src/HOL/OrderedGroup.thy

(temporal deactivation)

(*  Title:   HOL/OrderedGroup.thy
    ID:      $Id$
    Author:  Gertrud Bauer, Steven Obua, Lawrence C Paulson, and Markus Wenzel,
             with contributions by Jeremy Avigad
*)

header {* Ordered Groups *}

theory OrderedGroup
imports Lattices
uses "~~/src/Provers/Arith/abel_cancel.ML"
begin

text {*
  The theory of partially ordered groups is taken from the books:
  \begin{itemize}
  \item \emph{Lattice Theory} by Garret Birkhoff, American Mathematical Society 1979 
  \item \emph{Partially Ordered Algebraic Systems}, Pergamon Press 1963
  \end{itemize}
  Most of the used notions can also be looked up in 
  \begin{itemize}
  \item \url{http://www.mathworld.com} by Eric Weisstein et. al.
  \item \emph{Algebra I} by van der Waerden, Springer.
  \end{itemize}
*}

subsection {* Semigroups and Monoids *}

class semigroup_add = plus +
  assumes add_assoc: "(a + b) + c = a + (b + c)"

class ab_semigroup_add = semigroup_add +
  assumes add_commute: "a + b = b + a"
begin

lemma add_left_commute: "a + (b + c) = b + (a + c)"
  by (rule mk_left_commute [of "plus", OF add_assoc add_commute])

theorems add_ac = add_assoc add_commute add_left_commute

end

theorems add_ac = add_assoc add_commute add_left_commute

class semigroup_mult = times +
  assumes mult_assoc: "(a * b) * c = a * (b * c)"

class ab_semigroup_mult = semigroup_mult +
  assumes mult_commute: "a * b = b * a"
begin

lemma mult_left_commute: "a * (b * c) = b * (a * c)"
  by (rule mk_left_commute [of "times", OF mult_assoc mult_commute])

theorems mult_ac = mult_assoc mult_commute mult_left_commute

end

theorems mult_ac = mult_assoc mult_commute mult_left_commute

class ab_semigroup_idem_mult = ab_semigroup_mult +
  assumes mult_idem: "x * x = x"
begin

lemma mult_left_idem: "x * (x * y) = x * y"
  unfolding mult_assoc [symmetric, of x] mult_idem ..

lemmas mult_ac_idem = mult_ac mult_idem mult_left_idem

end

lemmas mult_ac_idem = mult_ac mult_idem mult_left_idem

class monoid_add = zero + semigroup_add +
  assumes add_0_left [simp]: "0 + a = a"
    and add_0_right [simp]: "a + 0 = a"

lemma zero_reorient: "0 = x \<longleftrightarrow> x = 0"
  by (rule eq_commute)

class comm_monoid_add = zero + ab_semigroup_add +
  assumes add_0: "0 + a = a"
begin

subclass monoid_add
  by unfold_locales (insert add_0, simp_all add: add_commute)

end

class monoid_mult = one + semigroup_mult +
  assumes mult_1_left [simp]: "1 * a  = a"
  assumes mult_1_right [simp]: "a * 1 = a"

lemma one_reorient: "1 = x \<longleftrightarrow> x = 1"
  by (rule eq_commute)

class comm_monoid_mult = one + ab_semigroup_mult +
  assumes mult_1: "1 * a = a"
begin

subclass monoid_mult
  by unfold_locales (insert mult_1, simp_all add: mult_commute)

end

class cancel_semigroup_add = semigroup_add +
  assumes add_left_imp_eq: "a + b = a + c \<Longrightarrow> b = c"
  assumes add_right_imp_eq: "b + a = c + a \<Longrightarrow> b = c"
begin

lemma add_left_cancel [simp]:
  "a + b = a + c \<longleftrightarrow> b = c"
  by (blast dest: add_left_imp_eq)

lemma add_right_cancel [simp]:
  "b + a = c + a \<longleftrightarrow> b = c"
  by (blast dest: add_right_imp_eq)

end

class cancel_ab_semigroup_add = ab_semigroup_add +
  assumes add_imp_eq: "a + b = a + c \<Longrightarrow> b = c"
begin

subclass cancel_semigroup_add
proof unfold_locales
  fix a b c :: 'a
  assume "a + b = a + c" 
  then show "b = c" by (rule add_imp_eq)
next
  fix a b c :: 'a
  assume "b + a = c + a"
  then have "a + b = a + c" by (simp only: add_commute)
  then show "b = c" by (rule add_imp_eq)
qed

end

subsection {* Groups *}

class group_add = minus + uminus + monoid_add +
  assumes left_minus [simp]: "- a + a = 0"
  assumes diff_minus: "a - b = a + (- b)"
begin

lemma minus_add_cancel: "- a + (a + b) = b"
  by (simp add: add_assoc[symmetric])

lemma minus_zero [simp]: "- 0 = 0"
proof -
  have "- 0 = - 0 + (0 + 0)" by (simp only: add_0_right)
  also have "\<dots> = 0" by (rule minus_add_cancel)
  finally show ?thesis .
qed

lemma minus_minus [simp]: "- (- a) = a"
proof -
  have "- (- a) = - (- a) + (- a + a)" by simp
  also have "\<dots> = a" by (rule minus_add_cancel)
  finally show ?thesis .
qed

lemma right_minus [simp]: "a + - a = 0"
proof -
  have "a + - a = - (- a) + - a" by simp
  also have "\<dots> = 0" by (rule left_minus)
  finally show ?thesis .
qed

lemma right_minus_eq: "a - b = 0 \<longleftrightarrow> a = b"
proof
  assume "a - b = 0"
  have "a = (a - b) + b" by (simp add:diff_minus add_assoc)
  also have "\<dots> = b" using `a - b = 0` by simp
  finally show "a = b" .
next
  assume "a = b" thus "a - b = 0" by (simp add: diff_minus)
qed

lemma equals_zero_I:
  assumes "a + b = 0"
  shows "- a = b"
proof -
  have "- a = - a + (a + b)" using assms by simp
  also have "\<dots> = b" by (simp add: add_assoc[symmetric])
  finally show ?thesis .
qed

lemma diff_self [simp]: "a - a = 0"
  by (simp add: diff_minus)

lemma diff_0 [simp]: "0 - a = - a"
  by (simp add: diff_minus)

lemma diff_0_right [simp]: "a - 0 = a" 
  by (simp add: diff_minus)

lemma diff_minus_eq_add [simp]: "a - - b = a + b"
  by (simp add: diff_minus)

lemma neg_equal_iff_equal [simp]:
  "- a = - b \<longleftrightarrow> a = b" 
proof 
  assume "- a = - b"
  hence "- (- a) = - (- b)"
    by simp
  thus "a = b" by simp
next
  assume "a = b"
  thus "- a = - b" by simp
qed

lemma neg_equal_0_iff_equal [simp]:
  "- a = 0 \<longleftrightarrow> a = 0"
  by (subst neg_equal_iff_equal [symmetric], simp)

lemma neg_0_equal_iff_equal [simp]:
  "0 = - a \<longleftrightarrow> 0 = a"
  by (subst neg_equal_iff_equal [symmetric], simp)

text{*The next two equations can make the simplifier loop!*}

lemma equation_minus_iff:
  "a = - b \<longleftrightarrow> b = - a"
proof -
  have "- (- a) = - b \<longleftrightarrow> - a = b" by (rule neg_equal_iff_equal)
  thus ?thesis by (simp add: eq_commute)
qed

lemma minus_equation_iff:
  "- a = b \<longleftrightarrow> - b = a"
proof -
  have "- a = - (- b) \<longleftrightarrow> a = -b" by (rule neg_equal_iff_equal)
  thus ?thesis by (simp add: eq_commute)
qed

lemma diff_add_cancel: "a - b + b = a"
  by (simp add: diff_minus add_assoc)

lemma add_diff_cancel: "a + b - b = a"
  by (simp add: diff_minus add_assoc)

end

class ab_group_add = minus + uminus + comm_monoid_add +
  assumes ab_left_minus: "- a + a = 0"
  assumes ab_diff_minus: "a - b = a + (- b)"
begin

subclass group_add
  by unfold_locales (simp_all add: ab_left_minus ab_diff_minus)

subclass cancel_ab_semigroup_add
proof unfold_locales
  fix a b c :: 'a
  assume "a + b = a + c"
  then have "- a + a + b = - a + a + c"
    unfolding add_assoc by simp
  then show "b = c" by simp
qed

lemma uminus_add_conv_diff:
  "- a + b = b - a"
  by (simp add:diff_minus add_commute)

lemma minus_add_distrib [simp]:
  "- (a + b) = - a + - b"
  by (rule equals_zero_I) (simp add: add_ac)

lemma minus_diff_eq [simp]:
  "- (a - b) = b - a"
  by (simp add: diff_minus add_commute)

lemma add_diff_eq: "a + (b - c) = (a + b) - c"
  by (simp add: diff_minus add_ac)

lemma diff_add_eq: "(a - b) + c = (a + c) - b"
  by (simp add: diff_minus add_ac)

lemma diff_eq_eq: "a - b = c \<longleftrightarrow> a = c + b"
  by (auto simp add: diff_minus add_assoc)

lemma eq_diff_eq: "a = c - b \<longleftrightarrow> a + b = c"
  by (auto simp add: diff_minus add_assoc)

lemma diff_diff_eq: "(a - b) - c = a - (b + c)"
  by (simp add: diff_minus add_ac)

lemma diff_diff_eq2: "a - (b - c) = (a + c) - b"
  by (simp add: diff_minus add_ac)

lemmas compare_rls =
       diff_minus [symmetric]
       add_diff_eq diff_add_eq diff_diff_eq diff_diff_eq2
       diff_eq_eq eq_diff_eq

lemma eq_iff_diff_eq_0: "a = b \<longleftrightarrow> a - b = 0"
  by (simp add: compare_rls)

end

subsection {* (Partially) Ordered Groups *} 

class pordered_ab_semigroup_add = order + ab_semigroup_add +
  assumes add_left_mono: "a \<le> b \<Longrightarrow> c + a \<le> c + b"
begin

lemma add_right_mono:
  "a \<le> b \<Longrightarrow> a + c \<le> b + c"
  by (simp add: add_commute [of _ c] add_left_mono)

text {* non-strict, in both arguments *}
lemma add_mono:
  "a \<le> b \<Longrightarrow> c \<le> d \<Longrightarrow> a + c \<le> b + d"
  apply (erule add_right_mono [THEN order_trans])
  apply (simp add: add_commute add_left_mono)
  done

end

class pordered_cancel_ab_semigroup_add =
  pordered_ab_semigroup_add + cancel_ab_semigroup_add
begin

lemma add_strict_left_mono:
  "a < b \<Longrightarrow> c + a < c + b"
  by (auto simp add: less_le add_left_mono)

lemma add_strict_right_mono:
  "a < b \<Longrightarrow> a + c < b + c"
  by (simp add: add_commute [of _ c] add_strict_left_mono)

text{*Strict monotonicity in both arguments*}
lemma add_strict_mono:
  "a < b \<Longrightarrow> c < d \<Longrightarrow> a + c < b + d"
apply (erule add_strict_right_mono [THEN less_trans])
apply (erule add_strict_left_mono)
done

lemma add_less_le_mono:
  "a < b \<Longrightarrow> c \<le> d \<Longrightarrow> a + c < b + d"
apply (erule add_strict_right_mono [THEN less_le_trans])
apply (erule add_left_mono)
done

lemma add_le_less_mono:
  "a \<le> b \<Longrightarrow> c < d \<Longrightarrow> a + c < b + d"
apply (erule add_right_mono [THEN le_less_trans])
apply (erule add_strict_left_mono) 
done

end

class pordered_ab_semigroup_add_imp_le =
  pordered_cancel_ab_semigroup_add +
  assumes add_le_imp_le_left: "c + a \<le> c + b \<Longrightarrow> a \<le> b"
begin

lemma add_less_imp_less_left:
   assumes less: "c + a < c + b"
   shows "a < b"
proof -
  from less have le: "c + a <= c + b" by (simp add: order_le_less)
  have "a <= b" 
    apply (insert le)
    apply (drule add_le_imp_le_left)
    by (insert le, drule add_le_imp_le_left, assumption)
  moreover have "a \<noteq> b"
  proof (rule ccontr)
    assume "~(a \<noteq> b)"
    then have "a = b" by simp
    then have "c + a = c + b" by simp
    with less show "False"by simp
  qed
  ultimately show "a < b" by (simp add: order_le_less)
qed

lemma add_less_imp_less_right:
  "a + c < b + c \<Longrightarrow> a < b"
apply (rule add_less_imp_less_left [of c])
apply (simp add: add_commute)  
done

lemma add_less_cancel_left [simp]:
  "c + a < c + b \<longleftrightarrow> a < b"
  by (blast intro: add_less_imp_less_left add_strict_left_mono) 

lemma add_less_cancel_right [simp]:
  "a + c < b + c \<longleftrightarrow> a < b"
  by (blast intro: add_less_imp_less_right add_strict_right_mono)

lemma add_le_cancel_left [simp]:
  "c + a \<le> c + b \<longleftrightarrow> a \<le> b"
  by (auto, drule add_le_imp_le_left, simp_all add: add_left_mono) 

lemma add_le_cancel_right [simp]:
  "a + c \<le> b + c \<longleftrightarrow> a \<le> b"
  by (simp add: add_commute [of a c] add_commute [of b c])

lemma add_le_imp_le_right:
  "a + c \<le> b + c \<Longrightarrow> a \<le> b"
  by simp

lemma max_add_distrib_left:
  "max x y + z = max (x + z) (y + z)"
  unfolding max_def by auto

lemma min_add_distrib_left:
  "min x y + z = min (x + z) (y + z)"
  unfolding min_def by auto

end

subsection {* Support for reasoning about signs *}

class pordered_comm_monoid_add =
  pordered_cancel_ab_semigroup_add + comm_monoid_add
begin

lemma add_pos_nonneg:
  assumes "0 < a" and "0 \<le> b"
    shows "0 < a + b"
proof -
  have "0 + 0 < a + b" 
    using assms by (rule add_less_le_mono)
  then show ?thesis by simp
qed

lemma add_pos_pos:
  assumes "0 < a" and "0 < b"
    shows "0 < a + b"
  by (rule add_pos_nonneg) (insert assms, auto)

lemma add_nonneg_pos:
  assumes "0 \<le> a" and "0 < b"
    shows "0 < a + b"
proof -
  have "0 + 0 < a + b" 
    using assms by (rule add_le_less_mono)
  then show ?thesis by simp
qed

lemma add_nonneg_nonneg:
  assumes "0 \<le> a" and "0 \<le> b"
    shows "0 \<le> a + b"
proof -
  have "0 + 0 \<le> a + b" 
    using assms by (rule add_mono)
  then show ?thesis by simp
qed

lemma add_neg_nonpos: 
  assumes "a < 0" and "b \<le> 0"
  shows "a + b < 0"
proof -
  have "a + b < 0 + 0"
    using assms by (rule add_less_le_mono)
  then show ?thesis by simp
qed

lemma add_neg_neg: 
  assumes "a < 0" and "b < 0"
  shows "a + b < 0"
  by (rule add_neg_nonpos) (insert assms, auto)

lemma add_nonpos_neg:
  assumes "a \<le> 0" and "b < 0"
  shows "a + b < 0"
proof -
  have "a + b < 0 + 0"
    using assms by (rule add_le_less_mono)
  then show ?thesis by simp
qed

lemma add_nonpos_nonpos:
  assumes "a \<le> 0" and "b \<le> 0"
  shows "a + b \<le> 0"
proof -
  have "a + b \<le> 0 + 0"
    using assms by (rule add_mono)
  then show ?thesis by simp
qed

end

class pordered_ab_group_add =
  ab_group_add + pordered_ab_semigroup_add
begin

subclass pordered_cancel_ab_semigroup_add ..

subclass pordered_ab_semigroup_add_imp_le
proof unfold_locales
  fix a b c :: 'a
  assume "c + a \<le> c + b"
  hence "(-c) + (c + a) \<le> (-c) + (c + b)" by (rule add_left_mono)
  hence "((-c) + c) + a \<le> ((-c) + c) + b" by (simp only: add_assoc)
  thus "a \<le> b" by simp
qed

subclass pordered_comm_monoid_add ..

lemma max_diff_distrib_left:
  shows "max x y - z = max (x - z) (y - z)"
  by (simp add: diff_minus, rule max_add_distrib_left) 

lemma min_diff_distrib_left:
  shows "min x y - z = min (x - z) (y - z)"
  by (simp add: diff_minus, rule min_add_distrib_left) 

lemma le_imp_neg_le:
  assumes "a \<le> b"
  shows "-b \<le> -a"
proof -
  have "-a+a \<le> -a+b"
    using `a \<le> b` by (rule add_left_mono) 
  hence "0 \<le> -a+b"
    by simp
  hence "0 + (-b) \<le> (-a + b) + (-b)"
    by (rule add_right_mono) 
  thus ?thesis
    by (simp add: add_assoc)
qed

lemma neg_le_iff_le [simp]: "- b \<le> - a \<longleftrightarrow> a \<le> b"
proof 
  assume "- b \<le> - a"
  hence "- (- a) \<le> - (- b)"
    by (rule le_imp_neg_le)
  thus "a\<le>b" by simp
next
  assume "a\<le>b"
  thus "-b \<le> -a" by (rule le_imp_neg_le)
qed

lemma neg_le_0_iff_le [simp]: "- a \<le> 0 \<longleftrightarrow> 0 \<le> a"
  by (subst neg_le_iff_le [symmetric], simp)

lemma neg_0_le_iff_le [simp]: "0 \<le> - a \<longleftrightarrow> a \<le> 0"
  by (subst neg_le_iff_le [symmetric], simp)

lemma neg_less_iff_less [simp]: "- b < - a \<longleftrightarrow> a < b"
  by (force simp add: less_le) 

lemma neg_less_0_iff_less [simp]: "- a < 0 \<longleftrightarrow> 0 < a"
  by (subst neg_less_iff_less [symmetric], simp)

lemma neg_0_less_iff_less [simp]: "0 < - a \<longleftrightarrow> a < 0"
  by (subst neg_less_iff_less [symmetric], simp)

text{*The next several equations can make the simplifier loop!*}

lemma less_minus_iff: "a < - b \<longleftrightarrow> b < - a"
proof -
  have "(- (-a) < - b) = (b < - a)" by (rule neg_less_iff_less)
  thus ?thesis by simp
qed

lemma minus_less_iff: "- a < b \<longleftrightarrow> - b < a"
proof -
  have "(- a < - (-b)) = (- b < a)" by (rule neg_less_iff_less)
  thus ?thesis by simp
qed

lemma le_minus_iff: "a \<le> - b \<longleftrightarrow> b \<le> - a"
proof -
  have mm: "!! a (b::'a). (-(-a)) < -b \<Longrightarrow> -(-b) < -a" by (simp only: minus_less_iff)
  have "(- (- a) <= -b) = (b <= - a)" 
    apply (auto simp only: le_less)
    apply (drule mm)
    apply (simp_all)
    apply (drule mm[simplified], assumption)
    done
  then show ?thesis by simp
qed

lemma minus_le_iff: "- a \<le> b \<longleftrightarrow> - b \<le> a"
  by (auto simp add: le_less minus_less_iff)

lemma less_iff_diff_less_0: "a < b \<longleftrightarrow> a - b < 0"
proof -
  have  "(a < b) = (a + (- b) < b + (-b))"  
    by (simp only: add_less_cancel_right)
  also have "... =  (a - b < 0)" by (simp add: diff_minus)
  finally show ?thesis .
qed

lemma diff_less_eq: "a - b < c \<longleftrightarrow> a < c + b"
apply (subst less_iff_diff_less_0 [of a])
apply (rule less_iff_diff_less_0 [of _ c, THEN ssubst])
apply (simp add: diff_minus add_ac)
done

lemma less_diff_eq: "a < c - b \<longleftrightarrow> a + b < c"
apply (subst less_iff_diff_less_0 [of "plus a b"])
apply (subst less_iff_diff_less_0 [of a])
apply (simp add: diff_minus add_ac)
done

lemma diff_le_eq: "a - b \<le> c \<longleftrightarrow> a \<le> c + b"
  by (auto simp add: le_less diff_less_eq diff_add_cancel add_diff_cancel)

lemma le_diff_eq: "a \<le> c - b \<longleftrightarrow> a + b \<le> c"
  by (auto simp add: le_less less_diff_eq diff_add_cancel add_diff_cancel)

lemmas compare_rls =
       diff_minus [symmetric]
       add_diff_eq diff_add_eq diff_diff_eq diff_diff_eq2
       diff_less_eq less_diff_eq diff_le_eq le_diff_eq
       diff_eq_eq eq_diff_eq

text{*This list of rewrites simplifies (in)equalities by bringing subtractions
  to the top and then moving negative terms to the other side.
  Use with @{text add_ac}*}
lemmas (in -) compare_rls =
       diff_minus [symmetric]
       add_diff_eq diff_add_eq diff_diff_eq diff_diff_eq2
       diff_less_eq less_diff_eq diff_le_eq le_diff_eq
       diff_eq_eq eq_diff_eq

lemma le_iff_diff_le_0: "a \<le> b \<longleftrightarrow> a - b \<le> 0"
  by (simp add: compare_rls)

lemmas group_simps =
  add_ac
  add_diff_eq diff_add_eq diff_diff_eq diff_diff_eq2
  diff_eq_eq eq_diff_eq diff_minus [symmetric] uminus_add_conv_diff
  diff_less_eq less_diff_eq diff_le_eq le_diff_eq

end

lemmas group_simps =
  mult_ac
  add_ac
  add_diff_eq diff_add_eq diff_diff_eq diff_diff_eq2
  diff_eq_eq eq_diff_eq diff_minus [symmetric] uminus_add_conv_diff
  diff_less_eq less_diff_eq diff_le_eq le_diff_eq

class ordered_ab_semigroup_add =
  linorder + pordered_ab_semigroup_add

class ordered_cancel_ab_semigroup_add =
  linorder + pordered_cancel_ab_semigroup_add
begin

subclass ordered_ab_semigroup_add ..

subclass pordered_ab_semigroup_add_imp_le
proof unfold_locales
  fix a b c :: 'a
  assume le: "c + a <= c + b"  
  show "a <= b"
  proof (rule ccontr)
    assume w: "~ a \<le> b"
    hence "b <= a" by (simp add: linorder_not_le)
    hence le2: "c + b <= c + a" by (rule add_left_mono)
    have "a = b" 
      apply (insert le)
      apply (insert le2)
      apply (drule antisym, simp_all)
      done
    with w show False 
      by (simp add: linorder_not_le [symmetric])
  qed
qed

end

class ordered_ab_group_add =
  linorder + pordered_ab_group_add
begin

subclass ordered_cancel_ab_semigroup_add ..

lemma neg_less_eq_nonneg:
  "- a \<le> a \<longleftrightarrow> 0 \<le> a"
proof
  assume A: "- a \<le> a" show "0 \<le> a"
  proof (rule classical)
    assume "\<not> 0 \<le> a"
    then have "a < 0" by auto
    with A have "- a < 0" by (rule le_less_trans)
    then show ?thesis by auto
  qed
next
  assume A: "0 \<le> a" show "- a \<le> a"
  proof (rule order_trans)
    show "- a \<le> 0" using A by (simp add: minus_le_iff)
  next
    show "0 \<le> a" using A .
  qed
qed
  
lemma less_eq_neg_nonpos:
  "a \<le> - a \<longleftrightarrow> a \<le> 0"
proof
  assume A: "a \<le> - a" show "a \<le> 0"
  proof (rule classical)
    assume "\<not> a \<le> 0"
    then have "0 < a" by auto
    then have "0 < - a" using A by (rule less_le_trans)
    then show ?thesis by auto
  qed
next
  assume A: "a \<le> 0" show "a \<le> - a"
  proof (rule order_trans)
    show "0 \<le> - a" using A by (simp add: minus_le_iff)
  next
    show "a \<le> 0" using A .
  qed
qed

lemma equal_neg_zero:
  "a = - a \<longleftrightarrow> a = 0"
proof
  assume "a = 0" then show "a = - a" by simp
next
  assume A: "a = - a" show "a = 0"
  proof (cases "0 \<le> a")
    case True with A have "0 \<le> - a" by auto
    with le_minus_iff have "a \<le> 0" by simp
    with True show ?thesis by (auto intro: order_trans)
  next
    case False then have B: "a \<le> 0" by auto
    with A have "- a \<le> 0" by auto
    with B show ?thesis by (auto intro: order_trans)
  qed
qed

lemma neg_equal_zero:
  "- a = a \<longleftrightarrow> a = 0"
  unfolding equal_neg_zero [symmetric] by auto

end

-- {* FIXME localize the following *}

lemma add_increasing:
  fixes c :: "'a::{pordered_ab_semigroup_add_imp_le, comm_monoid_add}"
  shows  "[|0\<le>a; b\<le>c|] ==> b \<le> a + c"
by (insert add_mono [of 0 a b c], simp)

lemma add_increasing2:
  fixes c :: "'a::{pordered_ab_semigroup_add_imp_le, comm_monoid_add}"
  shows  "[|0\<le>c; b\<le>a|] ==> b \<le> a + c"
by (simp add:add_increasing add_commute[of a])

lemma add_strict_increasing:
  fixes c :: "'a::{pordered_ab_semigroup_add_imp_le, comm_monoid_add}"
  shows "[|0<a; b\<le>c|] ==> b < a + c"
by (insert add_less_le_mono [of 0 a b c], simp)

lemma add_strict_increasing2:
  fixes c :: "'a::{pordered_ab_semigroup_add_imp_le, comm_monoid_add}"
  shows "[|0\<le>a; b<c|] ==> b < a + c"
by (insert add_le_less_mono [of 0 a b c], simp)


class pordered_ab_group_add_abs = pordered_ab_group_add + abs +
  assumes abs_ge_zero [simp]: "\<bar>a\<bar> \<ge> 0"
    and abs_ge_self: "a \<le> \<bar>a\<bar>"
    and abs_leI: "a \<le> b \<Longrightarrow> - a \<le> b \<Longrightarrow> \<bar>a\<bar> \<le> b"
    and abs_minus_cancel [simp]: "\<bar>-a\<bar> = \<bar>a\<bar>"
    and abs_triangle_ineq: "\<bar>a + b\<bar> \<le> \<bar>a\<bar> + \<bar>b\<bar>"
begin

lemma abs_minus_le_zero: "- \<bar>a\<bar> \<le> 0"
  unfolding neg_le_0_iff_le by simp

lemma abs_of_nonneg [simp]:
  assumes nonneg: "0 \<le> a"
  shows "\<bar>a\<bar> = a"
proof (rule antisym)
  from nonneg le_imp_neg_le have "- a \<le> 0" by simp
  from this nonneg have "- a \<le> a" by (rule order_trans)
  then show "\<bar>a\<bar> \<le> a" by (auto intro: abs_leI)
qed (rule abs_ge_self)

lemma abs_idempotent [simp]: "\<bar>\<bar>a\<bar>\<bar> = \<bar>a\<bar>"
  by (rule antisym)
    (auto intro!: abs_ge_self abs_leI order_trans [of "uminus (abs a)" zero "abs a"])

lemma abs_eq_0 [simp]: "\<bar>a\<bar> = 0 \<longleftrightarrow> a = 0"
proof -
  have "\<bar>a\<bar> = 0 \<Longrightarrow> a = 0"
  proof (rule antisym)
    assume zero: "\<bar>a\<bar> = 0"
    with abs_ge_self show "a \<le> 0" by auto
    from zero have "\<bar>-a\<bar> = 0" by simp
    with abs_ge_self [of "uminus a"] have "- a \<le> 0" by auto
    with neg_le_0_iff_le show "0 \<le> a" by auto
  qed
  then show ?thesis by auto
qed

lemma abs_zero [simp]: "\<bar>0\<bar> = 0"
  by simp

lemma abs_0_eq [simp, noatp]: "0 = \<bar>a\<bar> \<longleftrightarrow> a = 0"
proof -
  have "0 = \<bar>a\<bar> \<longleftrightarrow> \<bar>a\<bar> = 0" by (simp only: eq_ac)
  thus ?thesis by simp
qed

lemma abs_le_zero_iff [simp]: "\<bar>a\<bar> \<le> 0 \<longleftrightarrow> a = 0" 
proof
  assume "\<bar>a\<bar> \<le> 0"
  then have "\<bar>a\<bar> = 0" by (rule antisym) simp
  thus "a = 0" by simp
next
  assume "a = 0"
  thus "\<bar>a\<bar> \<le> 0" by simp
qed

lemma zero_less_abs_iff [simp]: "0 < \<bar>a\<bar> \<longleftrightarrow> a \<noteq> 0"
  by (simp add: less_le)

lemma abs_not_less_zero [simp]: "\<not> \<bar>a\<bar> < 0"
proof -
  have a: "\<And>x y. x \<le> y \<Longrightarrow> \<not> y < x" by auto
  show ?thesis by (simp add: a)
qed

lemma abs_ge_minus_self: "- a \<le> \<bar>a\<bar>"
proof -
  have "- a \<le> \<bar>-a\<bar>" by (rule abs_ge_self)
  then show ?thesis by simp
qed

lemma abs_minus_commute: 
  "\<bar>a - b\<bar> = \<bar>b - a\<bar>"
proof -
  have "\<bar>a - b\<bar> = \<bar>- (a - b)\<bar>" by (simp only: abs_minus_cancel)
  also have "... = \<bar>b - a\<bar>" by simp
  finally show ?thesis .
qed

lemma abs_of_pos: "0 < a \<Longrightarrow> \<bar>a\<bar> = a"
  by (rule abs_of_nonneg, rule less_imp_le)

lemma abs_of_nonpos [simp]:
  assumes "a \<le> 0"
  shows "\<bar>a\<bar> = - a"
proof -
  let ?b = "- a"
  have "- ?b \<le> 0 \<Longrightarrow> \<bar>- ?b\<bar> = - (- ?b)"
  unfolding abs_minus_cancel [of "?b"]
  unfolding neg_le_0_iff_le [of "?b"]
  unfolding minus_minus by (erule abs_of_nonneg)
  then show ?thesis using assms by auto
qed
  
lemma abs_of_neg: "a < 0 \<Longrightarrow> \<bar>a\<bar> = - a"
  by (rule abs_of_nonpos, rule less_imp_le)

lemma abs_le_D1: "\<bar>a\<bar> \<le> b \<Longrightarrow> a \<le> b"
  by (insert abs_ge_self, blast intro: order_trans)

lemma abs_le_D2: "\<bar>a\<bar> \<le> b \<Longrightarrow> - a \<le> b"
  by (insert abs_le_D1 [of "uminus a"], simp)

lemma abs_le_iff: "\<bar>a\<bar> \<le> b \<longleftrightarrow> a \<le> b \<and> - a \<le> b"
  by (blast intro: abs_leI dest: abs_le_D1 abs_le_D2)

lemma abs_triangle_ineq2: "\<bar>a\<bar> - \<bar>b\<bar> \<le> \<bar>a - b\<bar>"
  apply (simp add: compare_rls)
  apply (subgoal_tac "abs a = abs (plus (minus a b) b)")
  apply (erule ssubst)
  apply (rule abs_triangle_ineq)
  apply (rule arg_cong) back
  apply (simp add: compare_rls)
done

lemma abs_triangle_ineq3: "\<bar>\<bar>a\<bar> - \<bar>b\<bar>\<bar> \<le> \<bar>a - b\<bar>"
  apply (subst abs_le_iff)
  apply auto
  apply (rule abs_triangle_ineq2)
  apply (subst abs_minus_commute)
  apply (rule abs_triangle_ineq2)
done

lemma abs_triangle_ineq4: "\<bar>a - b\<bar> \<le> \<bar>a\<bar> + \<bar>b\<bar>"
proof -
  have "abs(a - b) = abs(a + - b)"
    by (subst diff_minus, rule refl)
  also have "... <= abs a + abs (- b)"
    by (rule abs_triangle_ineq)
  finally show ?thesis
    by simp
qed

lemma abs_diff_triangle_ineq: "\<bar>a + b - (c + d)\<bar> \<le> \<bar>a - c\<bar> + \<bar>b - d\<bar>"
proof -
  have "\<bar>a + b - (c+d)\<bar> = \<bar>(a-c) + (b-d)\<bar>" by (simp add: diff_minus add_ac)
  also have "... \<le> \<bar>a-c\<bar> + \<bar>b-d\<bar>" by (rule abs_triangle_ineq)
  finally show ?thesis .
qed

lemma abs_add_abs [simp]:
  "\<bar>\<bar>a\<bar> + \<bar>b\<bar>\<bar> = \<bar>a\<bar> + \<bar>b\<bar>" (is "?L = ?R")
proof (rule antisym)
  show "?L \<ge> ?R" by(rule abs_ge_self)
next
  have "?L \<le> \<bar>\<bar>a\<bar>\<bar> + \<bar>\<bar>b\<bar>\<bar>" by(rule abs_triangle_ineq)
  also have "\<dots> = ?R" by simp
  finally show "?L \<le> ?R" .
qed

end


subsection {* Lattice Ordered (Abelian) Groups *}

class lordered_ab_group_add_meet = pordered_ab_group_add + lower_semilattice
begin

lemma add_inf_distrib_left:
  "a + inf b c = inf (a + b) (a + c)"
apply (rule antisym)
apply (simp_all add: le_infI)
apply (rule add_le_imp_le_left [of "uminus a"])
apply (simp only: add_assoc [symmetric], simp)
apply rule
apply (rule add_le_imp_le_left[of "a"], simp only: add_assoc[symmetric], simp)+
done

lemma add_inf_distrib_right:
  "inf a b + c = inf (a + c) (b + c)"
proof -
  have "c + inf a b = inf (c+a) (c+b)" by (simp add: add_inf_distrib_left)
  thus ?thesis by (simp add: add_commute)
qed

end

class lordered_ab_group_add_join = pordered_ab_group_add + upper_semilattice
begin

lemma add_sup_distrib_left:
  "a + sup b c = sup (a + b) (a + c)" 
apply (rule antisym)
apply (rule add_le_imp_le_left [of "uminus a"])
apply (simp only: add_assoc[symmetric], simp)
apply rule
apply (rule add_le_imp_le_left [of "a"], simp only: add_assoc[symmetric], simp)+
apply (rule le_supI)
apply (simp_all)
done

lemma add_sup_distrib_right:
  "sup a b + c = sup (a+c) (b+c)"
proof -
  have "c + sup a b = sup (c+a) (c+b)" by (simp add: add_sup_distrib_left)
  thus ?thesis by (simp add: add_commute)
qed

end

class lordered_ab_group_add = pordered_ab_group_add + lattice
begin

subclass lordered_ab_group_add_meet ..
subclass lordered_ab_group_add_join ..

lemmas add_sup_inf_distribs = add_inf_distrib_right add_inf_distrib_left add_sup_distrib_right add_sup_distrib_left

lemma inf_eq_neg_sup: "inf a b = - sup (-a) (-b)"
proof (rule inf_unique)
  fix a b :: 'a
  show "- sup (-a) (-b) \<le> a"
    by (rule add_le_imp_le_right [of _ "sup (uminus a) (uminus b)"])
      (simp, simp add: add_sup_distrib_left)
next
  fix a b :: 'a
  show "- sup (-a) (-b) \<le> b"
    by (rule add_le_imp_le_right [of _ "sup (uminus a) (uminus b)"])
      (simp, simp add: add_sup_distrib_left)
next
  fix a b c :: 'a
  assume "a \<le> b" "a \<le> c"
  then show "a \<le> - sup (-b) (-c)" by (subst neg_le_iff_le [symmetric])
    (simp add: le_supI)
qed
  
lemma sup_eq_neg_inf: "sup a b = - inf (-a) (-b)"
proof (rule sup_unique)
  fix a b :: 'a
  show "a \<le> - inf (-a) (-b)"
    by (rule add_le_imp_le_right [of _ "inf (uminus a) (uminus b)"])
      (simp, simp add: add_inf_distrib_left)
next
  fix a b :: 'a
  show "b \<le> - inf (-a) (-b)"
    by (rule add_le_imp_le_right [of _ "inf (uminus a) (uminus b)"])
      (simp, simp add: add_inf_distrib_left)
next
  fix a b c :: 'a
  assume "a \<le> c" "b \<le> c"
  then show "- inf (-a) (-b) \<le> c" by (subst neg_le_iff_le [symmetric])
    (simp add: le_infI)
qed

lemma neg_inf_eq_sup: "- inf a b = sup (-a) (-b)"
  by (simp add: inf_eq_neg_sup)

lemma neg_sup_eq_inf: "- sup a b = inf (-a) (-b)"
  by (simp add: sup_eq_neg_inf)

lemma add_eq_inf_sup: "a + b = sup a b + inf a b"
proof -
  have "0 = - inf 0 (a-b) + inf (a-b) 0" by (simp add: inf_commute)
  hence "0 = sup 0 (b-a) + inf (a-b) 0" by (simp add: inf_eq_neg_sup)
  hence "0 = (-a + sup a b) + (inf a b + (-b))"
    apply (simp add: add_sup_distrib_left add_inf_distrib_right)
    by (simp add: diff_minus add_commute)
  thus ?thesis
    apply (simp add: compare_rls)
    apply (subst add_left_cancel [symmetric, of "plus a b" "plus (sup a b) (inf a b)" "uminus a"])
    apply (simp only: add_assoc, simp add: add_assoc[symmetric])
    done
qed

subsection {* Positive Part, Negative Part, Absolute Value *}

definition
  nprt :: "'a \<Rightarrow> 'a" where
  "nprt x = inf x 0"

definition
  pprt :: "'a \<Rightarrow> 'a" where
  "pprt x = sup x 0"

lemma pprt_neg: "pprt (- x) = - nprt x"
proof -
  have "sup (- x) 0 = sup (- x) (- 0)" unfolding minus_zero ..
  also have "\<dots> = - inf x 0" unfolding neg_inf_eq_sup ..
  finally have "sup (- x) 0 = - inf x 0" .
  then show ?thesis unfolding pprt_def nprt_def .
qed

lemma nprt_neg: "nprt (- x) = - pprt x"
proof -
  from pprt_neg have "pprt (- (- x)) = - nprt (- x)" .
  then have "pprt x = - nprt (- x)" by simp
  then show ?thesis by simp
qed

lemma prts: "a = pprt a + nprt a"
  by (simp add: pprt_def nprt_def add_eq_inf_sup[symmetric])

lemma zero_le_pprt[simp]: "0 \<le> pprt a"
  by (simp add: pprt_def)

lemma nprt_le_zero[simp]: "nprt a \<le> 0"
  by (simp add: nprt_def)

lemma le_eq_neg: "a \<le> - b \<longleftrightarrow> a + b \<le> 0" (is "?l = ?r")
proof -
  have a: "?l \<longrightarrow> ?r"
    apply (auto)
    apply (rule add_le_imp_le_right[of _ "uminus b" _])
    apply (simp add: add_assoc)
    done
  have b: "?r \<longrightarrow> ?l"
    apply (auto)
    apply (rule add_le_imp_le_right[of _ "b" _])
    apply (simp)
    done
  from a b show ?thesis by blast
qed

lemma pprt_0[simp]: "pprt 0 = 0" by (simp add: pprt_def)
lemma nprt_0[simp]: "nprt 0 = 0" by (simp add: nprt_def)

lemma pprt_eq_id [simp, noatp]: "0 \<le> x \<Longrightarrow> pprt x = x"
  by (simp add: pprt_def le_iff_sup sup_ACI)

lemma nprt_eq_id [simp, noatp]: "x \<le> 0 \<Longrightarrow> nprt x = x"
  by (simp add: nprt_def le_iff_inf inf_ACI)

lemma pprt_eq_0 [simp, noatp]: "x \<le> 0 \<Longrightarrow> pprt x = 0"
  by (simp add: pprt_def le_iff_sup sup_ACI)

lemma nprt_eq_0 [simp, noatp]: "0 \<le> x \<Longrightarrow> nprt x = 0"
  by (simp add: nprt_def le_iff_inf inf_ACI)

lemma sup_0_imp_0: "sup a (- a) = 0 \<Longrightarrow> a = 0"
proof -
  {
    fix a::'a
    assume hyp: "sup a (-a) = 0"
    hence "sup a (-a) + a = a" by (simp)
    hence "sup (a+a) 0 = a" by (simp add: add_sup_distrib_right) 
    hence "sup (a+a) 0 <= a" by (simp)
    hence "0 <= a" by (blast intro: order_trans inf_sup_ord)
  }
  note p = this
  assume hyp:"sup a (-a) = 0"
  hence hyp2:"sup (-a) (-(-a)) = 0" by (simp add: sup_commute)
  from p[OF hyp] p[OF hyp2] show "a = 0" by simp
qed

lemma inf_0_imp_0: "inf a (-a) = 0 \<Longrightarrow> a = 0"
apply (simp add: inf_eq_neg_sup)
apply (simp add: sup_commute)
apply (erule sup_0_imp_0)
done

lemma inf_0_eq_0 [simp, noatp]: "inf a (- a) = 0 \<longleftrightarrow> a = 0"
  by (rule, erule inf_0_imp_0) simp

lemma sup_0_eq_0 [simp, noatp]: "sup a (- a) = 0 \<longleftrightarrow> a = 0"
  by (rule, erule sup_0_imp_0) simp

lemma zero_le_double_add_iff_zero_le_single_add [simp]:
  "0 \<le> a + a \<longleftrightarrow> 0 \<le> a"
proof
  assume "0 <= a + a"
  hence a:"inf (a+a) 0 = 0" by (simp add: le_iff_inf inf_commute)
  have "(inf a 0)+(inf a 0) = inf (inf (a+a) 0) a" (is "?l=_")
    by (simp add: add_sup_inf_distribs inf_ACI)
  hence "?l = 0 + inf a 0" by (simp add: a, simp add: inf_commute)
  hence "inf a 0 = 0" by (simp only: add_right_cancel)
  then show "0 <= a" by (simp add: le_iff_inf inf_commute)    
next  
  assume a: "0 <= a"
  show "0 <= a + a" by (simp add: add_mono[OF a a, simplified])
qed

lemma double_zero: "a + a = 0 \<longleftrightarrow> a = 0"
proof
  assume assm: "a + a = 0"
  then have "a + a + - a = - a" by simp
  then have "a + (a + - a) = - a" by (simp only: add_assoc)
  then have a: "- a = a" by simp (*FIXME tune proof*)
  show "a = 0" apply (rule antisym)
  apply (unfold neg_le_iff_le [symmetric, of a])
  unfolding a apply simp
  unfolding zero_le_double_add_iff_zero_le_single_add [symmetric, of a]
  unfolding assm unfolding le_less apply simp_all done
next
  assume "a = 0" then show "a + a = 0" by simp
qed

lemma zero_less_double_add_iff_zero_less_single_add:
  "0 < a + a \<longleftrightarrow> 0 < a"
proof (cases "a = 0")
  case True then show ?thesis by auto
next
  case False then show ?thesis (*FIXME tune proof*)
  unfolding less_le apply simp apply rule
  apply clarify
  apply rule
  apply assumption
  apply (rule notI)
  unfolding double_zero [symmetric, of a] apply simp
  done
qed

lemma double_add_le_zero_iff_single_add_le_zero [simp]:
  "a + a \<le> 0 \<longleftrightarrow> a \<le> 0" 
proof -
  have "a + a \<le> 0 \<longleftrightarrow> 0 \<le> - (a + a)" by (subst le_minus_iff, simp)
  moreover have "\<dots> \<longleftrightarrow> a \<le> 0" by (simp add: zero_le_double_add_iff_zero_le_single_add)
  ultimately show ?thesis by blast
qed

lemma double_add_less_zero_iff_single_less_zero [simp]:
  "a + a < 0 \<longleftrightarrow> a < 0"
proof -
  have "a + a < 0 \<longleftrightarrow> 0 < - (a + a)" by (subst less_minus_iff, simp)
  moreover have "\<dots> \<longleftrightarrow> a < 0" by (simp add: zero_less_double_add_iff_zero_less_single_add)
  ultimately show ?thesis by blast
qed

declare neg_inf_eq_sup [simp] neg_sup_eq_inf [simp]

lemma le_minus_self_iff: "a \<le> - a \<longleftrightarrow> a \<le> 0"
proof -
  from add_le_cancel_left [of "uminus a" "plus a a" zero]
  have "(a <= -a) = (a+a <= 0)" 
    by (simp add: add_assoc[symmetric])
  thus ?thesis by simp
qed

lemma minus_le_self_iff: "- a \<le> a \<longleftrightarrow> 0 \<le> a"
proof -
  from add_le_cancel_left [of "uminus a" zero "plus a a"]
  have "(-a <= a) = (0 <= a+a)" 
    by (simp add: add_assoc[symmetric])
  thus ?thesis by simp
qed

lemma zero_le_iff_zero_nprt: "0 \<le> a \<longleftrightarrow> nprt a = 0"
  by (simp add: le_iff_inf nprt_def inf_commute)

lemma le_zero_iff_zero_pprt: "a \<le> 0 \<longleftrightarrow> pprt a = 0"
  by (simp add: le_iff_sup pprt_def sup_commute)

lemma le_zero_iff_pprt_id: "0 \<le> a \<longleftrightarrow> pprt a = a"
  by (simp add: le_iff_sup pprt_def sup_commute)

lemma zero_le_iff_nprt_id: "a \<le> 0 \<longleftrightarrow> nprt a = a"
  by (simp add: le_iff_inf nprt_def inf_commute)

lemma pprt_mono [simp, noatp]: "a \<le> b \<Longrightarrow> pprt a \<le> pprt b"
  by (simp add: le_iff_sup pprt_def sup_ACI sup_assoc [symmetric, of a])

lemma nprt_mono [simp, noatp]: "a \<le> b \<Longrightarrow> nprt a \<le> nprt b"
  by (simp add: le_iff_inf nprt_def inf_ACI inf_assoc [symmetric, of a])

end

lemmas add_sup_inf_distribs = add_inf_distrib_right add_inf_distrib_left add_sup_distrib_right add_sup_distrib_left


class lordered_ab_group_add_abs = lordered_ab_group_add + abs +
  assumes abs_lattice: "\<bar>a\<bar> = sup a (- a)"
begin

lemma abs_prts: "\<bar>a\<bar> = pprt a - nprt a"
proof -
  have "0 \<le> \<bar>a\<bar>"
  proof -
    have a: "a \<le> \<bar>a\<bar>" and b: "- a \<le> \<bar>a\<bar>" by (auto simp add: abs_lattice)
    show ?thesis by (rule add_mono [OF a b, simplified])
  qed
  then have "0 \<le> sup a (- a)" unfolding abs_lattice .
  then have "sup (sup a (- a)) 0 = sup a (- a)" by (rule sup_absorb1)
  then show ?thesis
    by (simp add: add_sup_inf_distribs sup_ACI
      pprt_def nprt_def diff_minus abs_lattice)
qed

subclass pordered_ab_group_add_abs
proof -
  have abs_ge_zero [simp]: "\<And>a. 0 \<le> \<bar>a\<bar>"
  proof -
    fix a b
    have a: "a \<le> \<bar>a\<bar>" and b: "- a \<le> \<bar>a\<bar>" by (auto simp add: abs_lattice)
    show "0 \<le> \<bar>a\<bar>" by (rule add_mono [OF a b, simplified])
  qed
  have abs_leI: "\<And>a b. a \<le> b \<Longrightarrow> - a \<le> b \<Longrightarrow> \<bar>a\<bar> \<le> b"
    by (simp add: abs_lattice le_supI)
  show ?thesis
  proof unfold_locales
    fix a
    show "0 \<le> \<bar>a\<bar>" by simp
  next
    fix a
    show "a \<le> \<bar>a\<bar>"
      by (auto simp add: abs_lattice)
  next
    fix a
    show "\<bar>-a\<bar> = \<bar>a\<bar>"
      by (simp add: abs_lattice sup_commute)
  next
    fix a b
    show "a \<le> b \<Longrightarrow> - a \<le> b \<Longrightarrow> \<bar>a\<bar> \<le> b" by (erule abs_leI)
  next
    fix a b
    show "\<bar>a + b\<bar> \<le> \<bar>a\<bar> + \<bar>b\<bar>"
    proof -
      have g:"abs a + abs b = sup (a+b) (sup (-a-b) (sup (-a+b) (a + (-b))))" (is "_=sup ?m ?n")
        by (simp add: abs_lattice add_sup_inf_distribs sup_ACI diff_minus)
      have a:"a+b <= sup ?m ?n" by (simp)
      have b:"-a-b <= ?n" by (simp) 
      have c:"?n <= sup ?m ?n" by (simp)
      from b c have d: "-a-b <= sup ?m ?n" by(rule order_trans)
      have e:"-a-b = -(a+b)" by (simp add: diff_minus)
      from a d e have "abs(a+b) <= sup ?m ?n" 
        by (drule_tac abs_leI, auto)
      with g[symmetric] show ?thesis by simp
    qed
  qed auto
qed

end

lemma sup_eq_if:
  fixes a :: "'a\<Colon>{lordered_ab_group_add, linorder}"
  shows "sup a (- a) = (if a < 0 then - a else a)"
proof -
  note add_le_cancel_right [of a a "- a", symmetric, simplified]
  moreover note add_le_cancel_right [of "-a" a a, symmetric, simplified]
  then show ?thesis by (auto simp: sup_max max_def)
qed

lemma abs_if_lattice:
  fixes a :: "'a\<Colon>{lordered_ab_group_add_abs, linorder}"
  shows "\<bar>a\<bar> = (if a < 0 then - a else a)"
  by auto


text {* Needed for abelian cancellation simprocs: *}

lemma add_cancel_21: "((x::'a::ab_group_add) + (y + z) = y + u) = (x + z = u)"
apply (subst add_left_commute)
apply (subst add_left_cancel)
apply simp
done

lemma add_cancel_end: "(x + (y + z) = y) = (x = - (z::'a::ab_group_add))"
apply (subst add_cancel_21[of _ _ _ 0, simplified])
apply (simp add: add_right_cancel[symmetric, of "x" "-z" "z", simplified])
done

lemma less_eqI: "(x::'a::pordered_ab_group_add) - y = x' - y' \<Longrightarrow> (x < y) = (x' < y')"
by (simp add: less_iff_diff_less_0[of x y] less_iff_diff_less_0[of x' y'])

lemma le_eqI: "(x::'a::pordered_ab_group_add) - y = x' - y' \<Longrightarrow> (y <= x) = (y' <= x')"
apply (simp add: le_iff_diff_le_0[of y x] le_iff_diff_le_0[of  y' x'])
apply (simp add: neg_le_iff_le[symmetric, of "y-x" 0] neg_le_iff_le[symmetric, of "y'-x'" 0])
done

lemma eq_eqI: "(x::'a::ab_group_add) - y = x' - y' \<Longrightarrow> (x = y) = (x' = y')"
by (simp add: eq_iff_diff_eq_0[of x y] eq_iff_diff_eq_0[of x' y'])

lemma diff_def: "(x::'a::ab_group_add) - y == x + (-y)"
by (simp add: diff_minus)

lemma add_minus_cancel: "(a::'a::ab_group_add) + (-a + b) = b"
by (simp add: add_assoc[symmetric])

lemma le_add_right_mono: 
  assumes 
  "a <= b + (c::'a::pordered_ab_group_add)"
  "c <= d"    
  shows "a <= b + d"
  apply (rule_tac order_trans[where y = "b+c"])
  apply (simp_all add: prems)
  done

lemma estimate_by_abs:
  "a + b <= (c::'a::lordered_ab_group_add_abs) \<Longrightarrow> a <= c + abs b" 
proof -
  assume "a+b <= c"
  hence 2: "a <= c+(-b)" by (simp add: group_simps)
  have 3: "(-b) <= abs b" by (rule abs_ge_minus_self)
  show ?thesis by (rule le_add_right_mono[OF 2 3])
qed

subsection {* Tools setup *}

lemma add_mono_thms_ordered_semiring [noatp]:
  fixes i j k :: "'a\<Colon>pordered_ab_semigroup_add"
  shows "i \<le> j \<and> k \<le> l \<Longrightarrow> i + k \<le> j + l"
    and "i = j \<and> k \<le> l \<Longrightarrow> i + k \<le> j + l"
    and "i \<le> j \<and> k = l \<Longrightarrow> i + k \<le> j + l"
    and "i = j \<and> k = l \<Longrightarrow> i + k = j + l"
by (rule add_mono, clarify+)+

lemma add_mono_thms_ordered_field [noatp]:
  fixes i j k :: "'a\<Colon>pordered_cancel_ab_semigroup_add"
  shows "i < j \<and> k = l \<Longrightarrow> i + k < j + l"
    and "i = j \<and> k < l \<Longrightarrow> i + k < j + l"
    and "i < j \<and> k \<le> l \<Longrightarrow> i + k < j + l"
    and "i \<le> j \<and> k < l \<Longrightarrow> i + k < j + l"
    and "i < j \<and> k < l \<Longrightarrow> i + k < j + l"
by (auto intro: add_strict_right_mono add_strict_left_mono
  add_less_le_mono add_le_less_mono add_strict_mono)

text{*Simplification of @{term "x-y < 0"}, etc.*}
lemmas diff_less_0_iff_less [simp] = less_iff_diff_less_0 [symmetric]
lemmas diff_eq_0_iff_eq [simp, noatp] = eq_iff_diff_eq_0 [symmetric]
lemmas diff_le_0_iff_le [simp] = le_iff_diff_le_0 [symmetric]

ML {*
structure ab_group_add_cancel = Abel_Cancel
(

(* term order for abelian groups *)

fun agrp_ord (Const (a, _)) = find_index (fn a' => a = a')
      [@{const_name HOL.zero}, @{const_name HOL.plus},
        @{const_name HOL.uminus}, @{const_name HOL.minus}]
  | agrp_ord _ = ~1;

fun termless_agrp (a, b) = (Term.term_lpo agrp_ord (a, b) = LESS);

local
  val ac1 = mk_meta_eq @{thm add_assoc};
  val ac2 = mk_meta_eq @{thm add_commute};
  val ac3 = mk_meta_eq @{thm add_left_commute};
  fun solve_add_ac thy _ (_ $ (Const (@{const_name HOL.plus},_) $ _ $ _) $ _) =
        SOME ac1
    | solve_add_ac thy _ (_ $ x $ (Const (@{const_name HOL.plus},_) $ y $ z)) =
        if termless_agrp (y, x) then SOME ac3 else NONE
    | solve_add_ac thy _ (_ $ x $ y) =
        if termless_agrp (y, x) then SOME ac2 else NONE
    | solve_add_ac thy _ _ = NONE
in
  val add_ac_proc = Simplifier.simproc (the_context ())
    "add_ac_proc" ["x + y::'a::ab_semigroup_add"] solve_add_ac;
end;

val eq_reflection = @{thm eq_reflection};
  
val T = @{typ "'a::ab_group_add"};

val cancel_ss = HOL_basic_ss settermless termless_agrp
  addsimprocs [add_ac_proc] addsimps
  [@{thm add_0_left}, @{thm add_0_right}, @{thm diff_def},
   @{thm minus_add_distrib}, @{thm minus_minus}, @{thm minus_zero},
   @{thm right_minus}, @{thm left_minus}, @{thm add_minus_cancel},
   @{thm minus_add_cancel}];

val sum_pats = [@{cterm "x + y::'a::ab_group_add"}, @{cterm "x - y::'a::ab_group_add"}];
  
val eqI_rules = [@{thm less_eqI}, @{thm le_eqI}, @{thm eq_eqI}];

val dest_eqI = 
  fst o HOLogic.dest_bin "op =" HOLogic.boolT o HOLogic.dest_Trueprop o concl_of;

);
*}

ML {*
  Addsimprocs [ab_group_add_cancel.sum_conv, ab_group_add_cancel.rel_conv];
*}

end