src/HOL/Fields.thy
author hoelzl
Fri Oct 24 15:07:51 2014 +0200 (2014-10-24)
changeset 58776 95e58e04e534
parent 58512 dc4d76dfa8f0
child 58826 2ed2eaabe3df
permissions -rw-r--r--
use NO_MATCH-simproc for distribution rules in field_simps, otherwise field_simps on '(a / (c + d)) * (e + f)' can be non-terminating
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(*  Title:      HOL/Fields.thy
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    Author:     Gertrud Bauer
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    Author:     Steven Obua
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    Author:     Tobias Nipkow
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    Author:     Lawrence C Paulson
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    Author:     Markus Wenzel
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    Author:     Jeremy Avigad
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*)
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header {* Fields *}
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theory Fields
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imports Rings
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begin
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subsection {* Division rings *}
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text {*
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  A division ring is like a field, but without the commutativity requirement.
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*}
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class inverse =
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  fixes inverse :: "'a \<Rightarrow> 'a"
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    and divide :: "'a \<Rightarrow> 'a \<Rightarrow> 'a"  (infixl "'/" 70)
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setup {* Sign.add_const_constraint
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  (@{const_name "divide"}, SOME @{typ "'a \<Rightarrow> 'a \<Rightarrow> 'a"}) *}
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context semiring
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begin
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lemma [field_simps]:
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  shows distrib_left_NO_MATCH: "NO_MATCH a (x / y) \<Longrightarrow> a * (b + c) = a * b + a * c"
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    and distrib_right_NO_MATCH: "NO_MATCH c (x / y) \<Longrightarrow> (a + b) * c = a * c + b * c"
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  by (rule distrib_left distrib_right)+
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end
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context ring
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begin
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lemma [field_simps]:
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  shows left_diff_distrib_NO_MATCH: "NO_MATCH c (x / y) \<Longrightarrow> (a - b) * c = a * c - b * c"
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    and right_diff_distrib_NO_MATCH: "NO_MATCH a (x / y) \<Longrightarrow> a * (b - c) = a * b - a * c"
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  by (rule left_diff_distrib right_diff_distrib)+
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end
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setup {* Sign.add_const_constraint
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  (@{const_name "divide"}, SOME @{typ "'a::inverse \<Rightarrow> 'a \<Rightarrow> 'a"}) *}
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text{* Lemmas @{text divide_simps} move division to the outside and eliminates them on (in)equalities. *}
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named_theorems divide_simps "rewrite rules to eliminate divisions"
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class division_ring = ring_1 + inverse +
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  assumes left_inverse [simp]:  "a \<noteq> 0 \<Longrightarrow> inverse a * a = 1"
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  assumes right_inverse [simp]: "a \<noteq> 0 \<Longrightarrow> a * inverse a = 1"
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  assumes divide_inverse: "a / b = a * inverse b"
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begin
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subclass ring_1_no_zero_divisors
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proof
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  fix a b :: 'a
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  assume a: "a \<noteq> 0" and b: "b \<noteq> 0"
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  show "a * b \<noteq> 0"
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  proof
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    assume ab: "a * b = 0"
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    hence "0 = inverse a * (a * b) * inverse b" by simp
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    also have "\<dots> = (inverse a * a) * (b * inverse b)"
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      by (simp only: mult.assoc)
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    also have "\<dots> = 1" using a b by simp
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    finally show False by simp
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  qed
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qed
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lemma nonzero_imp_inverse_nonzero:
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  "a \<noteq> 0 \<Longrightarrow> inverse a \<noteq> 0"
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proof
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  assume ianz: "inverse a = 0"
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  assume "a \<noteq> 0"
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  hence "1 = a * inverse a" by simp
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  also have "... = 0" by (simp add: ianz)
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  finally have "1 = 0" .
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  thus False by (simp add: eq_commute)
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qed
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lemma inverse_zero_imp_zero:
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  "inverse a = 0 \<Longrightarrow> a = 0"
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apply (rule classical)
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apply (drule nonzero_imp_inverse_nonzero)
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apply auto
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done
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lemma inverse_unique: 
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  assumes ab: "a * b = 1"
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  shows "inverse a = b"
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proof -
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  have "a \<noteq> 0" using ab by (cases "a = 0") simp_all
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  moreover have "inverse a * (a * b) = inverse a" by (simp add: ab)
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  ultimately show ?thesis by (simp add: mult.assoc [symmetric])
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qed
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lemma nonzero_inverse_minus_eq:
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  "a \<noteq> 0 \<Longrightarrow> inverse (- a) = - inverse a"
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by (rule inverse_unique) simp
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lemma nonzero_inverse_inverse_eq:
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  "a \<noteq> 0 \<Longrightarrow> inverse (inverse a) = a"
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by (rule inverse_unique) simp
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lemma nonzero_inverse_eq_imp_eq:
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  assumes "inverse a = inverse b" and "a \<noteq> 0" and "b \<noteq> 0"
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  shows "a = b"
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proof -
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  from `inverse a = inverse b`
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  have "inverse (inverse a) = inverse (inverse b)" by (rule arg_cong)
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  with `a \<noteq> 0` and `b \<noteq> 0` show "a = b"
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    by (simp add: nonzero_inverse_inverse_eq)
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qed
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lemma inverse_1 [simp]: "inverse 1 = 1"
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by (rule inverse_unique) simp
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lemma nonzero_inverse_mult_distrib: 
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  assumes "a \<noteq> 0" and "b \<noteq> 0"
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  shows "inverse (a * b) = inverse b * inverse a"
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proof -
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  have "a * (b * inverse b) * inverse a = 1" using assms by simp
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  hence "a * b * (inverse b * inverse a) = 1" by (simp only: mult.assoc)
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  thus ?thesis by (rule inverse_unique)
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qed
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lemma division_ring_inverse_add:
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  "a \<noteq> 0 \<Longrightarrow> b \<noteq> 0 \<Longrightarrow> inverse a + inverse b = inverse a * (a + b) * inverse b"
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by (simp add: algebra_simps)
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lemma division_ring_inverse_diff:
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  "a \<noteq> 0 \<Longrightarrow> b \<noteq> 0 \<Longrightarrow> inverse a - inverse b = inverse a * (b - a) * inverse b"
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by (simp add: algebra_simps)
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lemma right_inverse_eq: "b \<noteq> 0 \<Longrightarrow> a / b = 1 \<longleftrightarrow> a = b"
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proof
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  assume neq: "b \<noteq> 0"
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  {
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    hence "a = (a / b) * b" by (simp add: divide_inverse mult.assoc)
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    also assume "a / b = 1"
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    finally show "a = b" by simp
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  next
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    assume "a = b"
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    with neq show "a / b = 1" by (simp add: divide_inverse)
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  }
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qed
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lemma nonzero_inverse_eq_divide: "a \<noteq> 0 \<Longrightarrow> inverse a = 1 / a"
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by (simp add: divide_inverse)
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lemma divide_self [simp]: "a \<noteq> 0 \<Longrightarrow> a / a = 1"
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by (simp add: divide_inverse)
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lemma divide_zero_left [simp]: "0 / a = 0"
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by (simp add: divide_inverse)
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lemma inverse_eq_divide [field_simps, divide_simps]: "inverse a = 1 / a"
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by (simp add: divide_inverse)
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lemma add_divide_distrib: "(a+b) / c = a/c + b/c"
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by (simp add: divide_inverse algebra_simps)
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lemma divide_1 [simp]: "a / 1 = a"
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  by (simp add: divide_inverse)
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lemma times_divide_eq_right [simp]: "a * (b / c) = (a * b) / c"
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  by (simp add: divide_inverse mult.assoc)
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lemma minus_divide_left: "- (a / b) = (-a) / b"
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  by (simp add: divide_inverse)
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lemma nonzero_minus_divide_right: "b \<noteq> 0 ==> - (a / b) = a / (- b)"
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  by (simp add: divide_inverse nonzero_inverse_minus_eq)
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lemma nonzero_minus_divide_divide: "b \<noteq> 0 ==> (-a) / (-b) = a / b"
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  by (simp add: divide_inverse nonzero_inverse_minus_eq)
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lemma divide_minus_left [simp]: "(-a) / b = - (a / b)"
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  by (simp add: divide_inverse)
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lemma diff_divide_distrib: "(a - b) / c = a / c - b / c"
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  using add_divide_distrib [of a "- b" c] by simp
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lemma nonzero_eq_divide_eq [field_simps]: "c \<noteq> 0 \<Longrightarrow> a = b / c \<longleftrightarrow> a * c = b"
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proof -
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  assume [simp]: "c \<noteq> 0"
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  have "a = b / c \<longleftrightarrow> a * c = (b / c) * c" by simp
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  also have "... \<longleftrightarrow> a * c = b" by (simp add: divide_inverse mult.assoc)
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  finally show ?thesis .
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qed
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lemma nonzero_divide_eq_eq [field_simps]: "c \<noteq> 0 \<Longrightarrow> b / c = a \<longleftrightarrow> b = a * c"
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proof -
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  assume [simp]: "c \<noteq> 0"
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  have "b / c = a \<longleftrightarrow> (b / c) * c = a * c" by simp
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  also have "... \<longleftrightarrow> b = a * c" by (simp add: divide_inverse mult.assoc) 
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  finally show ?thesis .
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qed
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lemma nonzero_neg_divide_eq_eq [field_simps]: "b \<noteq> 0 \<Longrightarrow> - (a / b) = c \<longleftrightarrow> - a = c * b"
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  using nonzero_divide_eq_eq[of b "-a" c] by (simp add: divide_minus_left)
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lemma nonzero_neg_divide_eq_eq2 [field_simps]: "b \<noteq> 0 \<Longrightarrow> c = - (a / b) \<longleftrightarrow> c * b = - a"
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  using nonzero_neg_divide_eq_eq[of b a c] by auto
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lemma divide_eq_imp: "c \<noteq> 0 \<Longrightarrow> b = a * c \<Longrightarrow> b / c = a"
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  by (simp add: divide_inverse mult.assoc)
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lemma eq_divide_imp: "c \<noteq> 0 \<Longrightarrow> a * c = b \<Longrightarrow> a = b / c"
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  by (drule sym) (simp add: divide_inverse mult.assoc)
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lemma add_divide_eq_iff [field_simps]:
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  "z \<noteq> 0 \<Longrightarrow> x + y / z = (x * z + y) / z"
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  by (simp add: add_divide_distrib nonzero_eq_divide_eq)
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lemma divide_add_eq_iff [field_simps]:
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  "z \<noteq> 0 \<Longrightarrow> x / z + y = (x + y * z) / z"
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  by (simp add: add_divide_distrib nonzero_eq_divide_eq)
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lemma diff_divide_eq_iff [field_simps]:
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  "z \<noteq> 0 \<Longrightarrow> x - y / z = (x * z - y) / z"
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  by (simp add: diff_divide_distrib nonzero_eq_divide_eq eq_diff_eq)
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lemma minus_divide_add_eq_iff [field_simps]:
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  "z \<noteq> 0 \<Longrightarrow> - (x / z) + y = (- x + y * z) / z"
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  by (simp add: add_divide_distrib diff_divide_eq_iff divide_minus_left)
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lemma divide_diff_eq_iff [field_simps]:
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  "z \<noteq> 0 \<Longrightarrow> x / z - y = (x - y * z) / z"
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  by (simp add: field_simps)
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lemma minus_divide_diff_eq_iff [field_simps]:
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  "z \<noteq> 0 \<Longrightarrow> - (x / z) - y = (- x - y * z) / z"
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  by (simp add: divide_diff_eq_iff[symmetric] divide_minus_left)
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end
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class division_ring_inverse_zero = division_ring +
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  assumes inverse_zero [simp]: "inverse 0 = 0"
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begin
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lemma divide_zero [simp]:
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  "a / 0 = 0"
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  by (simp add: divide_inverse)
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lemma divide_self_if [simp]:
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  "a / a = (if a = 0 then 0 else 1)"
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  by simp
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lemma inverse_nonzero_iff_nonzero [simp]:
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  "inverse a = 0 \<longleftrightarrow> a = 0"
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  by rule (fact inverse_zero_imp_zero, simp)
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lemma inverse_minus_eq [simp]:
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  "inverse (- a) = - inverse a"
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proof cases
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  assume "a=0" thus ?thesis by simp
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next
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  assume "a\<noteq>0" 
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  thus ?thesis by (simp add: nonzero_inverse_minus_eq)
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qed
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lemma inverse_inverse_eq [simp]:
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  "inverse (inverse a) = a"
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proof cases
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  assume "a=0" thus ?thesis by simp
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next
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  assume "a\<noteq>0" 
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  thus ?thesis by (simp add: nonzero_inverse_inverse_eq)
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qed
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lemma inverse_eq_imp_eq:
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  "inverse a = inverse b \<Longrightarrow> a = b"
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  by (drule arg_cong [where f="inverse"], simp)
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lemma inverse_eq_iff_eq [simp]:
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  "inverse a = inverse b \<longleftrightarrow> a = b"
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  by (force dest!: inverse_eq_imp_eq)
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lemma add_divide_eq_if_simps [divide_simps]:
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    "a + b / z = (if z = 0 then a else (a * z + b) / z)"
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    "a / z + b = (if z = 0 then b else (a + b * z) / z)"
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    "- (a / z) + b = (if z = 0 then b else (-a + b * z) / z)"
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    "a - b / z = (if z = 0 then a else (a * z - b) / z)"
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    "a / z - b = (if z = 0 then -b else (a - b * z) / z)"
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    "- (a / z) - b = (if z = 0 then -b else (- a - b * z) / z)"
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  by (simp_all add: add_divide_eq_iff divide_add_eq_iff diff_divide_eq_iff divide_diff_eq_iff
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      minus_divide_diff_eq_iff)
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lemma [divide_simps]:
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  shows divide_eq_eq: "b / c = a \<longleftrightarrow> (if c \<noteq> 0 then b = a * c else a = 0)"
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    and eq_divide_eq: "a = b / c \<longleftrightarrow> (if c \<noteq> 0 then a * c = b else a = 0)"
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    and minus_divide_eq_eq: "- (b / c) = a \<longleftrightarrow> (if c \<noteq> 0 then - b = a * c else a = 0)"
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    and eq_minus_divide_eq: "a = - (b / c) \<longleftrightarrow> (if c \<noteq> 0 then a * c = - b else a = 0)"
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  by (auto simp add:  field_simps)
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end
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subsection {* Fields *}
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class field = comm_ring_1 + inverse +
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  assumes field_inverse: "a \<noteq> 0 \<Longrightarrow> inverse a * a = 1"
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  assumes field_divide_inverse: "a / b = a * inverse b"
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begin
huffman@20496
   313
haftmann@25267
   314
subclass division_ring
haftmann@28823
   315
proof
huffman@22987
   316
  fix a :: 'a
huffman@22987
   317
  assume "a \<noteq> 0"
huffman@22987
   318
  thus "inverse a * a = 1" by (rule field_inverse)
haftmann@57512
   319
  thus "a * inverse a = 1" by (simp only: mult.commute)
haftmann@35084
   320
next
haftmann@35084
   321
  fix a b :: 'a
haftmann@35084
   322
  show "a / b = a * inverse b" by (rule field_divide_inverse)
obua@14738
   323
qed
haftmann@25230
   324
huffman@27516
   325
subclass idom ..
haftmann@25230
   326
huffman@30630
   327
text{*There is no slick version using division by zero.*}
huffman@30630
   328
lemma inverse_add:
huffman@30630
   329
  "[| a \<noteq> 0;  b \<noteq> 0 |]
huffman@30630
   330
   ==> inverse a + inverse b = (a + b) * inverse a * inverse b"
haftmann@57514
   331
by (simp add: division_ring_inverse_add ac_simps)
huffman@30630
   332
blanchet@54147
   333
lemma nonzero_mult_divide_mult_cancel_left [simp]:
huffman@30630
   334
assumes [simp]: "b\<noteq>0" and [simp]: "c\<noteq>0" shows "(c*a)/(c*b) = a/b"
huffman@30630
   335
proof -
huffman@30630
   336
  have "(c*a)/(c*b) = c * a * (inverse b * inverse c)"
huffman@30630
   337
    by (simp add: divide_inverse nonzero_inverse_mult_distrib)
huffman@30630
   338
  also have "... =  a * inverse b * (inverse c * c)"
haftmann@57514
   339
    by (simp only: ac_simps)
huffman@30630
   340
  also have "... =  a * inverse b" by simp
huffman@30630
   341
    finally show ?thesis by (simp add: divide_inverse)
huffman@30630
   342
qed
huffman@30630
   343
blanchet@54147
   344
lemma nonzero_mult_divide_mult_cancel_right [simp]:
huffman@30630
   345
  "\<lbrakk>b \<noteq> 0; c \<noteq> 0\<rbrakk> \<Longrightarrow> (a * c) / (b * c) = a / b"
haftmann@57512
   346
by (simp add: mult.commute [of _ c])
huffman@30630
   347
haftmann@36304
   348
lemma times_divide_eq_left [simp]: "(b / c) * a = (b * a) / c"
haftmann@57514
   349
  by (simp add: divide_inverse ac_simps)
huffman@30630
   350
huffman@44921
   351
text{*It's not obvious whether @{text times_divide_eq} should be
huffman@44921
   352
  simprules or not. Their effect is to gather terms into one big
huffman@44921
   353
  fraction, like a*b*c / x*y*z. The rationale for that is unclear, but
huffman@44921
   354
  many proofs seem to need them.*}
huffman@44921
   355
blanchet@54147
   356
lemmas times_divide_eq = times_divide_eq_right times_divide_eq_left
huffman@30630
   357
huffman@30630
   358
lemma add_frac_eq:
huffman@30630
   359
  assumes "y \<noteq> 0" and "z \<noteq> 0"
huffman@30630
   360
  shows "x / y + w / z = (x * z + w * y) / (y * z)"
huffman@30630
   361
proof -
huffman@30630
   362
  have "x / y + w / z = (x * z) / (y * z) + (y * w) / (y * z)"
huffman@30630
   363
    using assms by simp
huffman@30630
   364
  also have "\<dots> = (x * z + y * w) / (y * z)"
huffman@30630
   365
    by (simp only: add_divide_distrib)
huffman@30630
   366
  finally show ?thesis
haftmann@57512
   367
    by (simp only: mult.commute)
huffman@30630
   368
qed
huffman@30630
   369
huffman@30630
   370
text{*Special Cancellation Simprules for Division*}
huffman@30630
   371
blanchet@54147
   372
lemma nonzero_mult_divide_cancel_right [simp]:
huffman@30630
   373
  "b \<noteq> 0 \<Longrightarrow> a * b / b = a"
haftmann@36301
   374
  using nonzero_mult_divide_mult_cancel_right [of 1 b a] by simp
huffman@30630
   375
blanchet@54147
   376
lemma nonzero_mult_divide_cancel_left [simp]:
huffman@30630
   377
  "a \<noteq> 0 \<Longrightarrow> a * b / a = b"
huffman@30630
   378
using nonzero_mult_divide_mult_cancel_left [of 1 a b] by simp
huffman@30630
   379
blanchet@54147
   380
lemma nonzero_divide_mult_cancel_right [simp]:
huffman@30630
   381
  "\<lbrakk>a \<noteq> 0; b \<noteq> 0\<rbrakk> \<Longrightarrow> b / (a * b) = 1 / a"
huffman@30630
   382
using nonzero_mult_divide_mult_cancel_right [of a b 1] by simp
huffman@30630
   383
blanchet@54147
   384
lemma nonzero_divide_mult_cancel_left [simp]:
huffman@30630
   385
  "\<lbrakk>a \<noteq> 0; b \<noteq> 0\<rbrakk> \<Longrightarrow> a / (a * b) = 1 / b"
huffman@30630
   386
using nonzero_mult_divide_mult_cancel_left [of b a 1] by simp
huffman@30630
   387
blanchet@54147
   388
lemma nonzero_mult_divide_mult_cancel_left2 [simp]:
huffman@30630
   389
  "\<lbrakk>b \<noteq> 0; c \<noteq> 0\<rbrakk> \<Longrightarrow> (c * a) / (b * c) = a / b"
haftmann@57514
   390
using nonzero_mult_divide_mult_cancel_left [of b c a] by (simp add: ac_simps)
huffman@30630
   391
blanchet@54147
   392
lemma nonzero_mult_divide_mult_cancel_right2 [simp]:
huffman@30630
   393
  "\<lbrakk>b \<noteq> 0; c \<noteq> 0\<rbrakk> \<Longrightarrow> (a * c) / (c * b) = a / b"
haftmann@57514
   394
using nonzero_mult_divide_mult_cancel_right [of b c a] by (simp add: ac_simps)
huffman@30630
   395
huffman@30630
   396
lemma diff_frac_eq:
huffman@30630
   397
  "y \<noteq> 0 \<Longrightarrow> z \<noteq> 0 \<Longrightarrow> x / y - w / z = (x * z - w * y) / (y * z)"
haftmann@36348
   398
  by (simp add: field_simps)
huffman@30630
   399
huffman@30630
   400
lemma frac_eq_eq:
huffman@30630
   401
  "y \<noteq> 0 \<Longrightarrow> z \<noteq> 0 \<Longrightarrow> (x / y = w / z) = (x * z = w * y)"
haftmann@36348
   402
  by (simp add: field_simps)
haftmann@36348
   403
haftmann@58512
   404
lemma divide_minus1 [simp]: "x / - 1 = - x"
haftmann@58512
   405
  using nonzero_minus_divide_right [of "1" x] by simp
haftmann@58512
   406
  
haftmann@36348
   407
end
haftmann@36348
   408
haftmann@36348
   409
class field_inverse_zero = field +
haftmann@36348
   410
  assumes field_inverse_zero: "inverse 0 = 0"
haftmann@36348
   411
begin
haftmann@36348
   412
haftmann@36348
   413
subclass division_ring_inverse_zero proof
haftmann@36348
   414
qed (fact field_inverse_zero)
haftmann@25230
   415
paulson@14270
   416
text{*This version builds in division by zero while also re-orienting
paulson@14270
   417
      the right-hand side.*}
paulson@14270
   418
lemma inverse_mult_distrib [simp]:
haftmann@36409
   419
  "inverse (a * b) = inverse a * inverse b"
haftmann@36409
   420
proof cases
haftmann@36409
   421
  assume "a \<noteq> 0 & b \<noteq> 0" 
haftmann@57514
   422
  thus ?thesis by (simp add: nonzero_inverse_mult_distrib ac_simps)
haftmann@36409
   423
next
haftmann@36409
   424
  assume "~ (a \<noteq> 0 & b \<noteq> 0)" 
haftmann@36409
   425
  thus ?thesis by force
haftmann@36409
   426
qed
paulson@14270
   427
paulson@14365
   428
lemma inverse_divide [simp]:
haftmann@36409
   429
  "inverse (a / b) = b / a"
haftmann@57512
   430
  by (simp add: divide_inverse mult.commute)
paulson@14365
   431
wenzelm@23389
   432
haftmann@36301
   433
text {* Calculations with fractions *}
avigad@16775
   434
nipkow@23413
   435
text{* There is a whole bunch of simp-rules just for class @{text
nipkow@23413
   436
field} but none for class @{text field} and @{text nonzero_divides}
nipkow@23413
   437
because the latter are covered by a simproc. *}
nipkow@23413
   438
nipkow@23413
   439
lemma mult_divide_mult_cancel_left:
haftmann@36409
   440
  "c \<noteq> 0 \<Longrightarrow> (c * a) / (c * b) = a / b"
haftmann@21328
   441
apply (cases "b = 0")
huffman@35216
   442
apply simp_all
paulson@14277
   443
done
paulson@14277
   444
nipkow@23413
   445
lemma mult_divide_mult_cancel_right:
haftmann@36409
   446
  "c \<noteq> 0 \<Longrightarrow> (a * c) / (b * c) = a / b"
haftmann@21328
   447
apply (cases "b = 0")
huffman@35216
   448
apply simp_all
paulson@14321
   449
done
nipkow@23413
   450
blanchet@54147
   451
lemma divide_divide_eq_right [simp]:
haftmann@36409
   452
  "a / (b / c) = (a * c) / b"
haftmann@57514
   453
  by (simp add: divide_inverse ac_simps)
paulson@14288
   454
blanchet@54147
   455
lemma divide_divide_eq_left [simp]:
haftmann@36409
   456
  "(a / b) / c = a / (b * c)"
haftmann@57512
   457
  by (simp add: divide_inverse mult.assoc)
paulson@14288
   458
lp15@56365
   459
lemma divide_divide_times_eq:
lp15@56365
   460
  "(x / y) / (z / w) = (x * w) / (y * z)"
lp15@56365
   461
  by simp
wenzelm@23389
   462
haftmann@36301
   463
text {*Special Cancellation Simprules for Division*}
paulson@15234
   464
blanchet@54147
   465
lemma mult_divide_mult_cancel_left_if [simp]:
haftmann@36409
   466
  shows "(c * a) / (c * b) = (if c = 0 then 0 else a / b)"
haftmann@36409
   467
  by (simp add: mult_divide_mult_cancel_left)
nipkow@23413
   468
paulson@15234
   469
haftmann@36301
   470
text {* Division and Unary Minus *}
paulson@14293
   471
haftmann@36409
   472
lemma minus_divide_right:
haftmann@36409
   473
  "- (a / b) = a / - b"
haftmann@36409
   474
  by (simp add: divide_inverse)
paulson@14430
   475
hoelzl@56479
   476
lemma divide_minus_right [simp]:
haftmann@36409
   477
  "a / - b = - (a / b)"
haftmann@36409
   478
  by (simp add: divide_inverse)
huffman@30630
   479
hoelzl@56479
   480
lemma minus_divide_divide:
haftmann@36409
   481
  "(- a) / (- b) = a / b"
haftmann@21328
   482
apply (cases "b=0", simp) 
paulson@14293
   483
apply (simp add: nonzero_minus_divide_divide) 
paulson@14293
   484
done
paulson@14293
   485
haftmann@36301
   486
lemma inverse_eq_1_iff [simp]:
haftmann@36409
   487
  "inverse x = 1 \<longleftrightarrow> x = 1"
haftmann@36409
   488
  by (insert inverse_eq_iff_eq [of x 1], simp) 
wenzelm@23389
   489
blanchet@54147
   490
lemma divide_eq_0_iff [simp]:
haftmann@36409
   491
  "a / b = 0 \<longleftrightarrow> a = 0 \<or> b = 0"
haftmann@36409
   492
  by (simp add: divide_inverse)
haftmann@36301
   493
blanchet@54147
   494
lemma divide_cancel_right [simp]:
haftmann@36409
   495
  "a / c = b / c \<longleftrightarrow> c = 0 \<or> a = b"
haftmann@36409
   496
  apply (cases "c=0", simp)
haftmann@36409
   497
  apply (simp add: divide_inverse)
haftmann@36409
   498
  done
haftmann@36301
   499
blanchet@54147
   500
lemma divide_cancel_left [simp]:
haftmann@36409
   501
  "c / a = c / b \<longleftrightarrow> c = 0 \<or> a = b" 
haftmann@36409
   502
  apply (cases "c=0", simp)
haftmann@36409
   503
  apply (simp add: divide_inverse)
haftmann@36409
   504
  done
haftmann@36301
   505
blanchet@54147
   506
lemma divide_eq_1_iff [simp]:
haftmann@36409
   507
  "a / b = 1 \<longleftrightarrow> b \<noteq> 0 \<and> a = b"
haftmann@36409
   508
  apply (cases "b=0", simp)
haftmann@36409
   509
  apply (simp add: right_inverse_eq)
haftmann@36409
   510
  done
haftmann@36301
   511
blanchet@54147
   512
lemma one_eq_divide_iff [simp]:
haftmann@36409
   513
  "1 = a / b \<longleftrightarrow> b \<noteq> 0 \<and> a = b"
haftmann@36409
   514
  by (simp add: eq_commute [of 1])
haftmann@36409
   515
haftmann@36719
   516
lemma times_divide_times_eq:
haftmann@36719
   517
  "(x / y) * (z / w) = (x * z) / (y * w)"
haftmann@36719
   518
  by simp
haftmann@36719
   519
haftmann@36719
   520
lemma add_frac_num:
haftmann@36719
   521
  "y \<noteq> 0 \<Longrightarrow> x / y + z = (x + z * y) / y"
haftmann@36719
   522
  by (simp add: add_divide_distrib)
haftmann@36719
   523
haftmann@36719
   524
lemma add_num_frac:
haftmann@36719
   525
  "y \<noteq> 0 \<Longrightarrow> z + x / y = (x + z * y) / y"
haftmann@36719
   526
  by (simp add: add_divide_distrib add.commute)
haftmann@36719
   527
haftmann@36409
   528
end
haftmann@36301
   529
haftmann@36301
   530
huffman@44064
   531
subsection {* Ordered fields *}
haftmann@36301
   532
haftmann@36301
   533
class linordered_field = field + linordered_idom
haftmann@36301
   534
begin
paulson@14268
   535
paulson@14277
   536
lemma positive_imp_inverse_positive: 
haftmann@36301
   537
  assumes a_gt_0: "0 < a" 
haftmann@36301
   538
  shows "0 < inverse a"
nipkow@23482
   539
proof -
paulson@14268
   540
  have "0 < a * inverse a" 
haftmann@36301
   541
    by (simp add: a_gt_0 [THEN less_imp_not_eq2])
paulson@14268
   542
  thus "0 < inverse a" 
haftmann@36301
   543
    by (simp add: a_gt_0 [THEN less_not_sym] zero_less_mult_iff)
nipkow@23482
   544
qed
paulson@14268
   545
paulson@14277
   546
lemma negative_imp_inverse_negative:
haftmann@36301
   547
  "a < 0 \<Longrightarrow> inverse a < 0"
haftmann@36301
   548
  by (insert positive_imp_inverse_positive [of "-a"], 
haftmann@36301
   549
    simp add: nonzero_inverse_minus_eq less_imp_not_eq)
paulson@14268
   550
paulson@14268
   551
lemma inverse_le_imp_le:
haftmann@36301
   552
  assumes invle: "inverse a \<le> inverse b" and apos: "0 < a"
haftmann@36301
   553
  shows "b \<le> a"
nipkow@23482
   554
proof (rule classical)
paulson@14268
   555
  assume "~ b \<le> a"
nipkow@23482
   556
  hence "a < b"  by (simp add: linorder_not_le)
haftmann@36301
   557
  hence bpos: "0 < b"  by (blast intro: apos less_trans)
paulson@14268
   558
  hence "a * inverse a \<le> a * inverse b"
haftmann@36301
   559
    by (simp add: apos invle less_imp_le mult_left_mono)
paulson@14268
   560
  hence "(a * inverse a) * b \<le> (a * inverse b) * b"
haftmann@36301
   561
    by (simp add: bpos less_imp_le mult_right_mono)
haftmann@57512
   562
  thus "b \<le> a"  by (simp add: mult.assoc apos bpos less_imp_not_eq2)
nipkow@23482
   563
qed
paulson@14268
   564
paulson@14277
   565
lemma inverse_positive_imp_positive:
haftmann@36301
   566
  assumes inv_gt_0: "0 < inverse a" and nz: "a \<noteq> 0"
haftmann@36301
   567
  shows "0 < a"
wenzelm@23389
   568
proof -
paulson@14277
   569
  have "0 < inverse (inverse a)"
wenzelm@23389
   570
    using inv_gt_0 by (rule positive_imp_inverse_positive)
paulson@14277
   571
  thus "0 < a"
wenzelm@23389
   572
    using nz by (simp add: nonzero_inverse_inverse_eq)
wenzelm@23389
   573
qed
paulson@14277
   574
haftmann@36301
   575
lemma inverse_negative_imp_negative:
haftmann@36301
   576
  assumes inv_less_0: "inverse a < 0" and nz: "a \<noteq> 0"
haftmann@36301
   577
  shows "a < 0"
haftmann@36301
   578
proof -
haftmann@36301
   579
  have "inverse (inverse a) < 0"
haftmann@36301
   580
    using inv_less_0 by (rule negative_imp_inverse_negative)
haftmann@36301
   581
  thus "a < 0" using nz by (simp add: nonzero_inverse_inverse_eq)
haftmann@36301
   582
qed
haftmann@36301
   583
haftmann@36301
   584
lemma linordered_field_no_lb:
haftmann@36301
   585
  "\<forall>x. \<exists>y. y < x"
haftmann@36301
   586
proof
haftmann@36301
   587
  fix x::'a
haftmann@36301
   588
  have m1: "- (1::'a) < 0" by simp
haftmann@36301
   589
  from add_strict_right_mono[OF m1, where c=x] 
haftmann@36301
   590
  have "(- 1) + x < x" by simp
haftmann@36301
   591
  thus "\<exists>y. y < x" by blast
haftmann@36301
   592
qed
haftmann@36301
   593
haftmann@36301
   594
lemma linordered_field_no_ub:
haftmann@36301
   595
  "\<forall> x. \<exists>y. y > x"
haftmann@36301
   596
proof
haftmann@36301
   597
  fix x::'a
haftmann@36301
   598
  have m1: " (1::'a) > 0" by simp
haftmann@36301
   599
  from add_strict_right_mono[OF m1, where c=x] 
haftmann@36301
   600
  have "1 + x > x" by simp
haftmann@36301
   601
  thus "\<exists>y. y > x" by blast
haftmann@36301
   602
qed
haftmann@36301
   603
haftmann@36301
   604
lemma less_imp_inverse_less:
haftmann@36301
   605
  assumes less: "a < b" and apos:  "0 < a"
haftmann@36301
   606
  shows "inverse b < inverse a"
haftmann@36301
   607
proof (rule ccontr)
haftmann@36301
   608
  assume "~ inverse b < inverse a"
haftmann@36301
   609
  hence "inverse a \<le> inverse b" by simp
haftmann@36301
   610
  hence "~ (a < b)"
haftmann@36301
   611
    by (simp add: not_less inverse_le_imp_le [OF _ apos])
haftmann@36301
   612
  thus False by (rule notE [OF _ less])
haftmann@36301
   613
qed
haftmann@36301
   614
haftmann@36301
   615
lemma inverse_less_imp_less:
haftmann@36301
   616
  "inverse a < inverse b \<Longrightarrow> 0 < a \<Longrightarrow> b < a"
haftmann@36301
   617
apply (simp add: less_le [of "inverse a"] less_le [of "b"])
haftmann@36301
   618
apply (force dest!: inverse_le_imp_le nonzero_inverse_eq_imp_eq) 
haftmann@36301
   619
done
haftmann@36301
   620
haftmann@36301
   621
text{*Both premises are essential. Consider -1 and 1.*}
blanchet@54147
   622
lemma inverse_less_iff_less [simp]:
haftmann@36301
   623
  "0 < a \<Longrightarrow> 0 < b \<Longrightarrow> inverse a < inverse b \<longleftrightarrow> b < a"
haftmann@36301
   624
  by (blast intro: less_imp_inverse_less dest: inverse_less_imp_less) 
haftmann@36301
   625
haftmann@36301
   626
lemma le_imp_inverse_le:
haftmann@36301
   627
  "a \<le> b \<Longrightarrow> 0 < a \<Longrightarrow> inverse b \<le> inverse a"
haftmann@36301
   628
  by (force simp add: le_less less_imp_inverse_less)
haftmann@36301
   629
blanchet@54147
   630
lemma inverse_le_iff_le [simp]:
haftmann@36301
   631
  "0 < a \<Longrightarrow> 0 < b \<Longrightarrow> inverse a \<le> inverse b \<longleftrightarrow> b \<le> a"
haftmann@36301
   632
  by (blast intro: le_imp_inverse_le dest: inverse_le_imp_le) 
haftmann@36301
   633
haftmann@36301
   634
haftmann@36301
   635
text{*These results refer to both operands being negative.  The opposite-sign
haftmann@36301
   636
case is trivial, since inverse preserves signs.*}
haftmann@36301
   637
lemma inverse_le_imp_le_neg:
haftmann@36301
   638
  "inverse a \<le> inverse b \<Longrightarrow> b < 0 \<Longrightarrow> b \<le> a"
haftmann@36301
   639
apply (rule classical) 
haftmann@36301
   640
apply (subgoal_tac "a < 0") 
haftmann@36301
   641
 prefer 2 apply force
haftmann@36301
   642
apply (insert inverse_le_imp_le [of "-b" "-a"])
haftmann@36301
   643
apply (simp add: nonzero_inverse_minus_eq) 
haftmann@36301
   644
done
haftmann@36301
   645
haftmann@36301
   646
lemma less_imp_inverse_less_neg:
haftmann@36301
   647
   "a < b \<Longrightarrow> b < 0 \<Longrightarrow> inverse b < inverse a"
haftmann@36301
   648
apply (subgoal_tac "a < 0") 
haftmann@36301
   649
 prefer 2 apply (blast intro: less_trans) 
haftmann@36301
   650
apply (insert less_imp_inverse_less [of "-b" "-a"])
haftmann@36301
   651
apply (simp add: nonzero_inverse_minus_eq) 
haftmann@36301
   652
done
haftmann@36301
   653
haftmann@36301
   654
lemma inverse_less_imp_less_neg:
haftmann@36301
   655
   "inverse a < inverse b \<Longrightarrow> b < 0 \<Longrightarrow> b < a"
haftmann@36301
   656
apply (rule classical) 
haftmann@36301
   657
apply (subgoal_tac "a < 0") 
haftmann@36301
   658
 prefer 2
haftmann@36301
   659
 apply force
haftmann@36301
   660
apply (insert inverse_less_imp_less [of "-b" "-a"])
haftmann@36301
   661
apply (simp add: nonzero_inverse_minus_eq) 
haftmann@36301
   662
done
haftmann@36301
   663
blanchet@54147
   664
lemma inverse_less_iff_less_neg [simp]:
haftmann@36301
   665
  "a < 0 \<Longrightarrow> b < 0 \<Longrightarrow> inverse a < inverse b \<longleftrightarrow> b < a"
haftmann@36301
   666
apply (insert inverse_less_iff_less [of "-b" "-a"])
haftmann@36301
   667
apply (simp del: inverse_less_iff_less 
haftmann@36301
   668
            add: nonzero_inverse_minus_eq)
haftmann@36301
   669
done
haftmann@36301
   670
haftmann@36301
   671
lemma le_imp_inverse_le_neg:
haftmann@36301
   672
  "a \<le> b \<Longrightarrow> b < 0 ==> inverse b \<le> inverse a"
haftmann@36301
   673
  by (force simp add: le_less less_imp_inverse_less_neg)
haftmann@36301
   674
blanchet@54147
   675
lemma inverse_le_iff_le_neg [simp]:
haftmann@36301
   676
  "a < 0 \<Longrightarrow> b < 0 \<Longrightarrow> inverse a \<le> inverse b \<longleftrightarrow> b \<le> a"
haftmann@36301
   677
  by (blast intro: le_imp_inverse_le_neg dest: inverse_le_imp_le_neg) 
haftmann@36301
   678
huffman@36774
   679
lemma one_less_inverse:
huffman@36774
   680
  "0 < a \<Longrightarrow> a < 1 \<Longrightarrow> 1 < inverse a"
huffman@36774
   681
  using less_imp_inverse_less [of a 1, unfolded inverse_1] .
huffman@36774
   682
huffman@36774
   683
lemma one_le_inverse:
huffman@36774
   684
  "0 < a \<Longrightarrow> a \<le> 1 \<Longrightarrow> 1 \<le> inverse a"
huffman@36774
   685
  using le_imp_inverse_le [of a 1, unfolded inverse_1] .
huffman@36774
   686
hoelzl@56480
   687
lemma pos_le_divide_eq [field_simps]: "0 < c \<Longrightarrow> a \<le> b / c \<longleftrightarrow> a * c \<le> b"
haftmann@36301
   688
proof -
haftmann@36301
   689
  assume less: "0<c"
haftmann@36301
   690
  hence "(a \<le> b/c) = (a*c \<le> (b/c)*c)"
haftmann@36304
   691
    by (simp add: mult_le_cancel_right less_not_sym [OF less] del: times_divide_eq)
haftmann@36301
   692
  also have "... = (a*c \<le> b)"
haftmann@57512
   693
    by (simp add: less_imp_not_eq2 [OF less] divide_inverse mult.assoc) 
haftmann@36301
   694
  finally show ?thesis .
haftmann@36301
   695
qed
haftmann@36301
   696
hoelzl@56480
   697
lemma neg_le_divide_eq [field_simps]: "c < 0 \<Longrightarrow> a \<le> b / c \<longleftrightarrow> b \<le> a * c"
haftmann@36301
   698
proof -
haftmann@36301
   699
  assume less: "c<0"
haftmann@36301
   700
  hence "(a \<le> b/c) = ((b/c)*c \<le> a*c)"
haftmann@36304
   701
    by (simp add: mult_le_cancel_right less_not_sym [OF less] del: times_divide_eq)
haftmann@36301
   702
  also have "... = (b \<le> a*c)"
haftmann@57512
   703
    by (simp add: less_imp_not_eq [OF less] divide_inverse mult.assoc) 
haftmann@36301
   704
  finally show ?thesis .
haftmann@36301
   705
qed
haftmann@36301
   706
hoelzl@56480
   707
lemma pos_less_divide_eq [field_simps]: "0 < c \<Longrightarrow> a < b / c \<longleftrightarrow> a * c < b"
haftmann@36301
   708
proof -
haftmann@36301
   709
  assume less: "0<c"
haftmann@36301
   710
  hence "(a < b/c) = (a*c < (b/c)*c)"
haftmann@36304
   711
    by (simp add: mult_less_cancel_right_disj less_not_sym [OF less] del: times_divide_eq)
haftmann@36301
   712
  also have "... = (a*c < b)"
haftmann@57512
   713
    by (simp add: less_imp_not_eq2 [OF less] divide_inverse mult.assoc) 
haftmann@36301
   714
  finally show ?thesis .
haftmann@36301
   715
qed
haftmann@36301
   716
hoelzl@56480
   717
lemma neg_less_divide_eq [field_simps]: "c < 0 \<Longrightarrow> a < b / c \<longleftrightarrow> b < a * c"
haftmann@36301
   718
proof -
haftmann@36301
   719
  assume less: "c<0"
haftmann@36301
   720
  hence "(a < b/c) = ((b/c)*c < a*c)"
haftmann@36304
   721
    by (simp add: mult_less_cancel_right_disj less_not_sym [OF less] del: times_divide_eq)
haftmann@36301
   722
  also have "... = (b < a*c)"
haftmann@57512
   723
    by (simp add: less_imp_not_eq [OF less] divide_inverse mult.assoc) 
haftmann@36301
   724
  finally show ?thesis .
haftmann@36301
   725
qed
haftmann@36301
   726
hoelzl@56480
   727
lemma pos_divide_less_eq [field_simps]: "0 < c \<Longrightarrow> b / c < a \<longleftrightarrow> b < a * c"
haftmann@36301
   728
proof -
haftmann@36301
   729
  assume less: "0<c"
haftmann@36301
   730
  hence "(b/c < a) = ((b/c)*c < a*c)"
haftmann@36304
   731
    by (simp add: mult_less_cancel_right_disj less_not_sym [OF less] del: times_divide_eq)
haftmann@36301
   732
  also have "... = (b < a*c)"
haftmann@57512
   733
    by (simp add: less_imp_not_eq2 [OF less] divide_inverse mult.assoc) 
haftmann@36301
   734
  finally show ?thesis .
haftmann@36301
   735
qed
haftmann@36301
   736
hoelzl@56480
   737
lemma neg_divide_less_eq [field_simps]: "c < 0 \<Longrightarrow> b / c < a \<longleftrightarrow> a * c < b"
haftmann@36301
   738
proof -
haftmann@36301
   739
  assume less: "c<0"
haftmann@36301
   740
  hence "(b/c < a) = (a*c < (b/c)*c)"
haftmann@36304
   741
    by (simp add: mult_less_cancel_right_disj less_not_sym [OF less] del: times_divide_eq)
haftmann@36301
   742
  also have "... = (a*c < b)"
haftmann@57512
   743
    by (simp add: less_imp_not_eq [OF less] divide_inverse mult.assoc) 
haftmann@36301
   744
  finally show ?thesis .
haftmann@36301
   745
qed
haftmann@36301
   746
hoelzl@56480
   747
lemma pos_divide_le_eq [field_simps]: "0 < c \<Longrightarrow> b / c \<le> a \<longleftrightarrow> b \<le> a * c"
haftmann@36301
   748
proof -
haftmann@36301
   749
  assume less: "0<c"
haftmann@36301
   750
  hence "(b/c \<le> a) = ((b/c)*c \<le> a*c)"
haftmann@36304
   751
    by (simp add: mult_le_cancel_right less_not_sym [OF less] del: times_divide_eq)
haftmann@36301
   752
  also have "... = (b \<le> a*c)"
haftmann@57512
   753
    by (simp add: less_imp_not_eq2 [OF less] divide_inverse mult.assoc) 
haftmann@36301
   754
  finally show ?thesis .
haftmann@36301
   755
qed
haftmann@36301
   756
hoelzl@56480
   757
lemma neg_divide_le_eq [field_simps]: "c < 0 \<Longrightarrow> b / c \<le> a \<longleftrightarrow> a * c \<le> b"
haftmann@36301
   758
proof -
haftmann@36301
   759
  assume less: "c<0"
haftmann@36301
   760
  hence "(b/c \<le> a) = (a*c \<le> (b/c)*c)"
haftmann@36304
   761
    by (simp add: mult_le_cancel_right less_not_sym [OF less] del: times_divide_eq)
haftmann@36301
   762
  also have "... = (a*c \<le> b)"
haftmann@57512
   763
    by (simp add: less_imp_not_eq [OF less] divide_inverse mult.assoc) 
haftmann@36301
   764
  finally show ?thesis .
haftmann@36301
   765
qed
haftmann@36301
   766
hoelzl@56480
   767
text{* The following @{text field_simps} rules are necessary, as minus is always moved atop of
hoelzl@56480
   768
division but we want to get rid of division. *}
hoelzl@56480
   769
hoelzl@56480
   770
lemma pos_le_minus_divide_eq [field_simps]: "0 < c \<Longrightarrow> a \<le> - (b / c) \<longleftrightarrow> a * c \<le> - b"
hoelzl@56480
   771
  unfolding minus_divide_left by (rule pos_le_divide_eq)
hoelzl@56480
   772
hoelzl@56480
   773
lemma neg_le_minus_divide_eq [field_simps]: "c < 0 \<Longrightarrow> a \<le> - (b / c) \<longleftrightarrow> - b \<le> a * c"
hoelzl@56480
   774
  unfolding minus_divide_left by (rule neg_le_divide_eq)
hoelzl@56480
   775
hoelzl@56480
   776
lemma pos_less_minus_divide_eq [field_simps]: "0 < c \<Longrightarrow> a < - (b / c) \<longleftrightarrow> a * c < - b"
hoelzl@56480
   777
  unfolding minus_divide_left by (rule pos_less_divide_eq)
hoelzl@56480
   778
hoelzl@56480
   779
lemma neg_less_minus_divide_eq [field_simps]: "c < 0 \<Longrightarrow> a < - (b / c) \<longleftrightarrow> - b < a * c"
hoelzl@56480
   780
  unfolding minus_divide_left by (rule neg_less_divide_eq)
hoelzl@56480
   781
hoelzl@56480
   782
lemma pos_minus_divide_less_eq [field_simps]: "0 < c \<Longrightarrow> - (b / c) < a \<longleftrightarrow> - b < a * c"
hoelzl@56480
   783
  unfolding minus_divide_left by (rule pos_divide_less_eq)
hoelzl@56480
   784
hoelzl@56480
   785
lemma neg_minus_divide_less_eq [field_simps]: "c < 0 \<Longrightarrow> - (b / c) < a \<longleftrightarrow> a * c < - b"
hoelzl@56480
   786
  unfolding minus_divide_left by (rule neg_divide_less_eq)
hoelzl@56480
   787
hoelzl@56480
   788
lemma pos_minus_divide_le_eq [field_simps]: "0 < c \<Longrightarrow> - (b / c) \<le> a \<longleftrightarrow> - b \<le> a * c"
hoelzl@56480
   789
  unfolding minus_divide_left by (rule pos_divide_le_eq)
hoelzl@56480
   790
hoelzl@56480
   791
lemma neg_minus_divide_le_eq [field_simps]: "c < 0 \<Longrightarrow> - (b / c) \<le> a \<longleftrightarrow> a * c \<le> - b"
hoelzl@56480
   792
  unfolding minus_divide_left by (rule neg_divide_le_eq)
hoelzl@56480
   793
lp15@56365
   794
lemma frac_less_eq:
lp15@56365
   795
  "y \<noteq> 0 \<Longrightarrow> z \<noteq> 0 \<Longrightarrow> x / y < w / z \<longleftrightarrow> (x * z - w * y) / (y * z) < 0"
lp15@56365
   796
  by (subst less_iff_diff_less_0) (simp add: diff_frac_eq )
lp15@56365
   797
lp15@56365
   798
lemma frac_le_eq:
lp15@56365
   799
  "y \<noteq> 0 \<Longrightarrow> z \<noteq> 0 \<Longrightarrow> x / y \<le> w / z \<longleftrightarrow> (x * z - w * y) / (y * z) \<le> 0"
lp15@56365
   800
  by (subst le_iff_diff_le_0) (simp add: diff_frac_eq )
lp15@56365
   801
haftmann@36301
   802
text{* Lemmas @{text sign_simps} is a first attempt to automate proofs
haftmann@36301
   803
of positivity/negativity needed for @{text field_simps}. Have not added @{text
haftmann@36301
   804
sign_simps} to @{text field_simps} because the former can lead to case
haftmann@36301
   805
explosions. *}
haftmann@36301
   806
blanchet@54147
   807
lemmas sign_simps = algebra_simps zero_less_mult_iff mult_less_0_iff
haftmann@36348
   808
blanchet@54147
   809
lemmas (in -) sign_simps = algebra_simps zero_less_mult_iff mult_less_0_iff
haftmann@36301
   810
haftmann@36301
   811
(* Only works once linear arithmetic is installed:
haftmann@36301
   812
text{*An example:*}
haftmann@36301
   813
lemma fixes a b c d e f :: "'a::linordered_field"
haftmann@36301
   814
shows "\<lbrakk>a>b; c<d; e<f; 0 < u \<rbrakk> \<Longrightarrow>
haftmann@36301
   815
 ((a-b)*(c-d)*(e-f))/((c-d)*(e-f)*(a-b)) <
haftmann@36301
   816
 ((e-f)*(a-b)*(c-d))/((e-f)*(a-b)*(c-d)) + u"
haftmann@36301
   817
apply(subgoal_tac "(c-d)*(e-f)*(a-b) > 0")
haftmann@36301
   818
 prefer 2 apply(simp add:sign_simps)
haftmann@36301
   819
apply(subgoal_tac "(c-d)*(e-f)*(a-b)*u > 0")
haftmann@36301
   820
 prefer 2 apply(simp add:sign_simps)
haftmann@36301
   821
apply(simp add:field_simps)
haftmann@36301
   822
done
haftmann@36301
   823
*)
haftmann@36301
   824
nipkow@56541
   825
lemma divide_pos_pos[simp]:
haftmann@36301
   826
  "0 < x ==> 0 < y ==> 0 < x / y"
haftmann@36301
   827
by(simp add:field_simps)
haftmann@36301
   828
haftmann@36301
   829
lemma divide_nonneg_pos:
haftmann@36301
   830
  "0 <= x ==> 0 < y ==> 0 <= x / y"
haftmann@36301
   831
by(simp add:field_simps)
haftmann@36301
   832
haftmann@36301
   833
lemma divide_neg_pos:
haftmann@36301
   834
  "x < 0 ==> 0 < y ==> x / y < 0"
haftmann@36301
   835
by(simp add:field_simps)
haftmann@36301
   836
haftmann@36301
   837
lemma divide_nonpos_pos:
haftmann@36301
   838
  "x <= 0 ==> 0 < y ==> x / y <= 0"
haftmann@36301
   839
by(simp add:field_simps)
haftmann@36301
   840
haftmann@36301
   841
lemma divide_pos_neg:
haftmann@36301
   842
  "0 < x ==> y < 0 ==> x / y < 0"
haftmann@36301
   843
by(simp add:field_simps)
haftmann@36301
   844
haftmann@36301
   845
lemma divide_nonneg_neg:
haftmann@36301
   846
  "0 <= x ==> y < 0 ==> x / y <= 0" 
haftmann@36301
   847
by(simp add:field_simps)
haftmann@36301
   848
haftmann@36301
   849
lemma divide_neg_neg:
haftmann@36301
   850
  "x < 0 ==> y < 0 ==> 0 < x / y"
haftmann@36301
   851
by(simp add:field_simps)
haftmann@36301
   852
haftmann@36301
   853
lemma divide_nonpos_neg:
haftmann@36301
   854
  "x <= 0 ==> y < 0 ==> 0 <= x / y"
haftmann@36301
   855
by(simp add:field_simps)
haftmann@36301
   856
haftmann@36301
   857
lemma divide_strict_right_mono:
haftmann@36301
   858
     "[|a < b; 0 < c|] ==> a / c < b / c"
haftmann@36301
   859
by (simp add: less_imp_not_eq2 divide_inverse mult_strict_right_mono 
haftmann@36301
   860
              positive_imp_inverse_positive)
haftmann@36301
   861
haftmann@36301
   862
haftmann@36301
   863
lemma divide_strict_right_mono_neg:
haftmann@36301
   864
     "[|b < a; c < 0|] ==> a / c < b / c"
haftmann@36301
   865
apply (drule divide_strict_right_mono [of _ _ "-c"], simp)
haftmann@36301
   866
apply (simp add: less_imp_not_eq nonzero_minus_divide_right [symmetric])
haftmann@36301
   867
done
haftmann@36301
   868
haftmann@36301
   869
text{*The last premise ensures that @{term a} and @{term b} 
haftmann@36301
   870
      have the same sign*}
haftmann@36301
   871
lemma divide_strict_left_mono:
haftmann@36301
   872
  "[|b < a; 0 < c; 0 < a*b|] ==> c / a < c / b"
huffman@44921
   873
  by (auto simp: field_simps zero_less_mult_iff mult_strict_right_mono)
haftmann@36301
   874
haftmann@36301
   875
lemma divide_left_mono:
haftmann@36301
   876
  "[|b \<le> a; 0 \<le> c; 0 < a*b|] ==> c / a \<le> c / b"
huffman@44921
   877
  by (auto simp: field_simps zero_less_mult_iff mult_right_mono)
haftmann@36301
   878
haftmann@36301
   879
lemma divide_strict_left_mono_neg:
haftmann@36301
   880
  "[|a < b; c < 0; 0 < a*b|] ==> c / a < c / b"
huffman@44921
   881
  by (auto simp: field_simps zero_less_mult_iff mult_strict_right_mono_neg)
haftmann@36301
   882
haftmann@36301
   883
lemma mult_imp_div_pos_le: "0 < y ==> x <= z * y ==>
haftmann@36301
   884
    x / y <= z"
haftmann@36301
   885
by (subst pos_divide_le_eq, assumption+)
haftmann@36301
   886
haftmann@36301
   887
lemma mult_imp_le_div_pos: "0 < y ==> z * y <= x ==>
haftmann@36301
   888
    z <= x / y"
haftmann@36301
   889
by(simp add:field_simps)
haftmann@36301
   890
haftmann@36301
   891
lemma mult_imp_div_pos_less: "0 < y ==> x < z * y ==>
haftmann@36301
   892
    x / y < z"
haftmann@36301
   893
by(simp add:field_simps)
haftmann@36301
   894
haftmann@36301
   895
lemma mult_imp_less_div_pos: "0 < y ==> z * y < x ==>
haftmann@36301
   896
    z < x / y"
haftmann@36301
   897
by(simp add:field_simps)
haftmann@36301
   898
haftmann@36301
   899
lemma frac_le: "0 <= x ==> 
haftmann@36301
   900
    x <= y ==> 0 < w ==> w <= z  ==> x / z <= y / w"
haftmann@36301
   901
  apply (rule mult_imp_div_pos_le)
haftmann@36301
   902
  apply simp
haftmann@36301
   903
  apply (subst times_divide_eq_left)
haftmann@36301
   904
  apply (rule mult_imp_le_div_pos, assumption)
haftmann@36301
   905
  apply (rule mult_mono)
haftmann@36301
   906
  apply simp_all
haftmann@36301
   907
done
haftmann@36301
   908
haftmann@36301
   909
lemma frac_less: "0 <= x ==> 
haftmann@36301
   910
    x < y ==> 0 < w ==> w <= z  ==> x / z < y / w"
haftmann@36301
   911
  apply (rule mult_imp_div_pos_less)
haftmann@36301
   912
  apply simp
haftmann@36301
   913
  apply (subst times_divide_eq_left)
haftmann@36301
   914
  apply (rule mult_imp_less_div_pos, assumption)
haftmann@36301
   915
  apply (erule mult_less_le_imp_less)
haftmann@36301
   916
  apply simp_all
haftmann@36301
   917
done
haftmann@36301
   918
haftmann@36301
   919
lemma frac_less2: "0 < x ==> 
haftmann@36301
   920
    x <= y ==> 0 < w ==> w < z  ==> x / z < y / w"
haftmann@36301
   921
  apply (rule mult_imp_div_pos_less)
haftmann@36301
   922
  apply simp_all
haftmann@36301
   923
  apply (rule mult_imp_less_div_pos, assumption)
haftmann@36301
   924
  apply (erule mult_le_less_imp_less)
haftmann@36301
   925
  apply simp_all
haftmann@36301
   926
done
haftmann@36301
   927
haftmann@36301
   928
lemma less_half_sum: "a < b ==> a < (a+b) / (1+1)"
haftmann@36301
   929
by (simp add: field_simps zero_less_two)
haftmann@36301
   930
haftmann@36301
   931
lemma gt_half_sum: "a < b ==> (a+b)/(1+1) < b"
haftmann@36301
   932
by (simp add: field_simps zero_less_two)
haftmann@36301
   933
hoelzl@53215
   934
subclass unbounded_dense_linorder
haftmann@36301
   935
proof
haftmann@36301
   936
  fix x y :: 'a
haftmann@36301
   937
  from less_add_one show "\<exists>y. x < y" .. 
haftmann@36301
   938
  from less_add_one have "x + (- 1) < (x + 1) + (- 1)" by (rule add_strict_right_mono)
haftmann@54230
   939
  then have "x - 1 < x + 1 - 1" by simp
haftmann@36301
   940
  then have "x - 1 < x" by (simp add: algebra_simps)
haftmann@36301
   941
  then show "\<exists>y. y < x" ..
haftmann@36301
   942
  show "x < y \<Longrightarrow> \<exists>z>x. z < y" by (blast intro!: less_half_sum gt_half_sum)
haftmann@36301
   943
qed
haftmann@36301
   944
haftmann@36301
   945
lemma nonzero_abs_inverse:
haftmann@36301
   946
     "a \<noteq> 0 ==> \<bar>inverse a\<bar> = inverse \<bar>a\<bar>"
haftmann@36301
   947
apply (auto simp add: neq_iff abs_if nonzero_inverse_minus_eq 
haftmann@36301
   948
                      negative_imp_inverse_negative)
haftmann@36301
   949
apply (blast intro: positive_imp_inverse_positive elim: less_asym) 
haftmann@36301
   950
done
haftmann@36301
   951
haftmann@36301
   952
lemma nonzero_abs_divide:
haftmann@36301
   953
     "b \<noteq> 0 ==> \<bar>a / b\<bar> = \<bar>a\<bar> / \<bar>b\<bar>"
haftmann@36301
   954
  by (simp add: divide_inverse abs_mult nonzero_abs_inverse) 
haftmann@36301
   955
haftmann@36301
   956
lemma field_le_epsilon:
haftmann@36301
   957
  assumes e: "\<And>e. 0 < e \<Longrightarrow> x \<le> y + e"
haftmann@36301
   958
  shows "x \<le> y"
haftmann@36301
   959
proof (rule dense_le)
haftmann@36301
   960
  fix t assume "t < x"
haftmann@36301
   961
  hence "0 < x - t" by (simp add: less_diff_eq)
haftmann@36301
   962
  from e [OF this] have "x + 0 \<le> x + (y - t)" by (simp add: algebra_simps)
haftmann@36301
   963
  then have "0 \<le> y - t" by (simp only: add_le_cancel_left)
haftmann@36301
   964
  then show "t \<le> y" by (simp add: algebra_simps)
haftmann@36301
   965
qed
haftmann@36301
   966
haftmann@36301
   967
end
haftmann@36301
   968
haftmann@36414
   969
class linordered_field_inverse_zero = linordered_field + field_inverse_zero
haftmann@36348
   970
begin
haftmann@36348
   971
paulson@14277
   972
lemma inverse_positive_iff_positive [simp]:
haftmann@36409
   973
  "(0 < inverse a) = (0 < a)"
haftmann@21328
   974
apply (cases "a = 0", simp)
paulson@14277
   975
apply (blast intro: inverse_positive_imp_positive positive_imp_inverse_positive)
paulson@14277
   976
done
paulson@14277
   977
paulson@14277
   978
lemma inverse_negative_iff_negative [simp]:
haftmann@36409
   979
  "(inverse a < 0) = (a < 0)"
haftmann@21328
   980
apply (cases "a = 0", simp)
paulson@14277
   981
apply (blast intro: inverse_negative_imp_negative negative_imp_inverse_negative)
paulson@14277
   982
done
paulson@14277
   983
paulson@14277
   984
lemma inverse_nonnegative_iff_nonnegative [simp]:
haftmann@36409
   985
  "0 \<le> inverse a \<longleftrightarrow> 0 \<le> a"
haftmann@36409
   986
  by (simp add: not_less [symmetric])
paulson@14277
   987
paulson@14277
   988
lemma inverse_nonpositive_iff_nonpositive [simp]:
haftmann@36409
   989
  "inverse a \<le> 0 \<longleftrightarrow> a \<le> 0"
haftmann@36409
   990
  by (simp add: not_less [symmetric])
paulson@14277
   991
hoelzl@56480
   992
lemma one_less_inverse_iff: "1 < inverse x \<longleftrightarrow> 0 < x \<and> x < 1"
hoelzl@56480
   993
  using less_trans[of 1 x 0 for x]
hoelzl@56480
   994
  by (cases x 0 rule: linorder_cases) (auto simp add: field_simps)
paulson@14365
   995
hoelzl@56480
   996
lemma one_le_inverse_iff: "1 \<le> inverse x \<longleftrightarrow> 0 < x \<and> x \<le> 1"
haftmann@36409
   997
proof (cases "x = 1")
haftmann@36409
   998
  case True then show ?thesis by simp
haftmann@36409
   999
next
haftmann@36409
  1000
  case False then have "inverse x \<noteq> 1" by simp
haftmann@36409
  1001
  then have "1 \<noteq> inverse x" by blast
haftmann@36409
  1002
  then have "1 \<le> inverse x \<longleftrightarrow> 1 < inverse x" by (simp add: le_less)
haftmann@36409
  1003
  with False show ?thesis by (auto simp add: one_less_inverse_iff)
haftmann@36409
  1004
qed
paulson@14365
  1005
hoelzl@56480
  1006
lemma inverse_less_1_iff: "inverse x < 1 \<longleftrightarrow> x \<le> 0 \<or> 1 < x"
haftmann@36409
  1007
  by (simp add: not_le [symmetric] one_le_inverse_iff) 
paulson@14365
  1008
hoelzl@56480
  1009
lemma inverse_le_1_iff: "inverse x \<le> 1 \<longleftrightarrow> x \<le> 0 \<or> 1 \<le> x"
haftmann@36409
  1010
  by (simp add: not_less [symmetric] one_less_inverse_iff) 
paulson@14365
  1011
hoelzl@56481
  1012
lemma [divide_simps]:
hoelzl@56480
  1013
  shows le_divide_eq: "a \<le> b / c \<longleftrightarrow> (if 0 < c then a * c \<le> b else if c < 0 then b \<le> a * c else a \<le> 0)"
hoelzl@56480
  1014
    and divide_le_eq: "b / c \<le> a \<longleftrightarrow> (if 0 < c then b \<le> a * c else if c < 0 then a * c \<le> b else 0 \<le> a)"
hoelzl@56480
  1015
    and less_divide_eq: "a < b / c \<longleftrightarrow> (if 0 < c then a * c < b else if c < 0 then b < a * c else a < 0)"
hoelzl@56480
  1016
    and divide_less_eq: "b / c < a \<longleftrightarrow> (if 0 < c then b < a * c else if c < 0 then a * c < b else 0 < a)"
hoelzl@56481
  1017
    and le_minus_divide_eq: "a \<le> - (b / c) \<longleftrightarrow> (if 0 < c then a * c \<le> - b else if c < 0 then - b \<le> a * c else a \<le> 0)"
hoelzl@56481
  1018
    and minus_divide_le_eq: "- (b / c) \<le> a \<longleftrightarrow> (if 0 < c then - b \<le> a * c else if c < 0 then a * c \<le> - b else 0 \<le> a)"
hoelzl@56481
  1019
    and less_minus_divide_eq: "a < - (b / c) \<longleftrightarrow> (if 0 < c then a * c < - b else if c < 0 then - b < a * c else  a < 0)"
hoelzl@56481
  1020
    and minus_divide_less_eq: "- (b / c) < a \<longleftrightarrow> (if 0 < c then - b < a * c else if c < 0 then a * c < - b else 0 < a)"
hoelzl@56480
  1021
  by (auto simp: field_simps not_less dest: antisym)
paulson@14288
  1022
haftmann@36301
  1023
text {*Division and Signs*}
avigad@16775
  1024
hoelzl@56480
  1025
lemma
hoelzl@56480
  1026
  shows zero_less_divide_iff: "0 < a / b \<longleftrightarrow> 0 < a \<and> 0 < b \<or> a < 0 \<and> b < 0"
hoelzl@56480
  1027
    and divide_less_0_iff: "a / b < 0 \<longleftrightarrow> 0 < a \<and> b < 0 \<or> a < 0 \<and> 0 < b"
hoelzl@56480
  1028
    and zero_le_divide_iff: "0 \<le> a / b \<longleftrightarrow> 0 \<le> a \<and> 0 \<le> b \<or> a \<le> 0 \<and> b \<le> 0"
hoelzl@56480
  1029
    and divide_le_0_iff: "a / b \<le> 0 \<longleftrightarrow> 0 \<le> a \<and> b \<le> 0 \<or> a \<le> 0 \<and> 0 \<le> b"
hoelzl@56481
  1030
  by (auto simp add: divide_simps)
avigad@16775
  1031
haftmann@36301
  1032
text {* Division and the Number One *}
paulson@14353
  1033
paulson@14353
  1034
text{*Simplify expressions equated with 1*}
paulson@14353
  1035
hoelzl@56480
  1036
lemma zero_eq_1_divide_iff [simp]: "0 = 1 / a \<longleftrightarrow> a = 0"
hoelzl@56480
  1037
  by (cases "a = 0") (auto simp: field_simps)
paulson@14353
  1038
hoelzl@56480
  1039
lemma one_divide_eq_0_iff [simp]: "1 / a = 0 \<longleftrightarrow> a = 0"
hoelzl@56480
  1040
  using zero_eq_1_divide_iff[of a] by simp
paulson@14353
  1041
paulson@14353
  1042
text{*Simplify expressions such as @{text "0 < 1/x"} to @{text "0 < x"}*}
haftmann@36423
  1043
blanchet@54147
  1044
lemma zero_le_divide_1_iff [simp]:
haftmann@36423
  1045
  "0 \<le> 1 / a \<longleftrightarrow> 0 \<le> a"
haftmann@36423
  1046
  by (simp add: zero_le_divide_iff)
paulson@17085
  1047
blanchet@54147
  1048
lemma zero_less_divide_1_iff [simp]:
haftmann@36423
  1049
  "0 < 1 / a \<longleftrightarrow> 0 < a"
haftmann@36423
  1050
  by (simp add: zero_less_divide_iff)
haftmann@36423
  1051
blanchet@54147
  1052
lemma divide_le_0_1_iff [simp]:
haftmann@36423
  1053
  "1 / a \<le> 0 \<longleftrightarrow> a \<le> 0"
haftmann@36423
  1054
  by (simp add: divide_le_0_iff)
haftmann@36423
  1055
blanchet@54147
  1056
lemma divide_less_0_1_iff [simp]:
haftmann@36423
  1057
  "1 / a < 0 \<longleftrightarrow> a < 0"
haftmann@36423
  1058
  by (simp add: divide_less_0_iff)
paulson@14353
  1059
paulson@14293
  1060
lemma divide_right_mono:
haftmann@36409
  1061
     "[|a \<le> b; 0 \<le> c|] ==> a/c \<le> b/c"
haftmann@36409
  1062
by (force simp add: divide_strict_right_mono le_less)
paulson@14293
  1063
haftmann@36409
  1064
lemma divide_right_mono_neg: "a <= b 
avigad@16775
  1065
    ==> c <= 0 ==> b / c <= a / c"
nipkow@23482
  1066
apply (drule divide_right_mono [of _ _ "- c"])
hoelzl@56479
  1067
apply auto
avigad@16775
  1068
done
avigad@16775
  1069
haftmann@36409
  1070
lemma divide_left_mono_neg: "a <= b 
avigad@16775
  1071
    ==> c <= 0 ==> 0 < a * b ==> c / a <= c / b"
avigad@16775
  1072
  apply (drule divide_left_mono [of _ _ "- c"])
haftmann@57512
  1073
  apply (auto simp add: mult.commute)
avigad@16775
  1074
done
avigad@16775
  1075
hoelzl@56480
  1076
lemma inverse_le_iff: "inverse a \<le> inverse b \<longleftrightarrow> (0 < a * b \<longrightarrow> b \<le> a) \<and> (a * b \<le> 0 \<longrightarrow> a \<le> b)"
hoelzl@56480
  1077
  by (cases a 0 b 0 rule: linorder_cases[case_product linorder_cases])
hoelzl@56480
  1078
     (auto simp add: field_simps zero_less_mult_iff mult_le_0_iff)
hoelzl@42904
  1079
hoelzl@56480
  1080
lemma inverse_less_iff: "inverse a < inverse b \<longleftrightarrow> (0 < a * b \<longrightarrow> b < a) \<and> (a * b \<le> 0 \<longrightarrow> a < b)"
hoelzl@42904
  1081
  by (subst less_le) (auto simp: inverse_le_iff)
hoelzl@42904
  1082
hoelzl@56480
  1083
lemma divide_le_cancel: "a / c \<le> b / c \<longleftrightarrow> (0 < c \<longrightarrow> a \<le> b) \<and> (c < 0 \<longrightarrow> b \<le> a)"
hoelzl@42904
  1084
  by (simp add: divide_inverse mult_le_cancel_right)
hoelzl@42904
  1085
hoelzl@56480
  1086
lemma divide_less_cancel: "a / c < b / c \<longleftrightarrow> (0 < c \<longrightarrow> a < b) \<and> (c < 0 \<longrightarrow> b < a) \<and> c \<noteq> 0"
hoelzl@42904
  1087
  by (auto simp add: divide_inverse mult_less_cancel_right)
hoelzl@42904
  1088
avigad@16775
  1089
text{*Simplify quotients that are compared with the value 1.*}
avigad@16775
  1090
blanchet@54147
  1091
lemma le_divide_eq_1:
haftmann@36409
  1092
  "(1 \<le> b / a) = ((0 < a & a \<le> b) | (a < 0 & b \<le> a))"
avigad@16775
  1093
by (auto simp add: le_divide_eq)
avigad@16775
  1094
blanchet@54147
  1095
lemma divide_le_eq_1:
haftmann@36409
  1096
  "(b / a \<le> 1) = ((0 < a & b \<le> a) | (a < 0 & a \<le> b) | a=0)"
avigad@16775
  1097
by (auto simp add: divide_le_eq)
avigad@16775
  1098
blanchet@54147
  1099
lemma less_divide_eq_1:
haftmann@36409
  1100
  "(1 < b / a) = ((0 < a & a < b) | (a < 0 & b < a))"
avigad@16775
  1101
by (auto simp add: less_divide_eq)
avigad@16775
  1102
blanchet@54147
  1103
lemma divide_less_eq_1:
haftmann@36409
  1104
  "(b / a < 1) = ((0 < a & b < a) | (a < 0 & a < b) | a=0)"
avigad@16775
  1105
by (auto simp add: divide_less_eq)
avigad@16775
  1106
hoelzl@56571
  1107
lemma divide_nonneg_nonneg [simp]:
hoelzl@56571
  1108
  "0 \<le> x \<Longrightarrow> 0 \<le> y \<Longrightarrow> 0 \<le> x / y"
hoelzl@56571
  1109
  by (auto simp add: divide_simps)
hoelzl@56571
  1110
hoelzl@56571
  1111
lemma divide_nonpos_nonpos:
hoelzl@56571
  1112
  "x \<le> 0 \<Longrightarrow> y \<le> 0 \<Longrightarrow> 0 \<le> x / y"
hoelzl@56571
  1113
  by (auto simp add: divide_simps)
hoelzl@56571
  1114
hoelzl@56571
  1115
lemma divide_nonneg_nonpos:
hoelzl@56571
  1116
  "0 \<le> x \<Longrightarrow> y \<le> 0 \<Longrightarrow> x / y \<le> 0"
hoelzl@56571
  1117
  by (auto simp add: divide_simps)
hoelzl@56571
  1118
hoelzl@56571
  1119
lemma divide_nonpos_nonneg:
hoelzl@56571
  1120
  "x \<le> 0 \<Longrightarrow> 0 \<le> y \<Longrightarrow> x / y \<le> 0"
hoelzl@56571
  1121
  by (auto simp add: divide_simps)
wenzelm@23389
  1122
haftmann@36301
  1123
text {*Conditional Simplification Rules: No Case Splits*}
avigad@16775
  1124
blanchet@54147
  1125
lemma le_divide_eq_1_pos [simp]:
haftmann@36409
  1126
  "0 < a \<Longrightarrow> (1 \<le> b/a) = (a \<le> b)"
avigad@16775
  1127
by (auto simp add: le_divide_eq)
avigad@16775
  1128
blanchet@54147
  1129
lemma le_divide_eq_1_neg [simp]:
haftmann@36409
  1130
  "a < 0 \<Longrightarrow> (1 \<le> b/a) = (b \<le> a)"
avigad@16775
  1131
by (auto simp add: le_divide_eq)
avigad@16775
  1132
blanchet@54147
  1133
lemma divide_le_eq_1_pos [simp]:
haftmann@36409
  1134
  "0 < a \<Longrightarrow> (b/a \<le> 1) = (b \<le> a)"
avigad@16775
  1135
by (auto simp add: divide_le_eq)
avigad@16775
  1136
blanchet@54147
  1137
lemma divide_le_eq_1_neg [simp]:
haftmann@36409
  1138
  "a < 0 \<Longrightarrow> (b/a \<le> 1) = (a \<le> b)"
avigad@16775
  1139
by (auto simp add: divide_le_eq)
avigad@16775
  1140
blanchet@54147
  1141
lemma less_divide_eq_1_pos [simp]:
haftmann@36409
  1142
  "0 < a \<Longrightarrow> (1 < b/a) = (a < b)"
avigad@16775
  1143
by (auto simp add: less_divide_eq)
avigad@16775
  1144
blanchet@54147
  1145
lemma less_divide_eq_1_neg [simp]:
haftmann@36409
  1146
  "a < 0 \<Longrightarrow> (1 < b/a) = (b < a)"
avigad@16775
  1147
by (auto simp add: less_divide_eq)
avigad@16775
  1148
blanchet@54147
  1149
lemma divide_less_eq_1_pos [simp]:
haftmann@36409
  1150
  "0 < a \<Longrightarrow> (b/a < 1) = (b < a)"
paulson@18649
  1151
by (auto simp add: divide_less_eq)
paulson@18649
  1152
blanchet@54147
  1153
lemma divide_less_eq_1_neg [simp]:
haftmann@36409
  1154
  "a < 0 \<Longrightarrow> b/a < 1 <-> a < b"
avigad@16775
  1155
by (auto simp add: divide_less_eq)
avigad@16775
  1156
blanchet@54147
  1157
lemma eq_divide_eq_1 [simp]:
haftmann@36409
  1158
  "(1 = b/a) = ((a \<noteq> 0 & a = b))"
avigad@16775
  1159
by (auto simp add: eq_divide_eq)
avigad@16775
  1160
blanchet@54147
  1161
lemma divide_eq_eq_1 [simp]:
haftmann@36409
  1162
  "(b/a = 1) = ((a \<noteq> 0 & a = b))"
avigad@16775
  1163
by (auto simp add: divide_eq_eq)
avigad@16775
  1164
paulson@14294
  1165
lemma abs_inverse [simp]:
haftmann@36409
  1166
     "\<bar>inverse a\<bar> = 
haftmann@36301
  1167
      inverse \<bar>a\<bar>"
haftmann@21328
  1168
apply (cases "a=0", simp) 
paulson@14294
  1169
apply (simp add: nonzero_abs_inverse) 
paulson@14294
  1170
done
paulson@14294
  1171
paulson@15234
  1172
lemma abs_divide [simp]:
haftmann@36409
  1173
     "\<bar>a / b\<bar> = \<bar>a\<bar> / \<bar>b\<bar>"
haftmann@21328
  1174
apply (cases "b=0", simp) 
paulson@14294
  1175
apply (simp add: nonzero_abs_divide) 
paulson@14294
  1176
done
paulson@14294
  1177
haftmann@36409
  1178
lemma abs_div_pos: "0 < y ==> 
haftmann@36301
  1179
    \<bar>x\<bar> / y = \<bar>x / y\<bar>"
haftmann@25304
  1180
  apply (subst abs_divide)
haftmann@25304
  1181
  apply (simp add: order_less_imp_le)
haftmann@25304
  1182
done
avigad@16775
  1183
lp15@55718
  1184
lemma zero_le_divide_abs_iff [simp]: "(0 \<le> a / abs b) = (0 \<le> a | b = 0)" 
lp15@55718
  1185
by (auto simp: zero_le_divide_iff)
lp15@55718
  1186
lp15@55718
  1187
lemma divide_le_0_abs_iff [simp]: "(a / abs b \<le> 0) = (a \<le> 0 | b = 0)" 
lp15@55718
  1188
by (auto simp: divide_le_0_iff)
lp15@55718
  1189
hoelzl@35579
  1190
lemma field_le_mult_one_interval:
hoelzl@35579
  1191
  assumes *: "\<And>z. \<lbrakk> 0 < z ; z < 1 \<rbrakk> \<Longrightarrow> z * x \<le> y"
hoelzl@35579
  1192
  shows "x \<le> y"
hoelzl@35579
  1193
proof (cases "0 < x")
hoelzl@35579
  1194
  assume "0 < x"
hoelzl@35579
  1195
  thus ?thesis
hoelzl@35579
  1196
    using dense_le_bounded[of 0 1 "y/x"] *
hoelzl@35579
  1197
    unfolding le_divide_eq if_P[OF `0 < x`] by simp
hoelzl@35579
  1198
next
hoelzl@35579
  1199
  assume "\<not>0 < x" hence "x \<le> 0" by simp
hoelzl@35579
  1200
  obtain s::'a where s: "0 < s" "s < 1" using dense[of 0 "1\<Colon>'a"] by auto
hoelzl@35579
  1201
  hence "x \<le> s * x" using mult_le_cancel_right[of 1 x s] `x \<le> 0` by auto
hoelzl@35579
  1202
  also note *[OF s]
hoelzl@35579
  1203
  finally show ?thesis .
hoelzl@35579
  1204
qed
haftmann@35090
  1205
haftmann@36409
  1206
end
haftmann@36409
  1207
haftmann@52435
  1208
code_identifier
haftmann@52435
  1209
  code_module Fields \<rightharpoonup> (SML) Arith and (OCaml) Arith and (Haskell) Arith
haftmann@33364
  1210
paulson@14265
  1211
end