  1161
paulson@14270
  1162
text{*This version builds in division by zero while also re-orienting
paulson@14270
  1163
      the right-hand side.*}
paulson@14270
  1164
lemma inverse_mult_distrib [simp]:
paulson@14270
  1165
     "inverse(a*b) = inverse(a) * inverse(b::'a::{field,division_by_zero})"
paulson@14270
  1166
  proof cases
paulson@14270
  1167
    assume "a \<noteq> 0 & b \<noteq> 0" 
nipkow@29667
  1168
    thus ?thesis by (simp add: nonzero_inverse_mult_distrib mult_commute)
paulson@14270
  1169
  next
paulson@14270
  1170
    assume "~ (a \<noteq> 0 & b \<noteq> 0)" 
nipkow@29667
  1171
    thus ?thesis by force
paulson@14270
  1172
  qed
paulson@14270
  1173
paulson@14270
  1174
text{*There is no slick version using division by zero.*}
paulson@14270
  1175
lemma inverse_add:
nipkow@23477
  1176
  "[|a \<noteq> 0;  b \<noteq> 0|]
nipkow@23477
  1177
   ==> inverse a + inverse b = (a+b) * inverse a * inverse (b::'a::field)"
huffman@20496
  1178
by (simp add: division_ring_inverse_add mult_ac)
paulson@14270
  1179
paulson@14365
  1180
lemma inverse_divide [simp]:
nipkow@23477
  1181
  "inverse (a/b) = b / (a::'a::{field,division_by_zero})"
nipkow@23477
  1182
by (simp add: divide_inverse mult_commute)
paulson@14365
  1183
wenzelm@23389
  1184
avigad@16775
  1185
subsection {* Calculations with fractions *}
avigad@16775
  1186
nipkow@23413
  1187
text{* There is a whole bunch of simp-rules just for class @{text
nipkow@23413
  1188
field} but none for class @{text field} and @{text nonzero_divides}
nipkow@23413
  1189
because the latter are covered by a simproc. *}
nipkow@23413
  1190
paulson@24427
  1191
lemma nonzero_mult_divide_mult_cancel_left[simp,noatp]:
nipkow@23477
  1192
assumes [simp]: "b\<noteq>0" and [simp]: "c\<noteq>0" shows "(c*a)/(c*b) = a/(b::'a::field)"
paulson@14277
  1193
proof -
paulson@14277
  1194
  have "(c*a)/(c*b) = c * a * (inverse b * inverse c)"
nipkow@23482
  1195
    by (simp add: divide_inverse nonzero_inverse_mult_distrib)
paulson@14277
  1196
  also have "... =  a * inverse b * (inverse c * c)"
paulson@14277
  1197
    by (simp only: mult_ac)
nipkow@29667
  1198
  also have "... =  a * inverse b" by simp
nipkow@29667
  1199
    finally show ?thesis by (simp add: divide_inverse)
paulson@14277
  1200
qed
paulson@14277
  1201
nipkow@23413
  1202
lemma mult_divide_mult_cancel_left:
nipkow@23477
  1203
  "c\<noteq>0 ==> (c*a) / (c*b) = a / (b::'a::{field,division_by_zero})"
haftmann@21328
  1204
apply (cases "b = 0")
nipkow@23413
  1205
apply (simp_all add: nonzero_mult_divide_mult_cancel_left)
paulson@14277
  1206
done
paulson@14277
  1207
paulson@24427
  1208
lemma nonzero_mult_divide_mult_cancel_right [noatp]:
nipkow@23477
  1209
  "[|b\<noteq>0; c\<noteq>0|] ==> (a*c) / (b*c) = a/(b::'a::field)"
nipkow@23413
  1210
by (simp add: mult_commute [of _ c] nonzero_mult_divide_mult_cancel_left) 
paulson@14321
  1211
nipkow@23413
  1212
lemma mult_divide_mult_cancel_right:
nipkow@23477
  1213
  "c\<noteq>0 ==> (a*c) / (b*c) = a / (b::'a::{field,division_by_zero})"
haftmann@21328
  1214
apply (cases "b = 0")
nipkow@23413
  1215
apply (simp_all add: nonzero_mult_divide_mult_cancel_right)
paulson@14321
  1216
done
nipkow@23413
  1217
paulson@14284
  1218
lemma divide_1 [simp]: "a/1 = (a::'a::field)"
nipkow@23477
  1219
by (simp add: divide_inverse)
paulson@14284
  1220
paulson@15234
  1221
lemma times_divide_eq_right: "a * (b/c) = (a*b) / (c::'a::field)"
paulson@14430
  1222
by (simp add: divide_inverse mult_assoc)
paulson@14288
  1223
paulson@14430
  1224
lemma times_divide_eq_left: "(b/c) * a = (b*a) / (c::'a::field)"
paulson@14430
  1225
by (simp add: divide_inverse mult_ac)
paulson@14288
  1226
nipkow@29833
  1227
lemmas times_divide_eq[noatp] = times_divide_eq_right times_divide_eq_left
nipkow@23482
  1228
paulson@24286
  1229
lemma divide_divide_eq_right [simp,noatp]:
nipkow@23477
  1230
  "a / (b/c) = (a*c) / (b::'a::{field,division_by_zero})"
paulson@14430
  1231
by (simp add: divide_inverse mult_ac)
paulson@14288
  1232
paulson@24286
  1233
lemma divide_divide_eq_left [simp,noatp]:
nipkow@23477
  1234
  "(a / b) / (c::'a::{field,division_by_zero}) = a / (b*c)"
paulson@14430
  1235
by (simp add: divide_inverse mult_assoc)
paulson@14288
  1236
avigad@16775
  1237
lemma add_frac_eq: "(y::'a::field) ~= 0 ==> z ~= 0 ==>
avigad@16775
  1238
    x / y + w / z = (x * z + w * y) / (y * z)"
nipkow@23477
  1239
apply (subgoal_tac "x / y = (x * z) / (y * z)")
nipkow@23477
  1240
apply (erule ssubst)
nipkow@23477
  1241
apply (subgoal_tac "w / z = (w * y) / (y * z)")
nipkow@23477
  1242
apply (erule ssubst)
nipkow@23477
  1243
apply (rule add_divide_distrib [THEN sym])
nipkow@23477
  1244
apply (subst mult_commute)
nipkow@23477
  1245
apply (erule nonzero_mult_divide_mult_cancel_left [THEN sym])
nipkow@23477
  1246
apply assumption
nipkow@23477
  1247
apply (erule nonzero_mult_divide_mult_cancel_right [THEN sym])
nipkow@23477
  1248
apply assumption
avigad@16775
  1249
done
paulson@14268
  1250
wenzelm@23389
  1251
paulson@15234
  1252
subsubsection{*Special Cancellation Simprules for Division*}
paulson@15234
  1253
paulson@24427
  1254
lemma mult_divide_mult_cancel_left_if[simp,noatp]:
nipkow@23477
  1255
fixes c :: "'a :: {field,division_by_zero}"
nipkow@23477
  1256
shows "(c*a) / (c*b) = (if c=0 then 0 else a/b)"
nipkow@23413
  1257
by (simp add: mult_divide_mult_cancel_left)
nipkow@23413
  1258
paulson@24427
  1259
lemma nonzero_mult_divide_cancel_right[simp,noatp]:
nipkow@23413
  1260
  "b \<noteq> 0 \<Longrightarrow> a * b / b = (a::'a::field)"
nipkow@23413
  1261
using nonzero_mult_divide_mult_cancel_right[of 1 b a] by simp
nipkow@23413
  1262
paulson@24427
  1263
lemma nonzero_mult_divide_cancel_left[simp,noatp]:
nipkow@23413
  1264
  "a \<noteq> 0 \<Longrightarrow> a * b / a = (b::'a::field)"
nipkow@23413
  1265
using nonzero_mult_divide_mult_cancel_left[of 1 a b] by simp
nipkow@23413
  1266
nipkow@23413
  1267
paulson@24427
  1268
lemma nonzero_divide_mult_cancel_right[simp,noatp]:
nipkow@23413
  1269
  "\<lbrakk> a\<noteq>0; b\<noteq>0 \<rbrakk> \<Longrightarrow> b / (a * b) = 1/(a::'a::field)"
nipkow@23413
  1270
using nonzero_mult_divide_mult_cancel_right[of a b 1] by simp
nipkow@23413
  1271
paulson@24427
  1272
lemma nonzero_divide_mult_cancel_left[simp,noatp]:
nipkow@23413
  1273
  "\<lbrakk> a\<noteq>0; b\<noteq>0 \<rbrakk> \<Longrightarrow> a / (a * b) = 1/(b::'a::field)"
nipkow@23413
  1274
using nonzero_mult_divide_mult_cancel_left[of b a 1] by simp
nipkow@23413
  1275
nipkow@23413
  1276
paulson@24427
  1277
lemma nonzero_mult_divide_mult_cancel_left2[simp,noatp]:
nipkow@23477
  1278
  "[|b\<noteq>0; c\<noteq>0|] ==> (c*a) / (b*c) = a/(b::'a::field)"
nipkow@23413
  1279
using nonzero_mult_divide_mult_cancel_left[of b c a] by(simp add:mult_ac)
nipkow@23413
  1280
paulson@24427
  1281
lemma nonzero_mult_divide_mult_cancel_right2[simp,noatp]:
nipkow@23477
  1282
  "[|b\<noteq>0; c\<noteq>0|] ==> (a*c) / (c*b) = a/(b::'a::field)"
nipkow@23413
  1283
using nonzero_mult_divide_mult_cancel_right[of b c a] by(simp add:mult_ac)
nipkow@23413
  1284
paulson@15234
  1285
paulson@14293
  1286
subsection {* Division and Unary Minus *}
paulson@14293
  1287
paulson@14293
  1288
lemma nonzero_minus_divide_left: "b \<noteq> 0 ==> - (a/b) = (-a) / (b::'a::field)"
huffman@29407
  1289
by (simp add: divide_inverse)
paulson@14293
  1290
paulson@14293
  1291
lemma nonzero_minus_divide_right: "b \<noteq> 0 ==> - (a/b) = a / -(b::'a::field)"
huffman@29407
  1292
by (simp add: divide_inverse nonzero_inverse_minus_eq)
paulson@14293
  1293
paulson@14293
  1294
lemma nonzero_minus_divide_divide: "b \<noteq> 0 ==> (-a)/(-b) = a / (b::'a::field)"
paulson@14293
  1295
by (simp add: divide_inverse nonzero_inverse_minus_eq)
paulson@14293
  1296
paulson@14430
  1297
lemma minus_divide_left: "- (a/b) = (-a) / (b::'a::field)"
huffman@29407
  1298
by (simp add: divide_inverse)
paulson@14293
  1299
paulson@14293
  1300
lemma minus_divide_right: "- (a/b) = a / -(b::'a::{field,division_by_zero})"
huffman@29407
  1301
by (simp add: divide_inverse)
paulson@14430
  1302
paulson@14293
  1303
paulson@14293
  1304
text{*The effect is to extract signs from divisions*}
nipkow@29833
  1305
lemmas divide_minus_left[noatp] = minus_divide_left [symmetric]
nipkow@29833
  1306
lemmas divide_minus_right[noatp] = minus_divide_right [symmetric]
paulson@17085
  1307
declare divide_minus_left [simp]   divide_minus_right [simp]
paulson@14293
  1308
paulson@14293
  1309
lemma minus_divide_divide [simp]:
nipkow@23477
  1310
  "(-a)/(-b) = a / (b::'a::{field,division_by_zero})"
haftmann@21328
  1311
apply (cases "b=0", simp) 
paulson@14293
  1312
apply (simp add: nonzero_minus_divide_divide) 
paulson@14293
  1313
done
paulson@14293
  1314
paulson@14430
  1315
lemma diff_divide_distrib: "(a-b)/(c::'a::field) = a/c - b/c"
paulson@14387
  1316
by (simp add: diff_minus add_divide_distrib) 
paulson@14387
  1317
nipkow@23482
  1318
lemma add_divide_eq_iff:
nipkow@23482
  1319
  "(z::'a::field) \<noteq> 0 \<Longrightarrow> x + y/z = (z*x + y)/z"
nipkow@23482
  1320
by(simp add:add_divide_distrib nonzero_mult_divide_cancel_left)
nipkow@23482
  1321
nipkow@23482
  1322
lemma divide_add_eq_iff:
nipkow@23482
  1323
  "(z::'a::field) \<noteq> 0 \<Longrightarrow> x/z + y = (x + z*y)/z"
nipkow@23482
  1324
by(simp add:add_divide_distrib nonzero_mult_divide_cancel_left)
nipkow@23482
  1325
nipkow@23482
  1326
lemma diff_divide_eq_iff:
nipkow@23482
  1327
  "(z::'a::field) \<noteq> 0 \<Longrightarrow> x - y/z = (z*x - y)/z"
nipkow@23482
  1328
by(simp add:diff_divide_distrib nonzero_mult_divide_cancel_left)
nipkow@23482
  1329
nipkow@23482
  1330
lemma divide_diff_eq_iff:
nipkow@23482
  1331
  "(z::'a::field) \<noteq> 0 \<Longrightarrow> x/z - y = (x - z*y)/z"
nipkow@23482
  1332
by(simp add:diff_divide_distrib nonzero_mult_divide_cancel_left)
nipkow@23482
  1333
nipkow@23482
  1334
lemma nonzero_eq_divide_eq: "c\<noteq>0 ==> ((a::'a::field) = b/c) = (a*c = b)"
nipkow@23482
  1335
proof -
nipkow@23482
  1336
  assume [simp]: "c\<noteq>0"
nipkow@23496
  1337
  have "(a = b/c) = (a*c = (b/c)*c)" by simp
nipkow@23496
  1338
  also have "... = (a*c = b)" by (simp add: divide_inverse mult_assoc)
nipkow@23482
  1339
  finally show ?thesis .
nipkow@23482
  1340
qed
nipkow@23482
  1341
nipkow@23482
  1342
lemma nonzero_divide_eq_eq: "c\<noteq>0 ==> (b/c = (a::'a::field)) = (b = a*c)"
nipkow@23482
  1343
proof -
nipkow@23482
  1344
  assume [simp]: "c\<noteq>0"
nipkow@23496
  1345
  have "(b/c = a) = ((b/c)*c = a*c)"  by simp
nipkow@23496
  1346
  also have "... = (b = a*c)"  by (simp add: divide_inverse mult_assoc) 
nipkow@23482
  1347
  finally show ?thesis .
nipkow@23482
  1348
qed
nipkow@23482
  1349
nipkow@23482
  1350
lemma eq_divide_eq:
nipkow@23482
  1351
  "((a::'a::{field,division_by_zero}) = b/c) = (if c\<noteq>0 then a*c = b else a=0)"
nipkow@23482
  1352
by (simp add: nonzero_eq_divide_eq) 
nipkow@23482
  1353
nipkow@23482
  1354
lemma divide_eq_eq:
nipkow@23482
  1355
  "(b/c = (a::'a::{field,division_by_zero})) = (if c\<noteq>0 then b = a*c else a=0)"
nipkow@23482
  1356
by (force simp add: nonzero_divide_eq_eq) 
nipkow@23482
  1357
nipkow@23482
  1358
lemma divide_eq_imp: "(c::'a::{division_by_zero,field}) ~= 0 ==>
nipkow@23482
  1359
    b = a * c ==> b / c = a"
nipkow@29667
  1360
by (subst divide_eq_eq, simp)
nipkow@23482
  1361
nipkow@23482
  1362
lemma eq_divide_imp: "(c::'a::{division_by_zero,field}) ~= 0 ==>
nipkow@23482
  1363
    a * c = b ==> a = b / c"
nipkow@29667
  1364
by (subst eq_divide_eq, simp)
nipkow@29667
  1365
nipkow@29667
  1366
nipkow@29833
  1367
lemmas field_eq_simps[noatp] = algebra_simps
nipkow@23482
  1368
  (* pull / out*)
nipkow@23482
  1369
  add_divide_eq_iff divide_add_eq_iff
nipkow@23482
  1370
  diff_divide_eq_iff divide_diff_eq_iff
nipkow@23482
  1371
  (* multiply eqn *)
nipkow@23482
  1372
  nonzero_eq_divide_eq nonzero_divide_eq_eq
nipkow@23482
  1373
(* is added later:
nipkow@23482
  1374
  times_divide_eq_left times_divide_eq_right
nipkow@23482
  1375
*)
nipkow@23482
  1376
nipkow@23482
  1377
text{*An example:*}
nipkow@23482
  1378
lemma fixes a b c d e f :: "'a::field"
nipkow@23482
  1379
shows "\<lbrakk>a\<noteq>b; c\<noteq>d; e\<noteq>f \<rbrakk> \<Longrightarrow> ((a-b)*(c-d)*(e-f))/((c-d)*(e-f)*(a-b)) = 1"
nipkow@23482
  1380
apply(subgoal_tac "(c-d)*(e-f)*(a-b) \<noteq> 0")
nipkow@23482
  1381
 apply(simp add:field_eq_simps)
nipkow@23482
  1382
apply(simp)
nipkow@23482
  1383
done
nipkow@23482
  1384
nipkow@23482
  1385
avigad@16775
  1386
lemma diff_frac_eq: "(y::'a::field) ~= 0 ==> z ~= 0 ==>
avigad@16775
  1387
    x / y - w / z = (x * z - w * y) / (y * z)"
nipkow@23482
  1388
by (simp add:field_eq_simps times_divide_eq)
nipkow@23482
  1389
nipkow@23482
  1390
lemma frac_eq_eq: "(y::'a::field) ~= 0 ==> z ~= 0 ==>
nipkow@23482
  1391
    (x / y = w / z) = (x * z = w * y)"
nipkow@23482
  1392
by (simp add:field_eq_simps times_divide_eq)
paulson@14293
  1393
wenzelm@23389
  1394
paulson@14268
  1395
subsection {* Ordered Fields *}
paulson@14268
  1396
paulson@14277
  1397
lemma positive_imp_inverse_positive: 
nipkow@23482
  1398
assumes a_gt_0: "0 < a"  shows "0 < inverse (a::'a::ordered_field)"
nipkow@23482
  1399
proof -
paulson@14268
  1400
  have "0 < a * inverse a" 
paulson@14268
  1401
    by (simp add: a_gt_0 [THEN order_less_imp_not_eq2] zero_less_one)
paulson@14268
  1402
  thus "0 < inverse a" 
paulson@14268
  1403
    by (simp add: a_gt_0 [THEN order_less_not_sym] zero_less_mult_iff)
nipkow@23482
  1404
qed
paulson@14268
  1405
paulson@14277
  1406
lemma negative_imp_inverse_negative:
nipkow@23482
  1407
  "a < 0 ==> inverse a < (0::'a::ordered_field)"
nipkow@23482
  1408
by (insert positive_imp_inverse_positive [of "-a"], 
nipkow@23482
  1409
    simp add: nonzero_inverse_minus_eq order_less_imp_not_eq)
paulson@14268
  1410
paulson@14268
  1411
lemma inverse_le_imp_le:
nipkow@23482
  1412
assumes invle: "inverse a \<le> inverse b" and apos:  "0 < a"
nipkow@23482
  1413
shows "b \<le> (a::'a::ordered_field)"
nipkow@23482
  1414
proof (rule classical)
paulson@14268
  1415
  assume "~ b \<le> a"
nipkow@23482
  1416
  hence "a < b"  by (simp add: linorder_not_le)
nipkow@23482
  1417
  hence bpos: "0 < b"  by (blast intro: apos order_less_trans)
paulson@14268
  1418
  hence "a * inverse a \<le> a * inverse b"
paulson@14268
  1419
    by (simp add: apos invle order_less_imp_le mult_left_mono)
paulson@14268
  1420
  hence "(a * inverse a) * b \<le> (a * inverse b) * b"
paulson@14268
  1421
    by (simp add: bpos order_less_imp_le mult_right_mono)
nipkow@23482
  1422
  thus "b \<le> a"  by (simp add: mult_assoc apos bpos order_less_imp_not_eq2)
nipkow@23482
  1423
qed
paulson@14268
  1424
paulson@14277
  1425
lemma inverse_positive_imp_positive:
nipkow@23482
  1426
assumes inv_gt_0: "0 < inverse a" and nz: "a \<noteq> 0"
nipkow@23482
  1427
shows "0 < (a::'a::ordered_field)"
wenzelm@23389
  1428
proof -
paulson@14277
  1429
  have "0 < inverse (inverse a)"
wenzelm@23389
  1430
    using inv_gt_0 by (rule positive_imp_inverse_positive)
paulson@14277
  1431
  thus "0 < a"
wenzelm@23389
  1432
    using nz by (simp add: nonzero_inverse_inverse_eq)
wenzelm@23389
  1433
qed
paulson@14277
  1434
paulson@14277
  1435
lemma inverse_positive_iff_positive [simp]:
nipkow@23482
  1436
  "(0 < inverse a) = (0 < (a::'a::{ordered_field,division_by_zero}))"
haftmann@21328
  1437
apply (cases "a = 0", simp)
paulson@14277
  1438
apply (blast intro: inverse_positive_imp_positive positive_imp_inverse_positive)
paulson@14277
  1439
done
paulson@14277
  1440
paulson@14277
  1441
lemma inverse_negative_imp_negative:
nipkow@23482
  1442
assumes inv_less_0: "inverse a < 0" and nz:  "a \<noteq> 0"
nipkow@23482
  1443
shows "a < (0::'a::ordered_field)"
wenzelm@23389
  1444
proof -
paulson@14277
  1445
  have "inverse (inverse a) < 0"
wenzelm@23389
  1446
    using inv_less_0 by (rule negative_imp_inverse_negative)
nipkow@23482
  1447
  thus "a < 0" using nz by (simp add: nonzero_inverse_inverse_eq)
wenzelm@23389
  1448
qed
paulson@14277
  1449
paulson@14277
  1450
lemma inverse_negative_iff_negative [simp]:
nipkow@23482
  1451
  "(inverse a < 0) = (a < (0::'a::{ordered_field,division_by_zero}))"
haftmann@21328
  1452
apply (cases "a = 0", simp)
paulson@14277
  1453
apply (blast intro: inverse_negative_imp_negative negative_imp_inverse_negative)
paulson@14277
  1454
done
paulson@14277
  1455
paulson@14277
  1456
lemma inverse_nonnegative_iff_nonnegative [simp]:
nipkow@23482
  1457
  "(0 \<le> inverse a) = (0 \<le> (a::'a::{ordered_field,division_by_zero}))"
paulson@14277
  1458
by (simp add: linorder_not_less [symmetric])
paulson@14277
  1459
paulson@14277
  1460
lemma inverse_nonpositive_iff_nonpositive [simp]:
nipkow@23482
  1461
  "(inverse a \<le> 0) = (a \<le> (0::'a::{ordered_field,division_by_zero}))"
paulson@14277
  1462
by (simp add: linorder_not_less [symmetric])
paulson@14277
  1463
chaieb@23406
  1464
lemma ordered_field_no_lb: "\<forall> x. \<exists>y. y < (x::'a::ordered_field)"
chaieb@23406
  1465
proof
chaieb@23406
  1466
  fix x::'a
chaieb@23406
  1467
  have m1: "- (1::'a) < 0" by simp
chaieb@23406
  1468
  from add_strict_right_mono[OF m1, where c=x] 
chaieb@23406
  1469
  have "(- 1) + x < x" by simp
chaieb@23406
  1470
  thus "\<exists>y. y < x" by blast
chaieb@23406
  1471
qed
chaieb@23406
  1472
chaieb@23406
  1473
lemma ordered_field_no_ub: "\<forall> x. \<exists>y. y > (x::'a::ordered_field)"
chaieb@23406
  1474
proof
chaieb@23406
  1475
  fix x::'a
chaieb@23406
  1476
  have m1: " (1::'a) > 0" by simp
chaieb@23406
  1477
  from add_strict_right_mono[OF m1, where c=x] 
chaieb@23406
  1478
  have "1 + x > x" by simp
chaieb@23406
  1479
  thus "\<exists>y. y > x" by blast
chaieb@23406
  1480
qed
paulson@14277
  1481
paulson@14277
  1482
subsection{*Anti-Monotonicity of @{term inverse}*}
paulson@14277
  1483
paulson@14268
  1484
lemma less_imp_inverse_less:
nipkow@23482
  1485
assumes less: "a < b" and apos:  "0 < a"
nipkow@23482
  1486
shows "inverse b < inverse (a::'a::ordered_field)"
nipkow@23482
  1487
proof (rule ccontr)
paulson@14268
  1488
  assume "~ inverse b < inverse a"
nipkow@29667
  1489
  hence "inverse a \<le> inverse b" by (simp add: linorder_not_less)
paulson@14268
  1490
  hence "~ (a < b)"
paulson@14268
  1491
    by (simp add: linorder_not_less inverse_le_imp_le [OF _ apos])
nipkow@29667
  1492
  thus False by (rule notE [OF _ less])
nipkow@23482
  1493
qed
paulson@14268
  1494
paulson@14268
  1495
lemma inverse_less_imp_less:
nipkow@23482
  1496
  "[|inverse a < inverse b; 0 < a|] ==> b < (a::'a::ordered_field)"
paulson@14268
  1497
apply (simp add: order_less_le [of "inverse a"] order_less_le [of "b"])
paulson@14268
  1498
apply (force dest!: inverse_le_imp_le nonzero_inverse_eq_imp_eq) 
paulson@14268
  1499
done
paulson@14268
  1500
paulson@14268
  1501
text{*Both premises are essential. Consider -1 and 1.*}
paulson@24286
  1502
lemma inverse_less_iff_less [simp,noatp]:
nipkow@23482
  1503
  "[|0 < a; 0 < b|] ==> (inverse a < inverse b) = (b < (a::'a::ordered_field))"
paulson@14268
  1504
by (blast intro: less_imp_inverse_less dest: inverse_less_imp_less) 
paulson@14268
  1505
paulson@14268
  1506
lemma le_imp_inverse_le:
nipkow@23482
  1507
  "[|a \<le> b; 0 < a|] ==> inverse b \<le> inverse (a::'a::ordered_field)"
nipkow@23482
  1508
by (force simp add: order_le_less less_imp_inverse_less)
paulson@14268
  1509
paulson@24286
  1510
lemma inverse_le_iff_le [simp,noatp]:
nipkow@23482
  1511
 "[|0 < a; 0 < b|] ==> (inverse a \<le> inverse b) = (b \<le> (a::'a::ordered_field))"
paulson@14268
  1512
by (blast intro: le_imp_inverse_le dest: inverse_le_imp_le) 
paulson@14268
  1513
paulson@14268
  1514
paulson@14268
  1515
text{*These results refer to both operands being negative.  The opposite-sign
paulson@14268
  1516
case is trivial, since inverse preserves signs.*}
paulson@14268
  1517
lemma inverse_le_imp_le_neg:
nipkow@23482
  1518
  "[|inverse a \<le> inverse b; b < 0|] ==> b \<le> (a::'a::ordered_field)"
nipkow@23482
  1519
apply (rule classical) 
nipkow@23482
  1520
apply (subgoal_tac "a < 0") 
nipkow@23482
  1521
 prefer 2 apply (force simp add: linorder_not_le intro: order_less_trans) 
nipkow@23482
  1522
apply (insert inverse_le_imp_le [of "-b" "-a"])
nipkow@23482
  1523
apply (simp add: order_less_imp_not_eq nonzero_inverse_minus_eq) 
nipkow@23482
  1524
done
paulson@14268
  1525
paulson@14268
  1526
lemma less_imp_inverse_less_neg:
paulson@14268
  1527
   "[|a < b; b < 0|] ==> inverse b < inverse (a::'a::ordered_field)"
nipkow@23482
  1528
apply (subgoal_tac "a < 0") 
nipkow@23482
  1529
 prefer 2 apply (blast intro: order_less_trans) 
nipkow@23482
  1530
apply (insert less_imp_inverse_less [of "-b" "-a"])
nipkow@23482
  1531
apply (simp add: order_less_imp_not_eq nonzero_inverse_minus_eq) 
nipkow@23482
  1532
done
paulson@14268
  1533
paulson@14268
  1534
lemma inverse_less_imp_less_neg:
paulson@14268
  1535
   "[|inverse a < inverse b; b < 0|] ==> b < (a::'a::ordered_field)"
nipkow@23482
  1536
apply (rule classical) 
nipkow@23482
  1537
apply (subgoal_tac "a < 0") 
nipkow@23482
  1538
 prefer 2
nipkow@23482
  1539
 apply (force simp add: linorder_not_less intro: order_le_less_trans) 
nipkow@23482
  1540
apply (insert inverse_less_imp_less [of "-b" "-a"])
nipkow@23482
  1541
apply (simp add: order_less_imp_not_eq nonzero_inverse_minus_eq) 
nipkow@23482
  1542
done
paulson@14268
  1543
paulson@24286
  1544
lemma inverse_less_iff_less_neg [simp,noatp]:
nipkow@23482
  1545
  "[|a < 0; b < 0|] ==> (inverse a < inverse b) = (b < (a::'a::ordered_field))"
nipkow@23482
  1546
apply (insert inverse_less_iff_less [of "-b" "-a"])
nipkow@23482
  1547
apply (simp del: inverse_less_iff_less 
nipkow@23482
  1548
            add: order_less_imp_not_eq nonzero_inverse_minus_eq)
nipkow@23482
  1549
done
paulson@14268
  1550
paulson@14268
  1551
lemma le_imp_inverse_le_neg:
nipkow@23482
  1552
  "[|a \<le> b; b < 0|] ==> inverse b \<le> inverse (a::'a::ordered_field)"
nipkow@23482
  1553
by (force simp add: order_le_less less_imp_inverse_less_neg)
paulson@14268
  1554
paulson@24286
  1555
lemma inverse_le_iff_le_neg [simp,noatp]:
nipkow@23482
  1556
 "[|a < 0; b < 0|] ==> (inverse a \<le> inverse b) = (b \<le> (a::'a::ordered_field))"
paulson@14268
  1557
by (blast intro: le_imp_inverse_le_neg dest: inverse_le_imp_le_neg) 
paulson@14265
  1558
paulson@14277
  1559
paulson@14365
  1560
subsection{*Inverses and the Number One*}
paulson@14365
  1561
paulson@14365
  1562
lemma one_less_inverse_iff:
nipkow@23482
  1563
  "(1 < inverse x) = (0 < x & x < (1::'a::{ordered_field,division_by_zero}))"
nipkow@23482
  1564
proof cases
paulson@14365
  1565
  assume "0 < x"
paulson@14365
  1566
    with inverse_less_iff_less [OF zero_less_one, of x]
paulson@14365
  1567
    show ?thesis by simp
paulson@14365
  1568
next
paulson@14365
  1569
  assume notless: "~ (0 < x)"
paulson@14365
  1570
  have "~ (1 < inverse x)"
paulson@14365
  1571
  proof
paulson@14365
  1572
    assume "1 < inverse x"
paulson@14365
  1573
    also with notless have "... \<le> 0" by (simp add: linorder_not_less)
paulson@14365
  1574
    also have "... < 1" by (rule zero_less_one) 
paulson@14365
  1575
    finally show False by auto
paulson@14365
  1576
  qed
paulson@14365
  1577
  with notless show ?thesis by simp
paulson@14365
  1578
qed
paulson@14365
  1579
paulson@14365
  1580
lemma inverse_eq_1_iff [simp]:
nipkow@23482
  1581
  "(inverse x = 1) = (x = (1::'a::{field,division_by_zero}))"
paulson@14365
  1582
by (insert inverse_eq_iff_eq [of x 1], simp) 
paulson@14365
  1583
paulson@14365
  1584
lemma one_le_inverse_iff:
nipkow@23482
  1585
  "(1 \<le> inverse x) = (0 < x & x \<le> (1::'a::{ordered_field,division_by_zero}))"
paulson@14365
  1586
by (force simp add: order_le_less one_less_inverse_iff zero_less_one 
paulson@14365
  1587
                    eq_commute [of 1]) 
paulson@14365
  1588
paulson@14365
  1589
lemma inverse_less_1_iff:
nipkow@23482
  1590
  "(inverse x < 1) = (x \<le> 0 | 1 < (x::'a::{ordered_field,division_by_zero}))"
paulson@14365
  1591
by (simp add: linorder_not_le [symmetric] one_le_inverse_iff) 
paulson@14365
  1592
paulson@14365
  1593
lemma inverse_le_1_iff:
nipkow@23482
  1594
  "(inverse x \<le> 1) = (x \<le> 0 | 1 \<le> (x::'a::{ordered_field,division_by_zero}))"
paulson@14365
  1595
by (simp add: linorder_not_less [symmetric] one_less_inverse_iff) 
paulson@14365
  1596
wenzelm@23389
  1597
paulson@14288
  1598
subsection{*Simplification of Inequalities Involving Literal Divisors*}
paulson@14288
  1599
paulson@14288
  1600
lemma pos_le_divide_eq: "0 < (c::'a::ordered_field) ==> (a \<le> b/c) = (a*c \<le> b)"
paulson@14288
  1601
proof -
paulson@14288
  1602
  assume less: "0<c"
paulson@14288
  1603
  hence "(a \<le> b/c) = (a*c \<le> (b/c)*c)"
paulson@14288
  1604
    by (simp add: mult_le_cancel_right order_less_not_sym [OF less])
paulson@14288
  1605
  also have "... = (a*c \<le> b)"
paulson@14288
  1606
    by (simp add: order_less_imp_not_eq2 [OF less] divide_inverse mult_assoc) 
paulson@14288
  1607
  finally show ?thesis .
paulson@14288
  1608
qed
paulson@14288
  1609
paulson@14288
  1610
lemma neg_le_divide_eq: "c < (0::'a::ordered_field) ==> (a \<le> b/c) = (b \<le> a*c)"
paulson@14288
  1611
proof -
paulson@14288
  1612
  assume less: "c<0"
paulson@14288
  1613
  hence "(a \<le> b/c) = ((b/c)*c \<le> a*c)"
paulson@14288
  1614
    by (simp add: mult_le_cancel_right order_less_not_sym [OF less])
paulson@14288
  1615
  also have "... = (b \<le> a*c)"
paulson@14288
  1616
    by (simp add: order_less_imp_not_eq [OF less] divide_inverse mult_assoc) 
paulson@14288
  1617
  finally show ?thesis .
paulson@14288
  1618
qed
paulson@14288
  1619
paulson@14288
  1620
lemma le_divide_eq:
paulson@14288
  1621
  "(a \<le> b/c) = 
paulson@14288
  1622
   (if 0 < c then a*c \<le> b
paulson@14288
  1623
             else if c < 0 then b \<le> a*c
paulson@14288
  1624
             else  a \<le> (0::'a::{ordered_field,division_by_zero}))"
haftmann@21328
  1625
apply (cases "c=0", simp) 
paulson@14288
  1626
apply (force simp add: pos_le_divide_eq neg_le_divide_eq linorder_neq_iff) 
paulson@14288
  1627
done
paulson@14288
  1628
paulson@14288
  1629
lemma pos_divide_le_eq: "0 < (c::'a::ordered_field) ==> (b/c \<le> a) = (b \<le> a*c)"
paulson@14288
  1630
proof -
paulson@14288
  1631
  assume less: "0<c"
paulson@14288
  1632
  hence "(b/c \<le> a) = ((b/c)*c \<le> a*c)"
paulson@14288
  1633
    by (simp add: mult_le_cancel_right order_less_not_sym [OF less])
paulson@14288
  1634
  also have "... = (b \<le> a*c)"
paulson@14288
  1635
    by (simp add: order_less_imp_not_eq2 [OF less] divide_inverse mult_assoc) 
paulson@14288
  1636
  finally show ?thesis .
paulson@14288
  1637
qed
paulson@14288
  1638
paulson@14288
  1639
lemma neg_divide_le_eq: "c < (0::'a::ordered_field) ==> (b/c \<le> a) = (a*c \<le> b)"
paulson@14288
  1640
proof -
paulson@14288
  1641
  assume less: "c<0"
paulson@14288
  1642
  hence "(b/c \<le> a) = (a*c \<le> (b/c)*c)"
paulson@14288
  1643
    by (simp add: mult_le_cancel_right order_less_not_sym [OF less])
paulson@14288
  1644
  also have "... = (a*c \<le> b)"
paulson@14288
  1645
    by (simp add: order_less_imp_not_eq [OF less] divide_inverse mult_assoc) 
paulson@14288
  1646
  finally show ?thesis .
paulson@14288
  1647
qed
paulson@14288
  1648
paulson@14288
  1649
lemma divide_le_eq:
paulson@14288
  1650
  "(b/c \<le> a) = 
paulson@14288
  1651
   (if 0 < c then b \<le> a*c
paulson@14288
  1652
             else if c < 0 then a*c \<le> b
paulson@14288
  1653
             else 0 \<le> (a::'a::{ordered_field,division_by_zero}))"
haftmann@21328
  1654
apply (cases "c=0", simp) 
paulson@14288
  1655
apply (force simp add: pos_divide_le_eq neg_divide_le_eq linorder_neq_iff) 
paulson@14288
  1656
done
paulson@14288
  1657
paulson@14288
  1658
lemma pos_less_divide_eq:
paulson@14288
  1659
     "0 < (c::'a::ordered_field) ==> (a < b/c) = (a*c < b)"
paulson@14288
  1660
proof -
paulson@14288
  1661
  assume less: "0<c"
paulson@14288
  1662
  hence "(a < b/c) = (a*c < (b/c)*c)"
paulson@15234
  1663
    by (simp add: mult_less_cancel_right_disj order_less_not_sym [OF less])
paulson@14288
  1664
  also have "... = (a*c < b)"
paulson@14288
  1665
    by (simp add: order_less_imp_not_eq2 [OF less] divide_inverse mult_assoc) 
paulson@14288
  1666
  finally show ?thesis .
paulson@14288
  1667
qed
paulson@14288
  1668
paulson@14288
  1669
lemma neg_less_divide_eq:
paulson@14288
  1670
 "c < (0::'a::ordered_field) ==> (a < b/c) = (b < a*c)"
paulson@14288
  1671
proof -
paulson@14288
  1672
  assume less: "c<0"
paulson@14288
  1673
  hence "(a < b/c) = ((b/c)*c < a*c)"
paulson@15234
  1674
    by (simp add: mult_less_cancel_right_disj order_less_not_sym [OF less])
paulson@14288
  1675
  also have "... = (b < a*c)"
paulson@14288
  1676
    by (simp add: order_less_imp_not_eq [OF less] divide_inverse mult_assoc) 
paulson@14288
  1677
  finally show ?thesis .
paulson@14288
  1678
qed
paulson@14288
  1679
paulson@14288
  1680
lemma less_divide_eq:
paulson@14288
  1681
  "(a < b/c) = 
paulson@14288
  1682
   (if 0 < c then a*c < b
paulson@14288
  1683
             else if c < 0 then b < a*c
paulson@14288
  1684
             else  a < (0::'a::{ordered_field,division_by_zero}))"
haftmann@21328
  1685
apply (cases "c=0", simp) 
paulson@14288
  1686
apply (force simp add: pos_less_divide_eq neg_less_divide_eq linorder_neq_iff) 
paulson@14288
  1687
done
paulson@14288
  1688
paulson@14288
  1689
lemma pos_divide_less_eq:
paulson@14288
  1690
     "0 < (c::'a::ordered_field) ==> (b/c < a) = (b < a*c)"
paulson@14288
  1691
proof -
paulson@14288
  1692
  assume less: "0<c"
paulson@14288
  1693
  hence "(b/c < a) = ((b/c)*c < a*c)"
paulson@15234
  1694
    by (simp add: mult_less_cancel_right_disj order_less_not_sym [OF less])
paulson@14288
  1695
  also have "... = (b < a*c)"
paulson@14288
  1696
    by (simp add: order_less_imp_not_eq2 [OF less] divide_inverse mult_assoc) 
paulson@14288
  1697
  finally show ?thesis .
paulson@14288
  1698
qed
paulson@14288
  1699
paulson@14288
  1700
lemma neg_divide_less_eq:
paulson@14288
  1701
 "c < (0::'a::ordered_field) ==> (b/c < a) = (a*c < b)"
paulson@14288
  1702
proof -
paulson@14288
  1703
  assume less: "c<0"
paulson@14288
  1704
  hence "(b/c < a) = (a*c < (b/c)*c)"
paulson@15234
  1705
    by (simp add: mult_less_cancel_right_disj order_less_not_sym [OF less])
paulson@14288
  1706
  also have "... = (a*c < b)"
paulson@14288
  1707
    by (simp add: order_less_imp_not_eq [OF less] divide_inverse mult_assoc) 
paulson@14288
  1708
  finally show ?thesis .
paulson@14288
  1709
qed
paulson@14288
  1710
paulson@14288
  1711
lemma divide_less_eq:
paulson@14288
  1712
  "(b/c < a) = 
paulson@14288
  1713
   (if 0 < c then b < a*c
paulson@14288
  1714
             else if c < 0 then a*c < b
paulson@14288
  1715
             else 0 < (a::'a::{ordered_field,division_by_zero}))"
haftmann@21328
  1716
apply (cases "c=0", simp) 
paulson@14288
  1717
apply (force simp add: pos_divide_less_eq neg_divide_less_eq linorder_neq_iff) 
paulson@14288
  1718
done
paulson@14288
  1719
nipkow@23482
  1720
nipkow@23482
  1721
subsection{*Field simplification*}
nipkow@23482
  1722
nipkow@29667
  1723
text{* Lemmas @{text field_simps} multiply with denominators in in(equations)
nipkow@29667
  1724
if they can be proved to be non-zero (for equations) or positive/negative
nipkow@29667
  1725
(for inequations). Can be too aggressive and is therefore separate from the
nipkow@29667
  1726
more benign @{text algebra_simps}. *}
paulson@14288
  1727
nipkow@29833
  1728
lemmas field_simps[noatp] = field_eq_simps
nipkow@23482
  1729
  (* multiply ineqn *)
nipkow@23482
  1730
  pos_divide_less_eq neg_divide_less_eq
nipkow@23482
  1731
  pos_less_divide_eq neg_less_divide_eq
nipkow@23482
  1732
  pos_divide_le_eq neg_divide_le_eq
nipkow@23482
  1733
  pos_le_divide_eq neg_le_divide_eq
paulson@14288
  1734
nipkow@23482
  1735
text{* Lemmas @{text sign_simps} is a first attempt to automate proofs
nipkow@23483
  1736
of positivity/negativity needed for @{text field_simps}. Have not added @{text
nipkow@23482
  1737
sign_simps} to @{text field_simps} because the former can lead to case
nipkow@23482
  1738
explosions. *}
paulson@14288
  1739
nipkow@29833
  1740
lemmas sign_simps[noatp] = group_simps
nipkow@23482
  1741
  zero_less_mult_iff  mult_less_0_iff
paulson@14288
  1742
nipkow@23482
  1743
(* Only works once linear arithmetic is installed:
nipkow@23482
  1744
text{*An example:*}
nipkow@23482
  1745
lemma fixes a b c d e f :: "'a::ordered_field"
nipkow@23482
  1746
shows "\<lbrakk>a>b; c<d; e<f; 0 < u \<rbrakk> \<Longrightarrow>
nipkow@23482
  1747
 ((a-b)*(c-d)*(e-f))/((c-d)*(e-f)*(a-b)) <
nipkow@23482
  1748
 ((e-f)*(a-b)*(c-d))/((e-f)*(a-b)*(c-d)) + u"
nipkow@23482
  1749
apply(subgoal_tac "(c-d)*(e-f)*(a-b) > 0")
nipkow@23482
  1750
 prefer 2 apply(simp add:sign_simps)
nipkow@23482
  1751
apply(subgoal_tac "(c-d)*(e-f)*(a-b)*u > 0")
nipkow@23482
  1752
 prefer 2 apply(simp add:sign_simps)
nipkow@23482
  1753
apply(simp add:field_simps)
avigad@16775
  1754
done
nipkow@23482
  1755
*)
avigad@16775
  1756
wenzelm@23389
  1757
avigad@16775
  1758
subsection{*Division and Signs*}
avigad@16775
  1759
avigad@16775
  1760
lemma zero_less_divide_iff:
avigad@16775
  1761
     "((0::'a::{ordered_field,division_by_zero}) < a/b) = (0 < a & 0 < b | a < 0 & b < 0)"
avigad@16775
  1762
by (simp add: divide_inverse zero_less_mult_iff)
avigad@16775
  1763
avigad@16775
  1764
lemma divide_less_0_iff:
avigad@16775
  1765
     "(a/b < (0::'a::{ordered_field,division_by_zero})) = 
avigad@16775
  1766
      (0 < a & b < 0 | a < 0 & 0 < b)"
avigad@16775
  1767
by (simp add: divide_inverse mult_less_0_iff)
avigad@16775
  1768
avigad@16775
  1769
lemma zero_le_divide_iff:
avigad@16775
  1770
     "((0::'a::{ordered_field,division_by_zero}) \<le> a/b) =
avigad@16775
  1771
      (0 \<le> a & 0 \<le> b | a \<le> 0 & b \<le> 0)"
avigad@16775
  1772
by (simp add: divide_inverse zero_le_mult_iff)
avigad@16775
  1773
avigad@16775
  1774
lemma divide_le_0_iff:
avigad@16775
  1775
     "(a/b \<le> (0::'a::{ordered_field,division_by_zero})) =
avigad@16775
  1776
      (0 \<le> a & b \<le> 0 | a \<le> 0 & 0 \<le> b)"
avigad@16775
  1777
by (simp add: divide_inverse mult_le_0_iff)
avigad@16775
  1778
paulson@24286
  1779
lemma divide_eq_0_iff [simp,noatp]:
avigad@16775
  1780
     "(a/b = 0) = (a=0 | b=(0::'a::{field,division_by_zero}))"
nipkow@23482
  1781
by (simp add: divide_inverse)
avigad@16775
  1782
nipkow@23482
  1783
lemma divide_pos_pos:
nipkow@23482
  1784
  "0 < (x::'a::ordered_field) ==> 0 < y ==> 0 < x / y"
nipkow@23482
  1785
by(simp add:field_simps)
nipkow@23482
  1786
avigad@16775
  1787
nipkow@23482
  1788
lemma divide_nonneg_pos:
nipkow@23482
  1789
  "0 <= (x::'a::ordered_field) ==> 0 < y ==> 0 <= x / y"
nipkow@23482
  1790
by(simp add:field_simps)
avigad@16775
  1791
nipkow@23482
  1792
lemma divide_neg_pos:
nipkow@23482
  1793
  "(x::'a::ordered_field) < 0 ==> 0 < y ==> x / y < 0"
nipkow@23482
  1794
by(simp add:field_simps)
avigad@16775
  1795
nipkow@23482
  1796
lemma divide_nonpos_pos:
nipkow@23482
  1797
  "(x::'a::ordered_field) <= 0 ==> 0 < y ==> x / y <= 0"
nipkow@23482
  1798
by(simp add:field_simps)
avigad@16775
  1799
nipkow@23482
  1800
lemma divide_pos_neg:
nipkow@23482
  1801
  "0 < (x::'a::ordered_field) ==> y < 0 ==> x / y < 0"
nipkow@23482
  1802
by(simp add:field_simps)
avigad@16775
  1803
nipkow@23482
  1804
lemma divide_nonneg_neg:
nipkow@23482
  1805
  "0 <= (x::'a::ordered_field) ==> y < 0 ==> x / y <= 0" 
nipkow@23482
  1806
by(simp add:field_simps)
avigad@16775
  1807
nipkow@23482
  1808
lemma divide_neg_neg:
nipkow@23482
  1809
  "(x::'a::ordered_field) < 0 ==> y < 0 ==> 0 < x / y"
nipkow@23482
  1810
by(simp add:field_simps)
avigad@16775
  1811
nipkow@23482
  1812
lemma divide_nonpos_neg:
nipkow@23482
  1813
  "(x::'a::ordered_field) <= 0 ==> y < 0 ==> 0 <= x / y"
nipkow@23482
  1814
by(simp add:field_simps)
paulson@15234
  1815
wenzelm@23389
  1816
paulson@14288
  1817
subsection{*Cancellation Laws for Division*}
paulson@14288
  1818
paulson@24286
  1819
lemma divide_cancel_right [simp,noatp]:
paulson@14288
  1820
     "(a/c = b/c) = (c = 0 | a = (b::'a::{field,division_by_zero}))"
nipkow@23482
  1821
apply (cases "c=0", simp)
nipkow@23496
  1822
apply (simp add: divide_inverse)
paulson@14288
  1823
done
paulson@14288
  1824
paulson@24286
  1825
lemma divide_cancel_left [simp,noatp]:
paulson@14288
  1826
     "(c/a = c/b) = (c = 0 | a = (b::'a::{field,division_by_zero}))" 
nipkow@23482
  1827
apply (cases "c=0", simp)
nipkow@23496
  1828
apply (simp add: divide_inverse)
paulson@14288
  1829
done
paulson@14288
  1830
wenzelm@23389
  1831
paulson@14353
  1832
subsection {* Division and the Number One *}
paulson@14353
  1833
paulson@14353
  1834
text{*Simplify expressions equated with 1*}
paulson@24286
  1835
lemma divide_eq_1_iff [simp,noatp]:
paulson@14353
  1836
     "(a/b = 1) = (b \<noteq> 0 & a = (b::'a::{field,division_by_zero}))"
nipkow@23482
  1837
apply (cases "b=0", simp)
nipkow@23482
  1838
apply (simp add: right_inverse_eq)
paulson@14353
  1839
done
paulson@14353
  1840
paulson@24286
  1841
lemma one_eq_divide_iff [simp,noatp]:
paulson@14353
  1842
     "(1 = a/b) = (b \<noteq> 0 & a = (b::'a::{field,division_by_zero}))"
nipkow@23482
  1843
by (simp add: eq_commute [of 1])
paulson@14353
  1844
paulson@24286
  1845
lemma zero_eq_1_divide_iff [simp,noatp]:
paulson@14353
  1846
     "((0::'a::{ordered_field,division_by_zero}) = 1/a) = (a = 0)"
nipkow@23482
  1847
apply (cases "a=0", simp)
nipkow@23482
  1848
apply (auto simp add: nonzero_eq_divide_eq)
paulson@14353
  1849
done
paulson@14353
  1850
paulson@24286
  1851
lemma one_divide_eq_0_iff [simp,noatp]:
paulson@14353
  1852
     "(1/a = (0::'a::{ordered_field,division_by_zero})) = (a = 0)"
nipkow@23482
  1853
apply (cases "a=0", simp)
nipkow@23482
  1854
apply (insert zero_neq_one [THEN not_sym])
nipkow@23482
  1855
apply (auto simp add: nonzero_divide_eq_eq)
paulson@14353
  1856
done
paulson@14353
  1857
paulson@14353
  1858
text{*Simplify expressions such as @{text "0 < 1/x"} to @{text "0 < x"}*}
paulson@18623
  1859
lemmas zero_less_divide_1_iff = zero_less_divide_iff [of 1, simplified]
paulson@18623
  1860
lemmas divide_less_0_1_iff = divide_less_0_iff [of 1, simplified]
paulson@18623
  1861
lemmas zero_le_divide_1_iff = zero_le_divide_iff [of 1, simplified]
paulson@18623
  1862
lemmas divide_le_0_1_iff = divide_le_0_iff [of 1, simplified]
paulson@17085
  1863
nipkow@29833
  1864
declare zero_less_divide_1_iff [simp,noatp]
paulson@24286
  1865
declare divide_less_0_1_iff [simp,noatp]
nipkow@29833
  1866
declare zero_le_divide_1_iff [simp,noatp]
paulson@24286
  1867
declare divide_le_0_1_iff [simp,noatp]
paulson@14353
  1868
wenzelm@23389
  1869
paulson@14293
  1870
subsection {* Ordering Rules for Division *}
paulson@14293
  1871
paulson@14293
  1872
lemma divide_strict_right_mono:
paulson@14293
  1873
     "[|a < b; 0 < c|] ==> a / c < b / (c::'a::ordered_field)"
paulson@14293
  1874
by (simp add: order_less_imp_not_eq2 divide_inverse mult_strict_right_mono 
nipkow@23482
  1875
              positive_imp_inverse_positive)
paulson@14293
  1876
paulson@14293
  1877
lemma divide_right_mono:
paulson@14293
  1878
     "[|a \<le> b; 0 \<le> c|] ==> a/c \<le> b/(c::'a::{ordered_field,division_by_zero})"
nipkow@23482
  1879
by (force simp add: divide_strict_right_mono order_le_less)
paulson@14293
  1880
avigad@16775
  1881
lemma divide_right_mono_neg: "(a::'a::{division_by_zero,ordered_field}) <= b 
avigad@16775
  1882
    ==> c <= 0 ==> b / c <= a / c"
nipkow@23482
  1883
apply (drule divide_right_mono [of _ _ "- c"])
nipkow@23482
  1884
apply auto
avigad@16775
  1885
done
avigad@16775
  1886
avigad@16775
  1887
lemma divide_strict_right_mono_neg:
avigad@16775
  1888
     "[|b < a; c < 0|] ==> a / c < b / (c::'a::ordered_field)"
nipkow@23482
  1889
apply (drule divide_strict_right_mono [of _ _ "-c"], simp)
nipkow@23482
  1890
apply (simp add: order_less_imp_not_eq nonzero_minus_divide_right [symmetric])
avigad@16775
  1891
done
paulson@14293
  1892
paulson@14293
  1893
text{*The last premise ensures that @{term a} and @{term b} 
paulson@14293
  1894
      have the same sign*}
paulson@14293
  1895
lemma divide_strict_left_mono:
nipkow@23482
  1896
  "[|b < a; 0 < c; 0 < a*b|] ==> c / a < c / (b::'a::ordered_field)"
nipkow@23482
  1897
by(auto simp: field_simps times_divide_eq zero_less_mult_iff mult_strict_right_mono)
paulson@14293
  1898
paulson@14293
  1899
lemma divide_left_mono:
nipkow@23482
  1900
  "[|b \<le> a; 0 \<le> c; 0 < a*b|] ==> c / a \<le> c / (b::'a::ordered_field)"
nipkow@23482
  1901
by(auto simp: field_simps times_divide_eq zero_less_mult_iff mult_right_mono)
paulson@14293
  1902
avigad@16775
  1903
lemma divide_left_mono_neg: "(a::'a::{division_by_zero,ordered_field}) <= b 
avigad@16775
  1904
    ==> c <= 0 ==> 0 < a * b ==> c / a <= c / b"
avigad@16775
  1905
  apply (drule divide_left_mono [of _ _ "- c"])
avigad@16775
  1906
  apply (auto simp add: mult_commute)
avigad@16775
  1907
done
avigad@16775
  1908
paulson@14293
  1909
lemma divide_strict_left_mono_neg:
nipkow@23482
  1910
  "[|a < b; c < 0; 0 < a*b|] ==> c / a < c / (b::'a::ordered_field)"
nipkow@23482
  1911
by(auto simp: field_simps times_divide_eq zero_less_mult_iff mult_strict_right_mono_neg)
nipkow@23482
  1912
paulson@14293
  1913
avigad@16775
  1914
text{*Simplify quotients that are compared with the value 1.*}
avigad@16775
  1915
paulson@24286
  1916
lemma le_divide_eq_1 [noatp]:
avigad@16775
  1917
  fixes a :: "'a :: {ordered_field,division_by_zero}"
avigad@16775
  1918
  shows "(1 \<le> b / a) = ((0 < a & a \<le> b) | (a < 0 & b \<le> a))"
avigad@16775
  1919
by (auto simp add: le_divide_eq)
avigad@16775
  1920
paulson@24286
  1921
lemma divide_le_eq_1 [noatp]:
avigad@16775
  1922
  fixes a :: "'a :: {ordered_field,division_by_zero}"
avigad@16775
  1923
  shows "(b / a \<le> 1) = ((0 < a & b \<le> a) | (a < 0 & a \<le> b) | a=0)"
avigad@16775
  1924
by (auto simp add: divide_le_eq)
avigad@16775
  1925
paulson@24286
  1926
lemma less_divide_eq_1 [noatp]:
avigad@16775
  1927
  fixes a :: "'a :: {ordered_field,division_by_zero}"
avigad@16775
  1928
  shows "(1 < b / a) = ((0 < a & a < b) | (a < 0 & b < a))"
avigad@16775
  1929
by (auto simp add: less_divide_eq)
avigad@16775
  1930
paulson@24286
  1931
lemma divide_less_eq_1 [noatp]:
avigad@16775
  1932
  fixes a :: "'a :: {ordered_field,division_by_zero}"
avigad@16775
  1933
  shows "(b / a < 1) = ((0 < a & b < a) | (a < 0 & a < b) | a=0)"
avigad@16775
  1934
by (auto simp add: divide_less_eq)
avigad@16775
  1935
wenzelm@23389
  1936
avigad@16775
  1937
subsection{*Conditional Simplification Rules: No Case Splits*}
avigad@16775
  1938
paulson@24286
  1939
lemma le_divide_eq_1_pos [simp,noatp]:
avigad@16775
  1940
  fixes a :: "'a :: {ordered_field,division_by_zero}"
paulson@18649
  1941
  shows "0 < a \<Longrightarrow> (1 \<le> b/a) = (a \<le> b)"
avigad@16775
  1942
by (auto simp add: le_divide_eq)
avigad@16775
  1943
paulson@24286
  1944
lemma le_divide_eq_1_neg [simp,noatp]:
avigad@16775
  1945
  fixes a :: "'a :: {ordered_field,division_by_zero}"
paulson@18649
  1946
  shows "a < 0 \<Longrightarrow> (1 \<le> b/a) = (b \<le> a)"
avigad@16775
  1947
by (auto simp add: le_divide_eq)
avigad@16775
  1948
paulson@24286
  1949
lemma divide_le_eq_1_pos [simp,noatp]:
avigad@16775
  1950
  fixes a :: "'a :: {ordered_field,division_by_zero}"
paulson@18649
  1951
  shows "0 < a \<Longrightarrow> (b/a \<le> 1) = (b \<le> a)"
avigad@16775
  1952
by (auto simp add: divide_le_eq)
avigad@16775
  1953
paulson@24286
  1954
lemma divide_le_eq_1_neg [simp,noatp]:
avigad@16775
  1955
  fixes a :: "'a :: {ordered_field,division_by_zero}"
paulson@18649
  1956
  shows "a < 0 \<Longrightarrow> (b/a \<le> 1) = (a \<le> b)"
avigad@16775
  1957
by (auto simp add: divide_le_eq)
avigad@16775
  1958
paulson@24286
  1959
lemma less_divide_eq_1_pos [simp,noatp]:
avigad@16775
  1960
  fixes a :: "'a :: {ordered_field,division_by_zero}"
paulson@18649
  1961
  shows "0 < a \<Longrightarrow> (1 < b/a) = (a < b)"
avigad@16775
  1962
by (auto simp add: less_divide_eq)
avigad@16775
  1963
paulson@24286
  1964
lemma less_divide_eq_1_neg [simp,noatp]:
avigad@16775
  1965
  fixes a :: "'a :: {ordered_field,division_by_zero}"
paulson@18649
  1966
  shows "a < 0 \<Longrightarrow> (1 < b/a) = (b < a)"
avigad@16775
  1967
by (auto simp add: less_divide_eq)
avigad@16775
  1968
paulson@24286
  1969
lemma divide_less_eq_1_pos [simp,noatp]:
avigad@16775
  1970
  fixes a :: "'a :: {ordered_field,division_by_zero}"
paulson@18649
  1971
  shows "0 < a \<Longrightarrow> (b/a < 1) = (b < a)"
paulson@18649
  1972
by (auto simp add: divide_less_eq)
paulson@18649
  1973
paulson@24286
  1974
lemma divide_less_eq_1_neg [simp,noatp]:
paulson@18649
  1975
  fixes a :: "'a :: {ordered_field,division_by_zero}"
paulson@18649
  1976
  shows "a < 0 \<Longrightarrow> b/a < 1 <-> a < b"
avigad@16775
  1977
by (auto simp add: divide_less_eq)
avigad@16775
  1978
paulson@24286
  1979
lemma eq_divide_eq_1 [simp,noatp]:
avigad@16775
  1980
  fixes a :: "'a :: {ordered_field,division_by_zero}"
paulson@18649
  1981
  shows "(1 = b/a) = ((a \<noteq> 0 & a = b))"
avigad@16775
  1982
by (auto simp add: eq_divide_eq)
avigad@16775
  1983
paulson@24286
  1984
lemma divide_eq_eq_1 [simp,noatp]:
avigad@16775
  1985
  fixes a :: "'a :: {ordered_field,division_by_zero}"
paulson@18649
  1986
  shows "(b/a = 1) = ((a \<noteq> 0 & a = b))"
avigad@16775
  1987
by (auto simp add: divide_eq_eq)
avigad@16775
  1988
wenzelm@23389
  1989
avigad@16775
  1990
subsection {* Reasoning about inequalities with division *}
avigad@16775
  1991
avigad@16775
  1992
lemma mult_right_le_one_le: "0 <= (x::'a::ordered_idom) ==> 0 <= y ==> y <= 1
avigad@16775
  1993
    ==> x * y <= x"
nipkow@29667
  1994
by (auto simp add: mult_compare_simps);
avigad@16775
  1995
avigad@16775
  1996
lemma mult_left_le_one_le: "0 <= (x::'a::ordered_idom) ==> 0 <= y ==> y <= 1
avigad@16775
  1997
    ==> y * x <= x"
nipkow@29667
  1998
by (auto simp add: mult_compare_simps);
avigad@16775
  1999
avigad@16775
  2000
lemma mult_imp_div_pos_le: "0 < (y::'a::ordered_field) ==> x <= z * y ==>
avigad@16775
  2001
    x / y <= z";
nipkow@29667
  2002
by (subst pos_divide_le_eq, assumption+);
avigad@16775
  2003
avigad@16775
  2004
lemma mult_imp_le_div_pos: "0 < (y::'a::ordered_field) ==> z * y <= x ==>
nipkow@23482
  2005
    z <= x / y"
nipkow@23482
  2006
by(simp add:field_simps)
avigad@16775
  2007
avigad@16775
  2008
lemma mult_imp_div_pos_less: "0 < (y::'a::ordered_field) ==> x < z * y ==>
avigad@16775
  2009
    x / y < z"
nipkow@23482
  2010
by(simp add:field_simps)
avigad@16775
  2011
avigad@16775
  2012
lemma mult_imp_less_div_pos: "0 < (y::'a::ordered_field) ==> z * y < x ==>
avigad@16775
  2013
    z < x / y"
nipkow@23482
  2014
by(simp add:field_simps)
avigad@16775
  2015
avigad@16775
  2016
lemma frac_le: "(0::'a::ordered_field) <= x ==> 
avigad@16775
  2017
    x <= y ==> 0 < w ==> w <= z  ==> x / z <= y / w"
avigad@16775
  2018
  apply (rule mult_imp_div_pos_le)
haftmann@25230
  2019
  apply simp
haftmann@25230
  2020
  apply (subst times_divide_eq_left)
avigad@16775
  2021
  apply (rule mult_imp_le_div_pos, assumption)
avigad@16775
  2022
  apply (rule mult_mono)
avigad@16775
  2023
  apply simp_all
paulson@14293
  2024
done
paulson@14293
  2025
avigad@16775
  2026
lemma frac_less: "(0::'a::ordered_field) <= x ==> 
avigad@16775
  2027
    x < y ==> 0 < w ==> w <= z  ==> x / z < y / w"
avigad@16775
  2028
  apply (rule mult_imp_div_pos_less)
avigad@16775
  2029
  apply simp;
avigad@16775
  2030
  apply (subst times_divide_eq_left);
avigad@16775
  2031
  apply (rule mult_imp_less_div_pos, assumption)
avigad@16775
  2032
  apply (erule mult_less_le_imp_less)
avigad@16775
  2033
  apply simp_all
avigad@16775
  2034
done
avigad@16775
  2035
avigad@16775
  2036
lemma frac_less2: "(0::'a::ordered_field) < x ==> 
avigad@16775
  2037
    x <= y ==> 0 < w ==> w < z  ==> x / z < y / w"
avigad@16775
  2038
  apply (rule mult_imp_div_pos_less)
avigad@16775
  2039
  apply simp_all
avigad@16775
  2040
  apply (subst times_divide_eq_left);
avigad@16775
  2041
  apply (rule mult_imp_less_div_pos, assumption)
avigad@16775
  2042
  apply (erule mult_le_less_imp_less)
avigad@16775
  2043
  apply simp_all
avigad@16775
  2044
done
avigad@16775
  2045
avigad@16775
  2046
text{*It's not obvious whether these should be simprules or not. 
avigad@16775
  2047
  Their effect is to gather terms into one big fraction, like
avigad@16775
  2048
  a*b*c / x*y*z. The rationale for that is unclear, but many proofs 
avigad@16775
  2049
  seem to need them.*}
avigad@16775
  2050
avigad@16775
  2051
declare times_divide_eq [simp]
paulson@14293
  2052
wenzelm@23389
  2053
paulson@14293
  2054
subsection {* Ordered Fields are Dense *}
paulson@14293
  2055
haftmann@25193
  2056
context ordered_semidom
haftmann@25193
  2057
begin
haftmann@25193
  2058
haftmann@25193
  2059
lemma less_add_one: "a < a + 1"
paulson@14293
  2060
proof -
haftmann@25193
  2061
  have "a + 0 < a + 1"
nipkow@23482
  2062
    by (blast intro: zero_less_one add_strict_left_mono)
paulson@14293
  2063
  thus ?thesis by simp
paulson@14293
  2064
qed
paulson@14293
  2065
haftmann@25193
  2066
lemma zero_less_two: "0 < 1 + 1"
nipkow@29667
  2067
by (blast intro: less_trans zero_less_one less_add_one)
haftmann@25193
  2068
haftmann@25193
  2069
end
paulson@14365
  2070
paulson@14293
  2071
lemma less_half_sum: "a < b ==> a < (a+b) / (1+1::'a::ordered_field)"
nipkow@23482
  2072
by (simp add: field_simps zero_less_two)
paulson@14293
  2073
paulson@14293
  2074
lemma gt_half_sum: "a < b ==> (a+b)/(1+1::'a::ordered_field) < b"
nipkow@23482
  2075
by (simp add: field_simps zero_less_two)
paulson@14293
  2076
haftmann@24422
  2077
instance ordered_field < dense_linear_order
haftmann@24422
  2078
proof
haftmann@24422
  2079
  fix x y :: 'a
haftmann@24422
  2080
  have "x < x + 1" by simp
haftmann@24422
  2081
  then show "\<exists>y. x < y" .. 
haftmann@24422
  2082
  have "x - 1 < x" by simp
haftmann@24422
  2083
  then show "\<exists>y. y < x" ..
haftmann@24422
  2084
  show "x < y \<Longrightarrow> \<exists>z>x. z < y" by (blast intro!: less_half_sum gt_half_sum)
haftmann@24422
  2085
qed
paulson@14293
  2086
paulson@15234
  2087
paulson@14293
  2088
subsection {* Absolute Value *}
paulson@14293
  2089
haftmann@25304
  2090
context ordered_idom
haftmann@25304
  2091
begin
haftmann@25304
  2092
haftmann@25304
  2093
lemma mult_sgn_abs: "sgn x * abs x = x"
haftmann@25304
  2094
  unfolding abs_if sgn_if by auto
haftmann@25304
  2095
haftmann@25304
  2096
end
nipkow@24491
  2097
obua@14738
  2098
lemma abs_one [simp]: "abs 1 = (1::'a::ordered_idom)"
nipkow@29667
  2099
by (simp add: abs_if zero_less_one [THEN order_less_not_sym])
haftmann@25304
  2100
haftmann@25304
  2101
class pordered_ring_abs = pordered_ring + pordered_ab_group_add_abs +
haftmann@25304
  2102
  assumes abs_eq_mult:
haftmann@25304
  2103
    "(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
  2104
haftmann@25304
  2105
haftmann@25304
  2106
class lordered_ring = pordered_ring + lordered_ab_group_add_abs
haftmann@25304
  2107
begin
haftmann@25304
  2108
huffman@27516
  2109
subclass lordered_ab_group_add_meet ..
huffman@27516
  2110
subclass lordered_ab_group_add_join ..
haftmann@25304
  2111
haftmann@25304
  2112
end
paulson@14294
  2113
obua@14738
  2114
lemma abs_le_mult: "abs (a * b) \<le> (abs a) * (abs (b::'a::lordered_ring))" 
obua@14738
  2115
proof -
obua@14738
  2116
  let ?x = "pprt a * pprt b - pprt a * nprt b - nprt a * pprt b + nprt a * nprt b"
obua@14738
  2117
  let ?y = "pprt a * pprt b + pprt a * nprt b + nprt a * pprt b + nprt a * nprt b"
obua@14738
  2118
  have a: "(abs a) * (abs b) = ?x"
nipkow@29667
  2119
    by (simp only: abs_prts[of a] abs_prts[of b] algebra_simps)
obua@14738
  2120
  {
obua@14738
  2121
    fix u v :: 'a
paulson@15481
  2122
    have bh: "\<lbrakk>u = a; v = b\<rbrakk> \<Longrightarrow> 
paulson@15481
  2123
              u * v = pprt a * pprt b + pprt a * nprt b + 
paulson@15481
  2124
                      nprt a * pprt b + nprt a * nprt b"
obua@14738
  2125
      apply (subst prts[of u], subst prts[of v])
nipkow@29667
  2126
      apply (simp add: algebra_simps) 
obua@14738
  2127
      done
obua@14738
  2128
  }
obua@14738
  2129
  note b = this[OF refl[of a] refl[of b]]
obua@14738
  2130
  note addm = add_mono[of "0::'a" _ "0::'a", simplified]
obua@14738
  2131
  note addm2 = add_mono[of _ "0::'a" _ "0::'a", simplified]
obua@14738
  2132
  have xy: "- ?x <= ?y"
obua@14754
  2133
    apply (simp)
obua@14754
  2134
    apply (rule_tac y="0::'a" in order_trans)
nipkow@16568
  2135
    apply (rule addm2)
avigad@16775
  2136
    apply (simp_all add: mult_nonneg_nonneg mult_nonpos_nonpos)
nipkow@16568
  2137
    apply (rule addm)
avigad@16775
  2138
    apply (simp_all add: mult_nonneg_nonneg mult_nonpos_nonpos)
obua@14754
  2139
    done
obua@14738
  2140
  have yx: "?y <= ?x"
nipkow@16568
  2141
    apply (simp add:diff_def)
obua@14754
  2142
    apply (rule_tac y=0 in order_trans)
avigad@16775
  2143
    apply (rule addm2, (simp add: mult_nonneg_nonpos mult_nonneg_nonpos2)+)
avigad@16775
  2144
    apply (rule addm, (simp add: mult_nonneg_nonpos mult_nonneg_nonpos2)+)
obua@14738
  2145
    done
obua@14738
  2146
  have i1: "a*b <= abs a * abs b" by (simp only: a b yx)
obua@14738
  2147
  have i2: "- (abs a * abs b) <= a*b" by (simp only: a b xy)
obua@14738
  2148
  show ?thesis
obua@14738
  2149
    apply (rule abs_leI)
obua@14738
  2150
    apply (simp add: i1)
obua@14738
  2151
    apply (simp add: i2[simplified minus_le_iff])
obua@14738
  2152
    done
obua@14738
  2153
qed
paulson@14294
  2154
haftmann@25304
  2155
instance lordered_ring \<subseteq> pordered_ring_abs
haftmann@25304
  2156
proof
haftmann@25304
  2157
  fix a b :: "'a\<Colon> lordered_ring"
haftmann@25304
  2158
  assume "(0 \<le> a \<or> a \<le> 0) \<and> (0 \<le> b \<or> b \<le> 0)"
haftmann@25304
  2159
  show "abs (a*b) = abs a * abs b"
obua@14738
  2160
proof -
obua@14738
  2161
  have s: "(0 <= a*b) | (a*b <= 0)"
obua@14738
  2162
    apply (auto)    
obua@14738
  2163
    apply (rule_tac split_mult_pos_le)
obua@14738
  2164
    apply (rule_tac contrapos_np[of "a*b <= 0"])
obua@14738
  2165
    apply (simp)
obua@14738
  2166
    apply (rule_tac split_mult_neg_le)
obua@14738
  2167
    apply (insert prems)
obua@14738
  2168
    apply (blast)
obua@14738
  2169
    done
obua@14738
  2170
  have mulprts: "a * b = (pprt a + nprt a) * (pprt b + nprt b)"
obua@14738
  2171
    by (simp add: prts[symmetric])
obua@14738
  2172
  show ?thesis
obua@14738
  2173
  proof cases
obua@14738
  2174
    assume "0 <= a * b"
obua@14738
  2175
    then show ?thesis
obua@14738
  2176
      apply (simp_all add: mulprts abs_prts)
obua@14738
  2177
      apply (insert prems)
obua@14754
  2178
      apply (auto simp add: 
nipkow@29667
  2179
	algebra_simps 
haftmann@25078
  2180
	iffD1[OF zero_le_iff_zero_nprt] iffD1[OF le_zero_iff_zero_pprt]
haftmann@25078
  2181
	iffD1[OF le_zero_iff_pprt_id] iffD1[OF zero_le_iff_nprt_id])
avigad@16775
  2182
	apply(drule (1) mult_nonneg_nonpos[of a b], simp)
avigad@16775
  2183
	apply(drule (1) mult_nonneg_nonpos2[of b a], simp)
obua@14738
  2184
      done
obua@14738
  2185
  next
obua@14738
  2186
    assume "~(0 <= a*b)"
obua@14738
  2187
    with s have "a*b <= 0" by simp
obua@14738
  2188
    then show ?thesis
obua@14738
  2189
      apply (simp_all add: mulprts abs_prts)
obua@14738
  2190
      apply (insert prems)
nipkow@29667
  2191
      apply (auto simp add: algebra_simps)
avigad@16775
  2192
      apply(drule (1) mult_nonneg_nonneg[of a b],simp)
avigad@16775
  2193
      apply(drule (1) mult_nonpos_nonpos[of a b],simp)
obua@14738
  2194
      done
obua@14738
  2195
  qed
obua@14738
  2196
qed
haftmann@25304
  2197
qed
haftmann@25304
  2198
haftmann@25304
  2199
instance ordered_idom \<subseteq> pordered_ring_abs
haftmann@25304
  2200
by default (auto simp add: abs_if not_less
haftmann@25304
  2201
  equal_neg_zero neg_equal_zero mult_less_0_iff)
paulson@14294
  2202
obua@14738
  2203
lemma abs_mult: "abs (a * b) = abs a * abs (b::'a::ordered_idom)" 
nipkow@29667
  2204
by (simp add: abs_eq_mult linorder_linear)
paulson@14293
  2205
obua@14738
  2206
lemma abs_mult_self: "abs a * abs a = a * (a::'a::ordered_idom)"
nipkow@29667
  2207
by (simp add: abs_if) 
paulson@14294
  2208
paulson@14294
  2209
lemma nonzero_abs_inverse:
paulson@14294
  2210
     "a \<noteq> 0 ==> abs (inverse (a::'a::ordered_field)) = inverse (abs a)"
paulson@14294
  2211
apply (auto simp add: linorder_neq_iff abs_if nonzero_inverse_minus_eq 
paulson@14294
  2212
                      negative_imp_inverse_negative)
paulson@14294
  2213
apply (blast intro: positive_imp_inverse_positive elim: order_less_asym) 
paulson@14294
  2214
done
paulson@14294
  2215
paulson@14294
  2216
lemma abs_inverse [simp]:
paulson@14294
  2217
     "abs (inverse (a::'a::{ordered_field,division_by_zero})) = 
paulson@14294
  2218
      inverse (abs a)"
haftmann@21328
  2219
apply (cases "a=0", simp) 
paulson@14294
  2220
apply (simp add: nonzero_abs_inverse) 
paulson@14294
  2221
done
paulson@14294
  2222
paulson@14294
  2223
lemma nonzero_abs_divide:
paulson@14294
  2224
     "b \<noteq> 0 ==> abs (a / (b::'a::ordered_field)) = abs a / abs b"
paulson@14294
  2225
by (simp add: divide_inverse abs_mult nonzero_abs_inverse) 
paulson@14294
  2226
paulson@15234
  2227
lemma abs_divide [simp]:
paulson@14294
  2228
     "abs (a / (b::'a::{ordered_field,division_by_zero})) = abs a / abs b"
haftmann@21328
  2229
apply (cases "b=0", simp) 
paulson@14294
  2230
apply (simp add: nonzero_abs_divide) 
paulson@14294
  2231
done
paulson@14294
  2232
paulson@14294
  2233
lemma abs_mult_less:
obua@14738
  2234
     "[| abs a < c; abs b < d |] ==> abs a * abs b < c*(d::'a::ordered_idom)"
paulson@14294
  2235
proof -
paulson@14294
  2236
  assume ac: "abs a < c"
paulson@14294
  2237
  hence cpos: "0<c" by (blast intro: order_le_less_trans abs_ge_zero)
paulson@14294
  2238
  assume "abs b < d"
paulson@14294
  2239
  thus ?thesis by (simp add: ac cpos mult_strict_mono) 
paulson@14294
  2240
qed
paulson@14293
  2241
nipkow@29833
  2242
lemmas eq_minus_self_iff[noatp] = equal_neg_zero
obua@14738
  2243
obua@14738
  2244
lemma less_minus_self_iff: "(a < -a) = (a < (0::'a::ordered_idom))"
haftmann@25304
  2245
  unfolding order_less_le less_eq_neg_nonpos equal_neg_zero ..
obua@14738
  2246
obua@14738
  2247
lemma abs_less_iff: "(abs a < b) = (a < b & -a < (b::'a::ordered_idom))" 
obua@14738
  2248
apply (simp add: order_less_le abs_le_iff)  
haftmann@25304
  2249
apply (auto simp add: abs_if neg_less_eq_nonneg less_eq_neg_nonpos)
obua@14738
  2250
done
obua@14738
  2251
avigad@16775
  2252
lemma abs_mult_pos: "(0::'a::ordered_idom) <= x ==> 
haftmann@25304
  2253
    (abs y) * x = abs (y * x)"
haftmann@25304
  2254
  apply (subst abs_mult)
haftmann@25304
  2255
  apply simp
haftmann@25304
  2256
done
avigad@16775
  2257
avigad@16775
  2258
lemma abs_div_pos: "(0::'a::{division_by_zero,ordered_field}) < y ==> 
haftmann@25304
  2259
    abs x / y = abs (x / y)"
haftmann@25304
  2260
  apply (subst abs_divide)
haftmann@25304
  2261
  apply (simp add: order_less_imp_le)
haftmann@25304
  2262
done
avigad@16775
  2263
wenzelm@23389
  2264
obua@19404
  2265
subsection {* Bounds of products via negative and positive Part *}
obua@15178
  2266
obua@15580
  2267
lemma mult_le_prts:
obua@15580
  2268
  assumes
obua@15580
  2269
  "a1 <= (a::'a::lordered_ring)"
obua@15580
  2270
  "a <= a2"
obua@15580
  2271
  "b1 <= b"
obua@15580
  2272
  "b <= b2"
obua@15580
  2273
  shows
obua@15580
  2274
  "a * b <= pprt a2 * pprt b2 + pprt a1 * nprt b2 + nprt a2 * pprt b1 + nprt a1 * nprt b1"
obua@15580
  2275
proof - 
obua@15580
  2276
  have "a * b = (pprt a + nprt a) * (pprt b + nprt b)" 
obua@15580
  2277
    apply (subst prts[symmetric])+
obua@15580
  2278
    apply simp
obua@15580
  2279
    done
obua@15580
  2280
  then have "a * b = pprt a * pprt b + pprt a * nprt b + nprt a * pprt b + nprt a * nprt b"
nipkow@29667
  2281
    by (simp add: algebra_simps)
obua@15580
  2282
  moreover have "pprt a * pprt b <= pprt a2 * pprt b2"
obua@15580
  2283
    by (simp_all add: prems mult_mono)
obua@15580
  2284
  moreover have "pprt a * nprt b <= pprt a1 * nprt b2"
obua@15580
  2285
  proof -
obua@15580
  2286
    have "pprt a * nprt b <= pprt a * nprt b2"
obua@15580
  2287
      by (simp add: mult_left_mono prems)
obua@15580
  2288
    moreover have "pprt a * nprt b2 <= pprt a1 * nprt b2"
obua@15580
  2289
      by (simp add: mult_right_mono_neg prems)
obua@15580
  2290
    ultimately show ?thesis
obua@15580
  2291
      by simp
obua@15580
  2292
  qed
obua@15580
  2293
  moreover have "nprt a * pprt b <= nprt a2 * pprt b1"
obua@15580
  2294
  proof - 
obua@15580
  2295
    have "nprt a * pprt b <= nprt a2 * pprt b"
obua@15580
  2296
      by (simp add: mult_right_mono prems)
obua@15580
  2297
    moreover have "nprt a2 * pprt b <= nprt a2 * pprt b1"
obua@15580
  2298
      by (simp add: mult_left_mono_neg prems)
obua@15580
  2299
    ultimately show ?thesis
obua@15580
  2300
      by simp
obua@15580
  2301
  qed
obua@15580
  2302
  moreover have "nprt a * nprt b <= nprt a1 * nprt b1"
obua@15580
  2303
  proof -
obua@15580
  2304
    have "nprt a * nprt b <= nprt a * nprt b1"
obua@15580
  2305
      by (simp add: mult_left_mono_neg prems)
obua@15580
  2306
    moreover have "nprt a * nprt b1 <= nprt a1 * nprt b1"
obua@15580
  2307
      by (simp add: mult_right_mono_neg prems)
obua@15580
  2308
    ultimately show ?thesis
obua@15580
  2309
      by simp
obua@15580
  2310
  qed
obua@15580
  2311
  ultimately show ?thesis
obua@15580
  2312
    by - (rule add_mono | simp)+
obua@15580
  2313
qed
obua@19404
  2314
obua@19404
  2315
lemma mult_ge_prts:
obua@15178
  2316
  assumes
obua@19404
  2317
  "a1 <= (a::'a::lordered_ring)"
obua@19404
  2318
  "a <= a2"
obua@19404
  2319
  "b1 <= b"
obua@19404
  2320
  "b <= b2"
obua@15178
  2321
  shows
obua@19404
  2322
  "a * b >= nprt a1 * pprt b2 + nprt a2 * nprt b2 + pprt a1 * pprt b1 + pprt a2 * nprt b1"
obua@19404
  2323
proof - 
obua@19404
  2324
  from prems have a1:"- a2 <= -a" by auto
obua@19404
  2325
  from prems have a2: "-a <= -a1" by auto
obua@19404
  2326
  from mult_le_prts[of "-a2" "-a" "-a1" "b1" b "b2", OF a1 a2 prems(3) prems(4), simplified nprt_neg pprt_neg] 
obua@19404
  2327
  have le: "- (a * b) <= - nprt a1 * pprt b2 + - nprt a2 * nprt b2 + - pprt a1 * pprt b1 + - pprt a2 * nprt b1" by simp  
obua@19404
  2328
  then have "-(- nprt a1 * pprt b2 + - nprt a2 * nprt b2 + - pprt a1 * pprt b1 + - pprt a2 * nprt b1) <= a * b"
obua@19404
  2329
    by (simp only: minus_le_iff)
obua@19404
  2330
  then show ?thesis by simp
obua@15178
  2331
qed
obua@15178
  2332
paulson@14265
  2333
end