Theory Lattice_Algebras

(*  Author:     Steven Obua, TU Muenchen *)

section ‹Various algebraic structures combined with a lattice›

theory Lattice_Algebras
  imports Complex_Main
begin

class semilattice_inf_ab_group_add = ordered_ab_group_add + semilattice_inf
begin

lemma add_inf_distrib_left: "a + inf b c = inf (a + b) (a + c)" (is "?L=?R")
proof (intro order.antisym)
  show "?R ≤ ?L"
  by (metis add_commute diff_le_eq inf_greatest inf_le1 inf_le2)
qed simp

lemma add_inf_distrib_right: "inf a b + c = inf (a + c) (b + c)"
  using add_commute add_inf_distrib_left by presburger

end

class semilattice_sup_ab_group_add = ordered_ab_group_add + semilattice_sup
begin

lemma add_sup_distrib_left: "a + sup b c = sup (a + b) (a + c)" (is "?L = ?R")
proof (rule order.antisym)
  show "?L ≤ ?R"
    by (metis add_commute le_diff_eq sup.bounded_iff sup_ge1 sup_ge2)
qed simp

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)
  then show ?thesis
    by (simp add: add.commute)
qed

end

class lattice_ab_group_add = ordered_ab_group_add + lattice
begin

subclass semilattice_inf_ab_group_add ..
subclass semilattice_sup_ab_group_add ..

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 c :: 'a
  show "- sup (- a) (- b) ≤ a"
    by (rule add_le_imp_le_right [of _ "sup (uminus a) (uminus b)"])
      (simp, simp add: add_sup_distrib_left)
  show "- sup (-a) (-b) ≤ b"
    by (rule add_le_imp_le_right [of _ "sup (uminus a) (uminus b)"])
      (simp, simp add: add_sup_distrib_left)
  assume "a ≤ b" "a ≤ c"
  then show "a ≤ - 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 c :: 'a
  show "a ≤ - inf (- a) (- b)"
    by (rule add_le_imp_le_right [of _ "inf (uminus a) (uminus b)"])
      (simp, simp add: add_inf_distrib_left)
  show "b ≤ - inf (- a) (- b)"
    by (rule add_le_imp_le_right [of _ "inf (uminus a) (uminus b)"])
      (simp, simp add: add_inf_distrib_left)
  show "- inf (- a) (- b) ≤ c" if "a ≤ c" "b ≤ c"
    using that 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 diff_inf_eq_sup: "a - inf b c = a + sup (- b) (- c)"
  using neg_inf_eq_sup [of b c, symmetric] by simp

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

lemma diff_sup_eq_inf: "a - sup b c = a + inf (- b) (- c)"
  using neg_sup_eq_inf [of b c, symmetric] by simp

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)
  then have "0 = sup 0 (b - a) + inf (a - b) 0"
    by (simp add: inf_eq_neg_sup)
  then have "0 = (- a + sup a b) + (inf a b + (- b))"
    by (simp only: add_sup_distrib_left add_inf_distrib_right) simp
  then show ?thesis
    by (simp add: algebra_simps)
qed


subsection ‹Positive Part, Negative Part, Absolute Value›

definition nprt :: "'a ⇒ 'a"
  where "nprt x = inf x 0"

definition pprt :: "'a ⇒ 'a"
  where "pprt x = sup x 0"

lemma pprt_neg: "pprt (- x) = - nprt x"
proof -
  have "sup (- x) 0 = sup (- x) (- 0)"
    by (simp only: minus_zero)
  also have "… = - inf x 0"
    by (simp only: neg_inf_eq_sup)
  finally have "sup (- x) 0 = - inf x 0" .
  then show ?thesis
    by (simp only: 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 flip: add_eq_inf_sup)

lemma zero_le_pprt[simp]: "0 ≤ pprt a"
  by (simp add: pprt_def)

lemma nprt_le_zero[simp]: "nprt a ≤ 0"
  by (simp add: nprt_def)

lemma le_eq_neg: "a ≤ - b ⟷ a + b ≤ 0"
  (is "?lhs = ?rhs")
proof
  assume ?lhs
  show ?rhs
    by (rule add_le_imp_le_right[of _ "uminus b" _]) (simp add: add.assoc ‹?lhs›)
next
  assume ?rhs
  show ?lhs
    by (rule add_le_imp_le_right[of _ "b" _]) (simp add: ‹?rhs›)
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, no_atp]: "0 ≤ x ⟹ pprt x = x"
  by (simp add: pprt_def sup_absorb1)

lemma nprt_eq_id [simp, no_atp]: "x ≤ 0 ⟹ nprt x = x"
  by (simp add: nprt_def inf_absorb1)

lemma pprt_eq_0 [simp, no_atp]: "x ≤ 0 ⟹ pprt x = 0"
  by (simp add: pprt_def sup_absorb2)

lemma nprt_eq_0 [simp, no_atp]: "0 ≤ x ⟹ nprt x = 0"
  by (simp add: nprt_def inf_absorb2)

lemma sup_0_imp_0:
  assumes "sup a (- a) = 0"
  shows "a = 0"
proof -
  have pos: "0 ≤ a" if "sup a (- a) = 0" for a :: 'a
  proof -
    from that have "sup a (- a) + a = a"
      by simp
    then have "sup (a + a) 0 = a"
      by (simp add: add_sup_distrib_right)
    then have "sup (a + a) 0 ≤ a"
      by simp
    then show ?thesis
      by (blast intro: order_trans inf_sup_ord)
  qed
  from assms have **: "sup (-a) (-(-a)) = 0"
    by (simp add: sup_commute)
  from pos[OF assms] pos[OF **] show "a = 0"
    by simp
qed

lemma inf_0_imp_0: "inf a (- a) = 0 ⟹ a = 0"
  by (metis local.neg_0_equal_iff_equal neg_inf_eq_sup sup_0_imp_0)

lemma inf_0_eq_0 [simp]: "inf a (- a) = 0 ⟷ a = 0"
  by (metis inf_0_imp_0 inf.idem minus_zero)

lemma sup_0_eq_0 [simp]: "sup a (- a) = 0 ⟷ a = 0"
  by (metis minus_zero sup.idem sup_0_imp_0)

lemma zero_le_double_add_iff_zero_le_single_add [simp]: "0 ≤ a + a ⟷ 0 ≤ a"
  (is "?lhs ⟷ ?rhs")
proof
  show ?rhs if ?lhs
  proof -
    from that have a: "inf (a + a) 0 = 0"
      by (simp add: inf_commute inf_absorb1)
    have "inf a 0 + inf a 0 = inf (inf (a + a) 0) a"  (is "?l = _")
      by (simp add: add_sup_inf_distribs inf_aci)
    then have "?l = 0 + inf a 0"
      by (simp add: a, simp add: inf_commute)
    then have "inf a 0 = 0"
      by (simp only: add_right_cancel)
    then show ?thesis
      unfolding le_iff_inf by (simp add: inf_commute)
  qed
  show ?lhs if ?rhs
    by (simp add: add_mono[OF that that, simplified])
qed

lemma double_zero [simp]: "a + a = 0 ⟷ a = 0"
  using add_nonneg_eq_0_iff order.eq_iff by auto

lemma zero_less_double_add_iff_zero_less_single_add [simp]: "0 < a + a ⟷ 0 < a"
  by (meson le_less_trans less_add_same_cancel2 less_le_not_le
      zero_le_double_add_iff_zero_le_single_add)

lemma double_add_le_zero_iff_single_add_le_zero [simp]: "a + a ≤ 0 ⟷ a ≤ 0"
proof -
  have "a + a ≤ 0 ⟷ 0 ≤ - (a + a)"
    by (subst le_minus_iff) simp
  moreover have "… ⟷ a ≤ 0"
    by (simp only: minus_add_distrib zero_le_double_add_iff_zero_le_single_add) simp
  ultimately show ?thesis
    by blast
qed

lemma double_add_less_zero_iff_single_less_zero [simp]: "a + a < 0 ⟷ a < 0"
proof -
  have "a + a < 0 ⟷ 0 < - (a + a)"
    by (subst less_minus_iff) simp
  moreover have "… ⟷ a < 0"
    by (simp only: minus_add_distrib zero_less_double_add_iff_zero_less_single_add) simp
  ultimately show ?thesis
    by blast
qed

declare neg_inf_eq_sup [simp]
  and neg_sup_eq_inf [simp]
  and diff_inf_eq_sup [simp]
  and diff_sup_eq_inf [simp]

lemma le_minus_self_iff: "a ≤ - a ⟷ a ≤ 0"
proof -
  from add_le_cancel_left [of "uminus a" "plus a a" zero]
  have "a ≤ - a ⟷ a + a ≤ 0"
    by (simp flip: add.assoc)
  then show ?thesis
    by simp
qed

lemma minus_le_self_iff: "- a ≤ a ⟷ 0 ≤ a"
proof -
  have "- a ≤ a ⟷ 0 ≤ a + a"
    using add_le_cancel_left [of "uminus a" zero "plus a a"]
    by (simp flip: add.assoc)
  then show ?thesis
    by simp
qed

lemma zero_le_iff_zero_nprt: "0 ≤ a ⟷ nprt a = 0"
  unfolding le_iff_inf by (simp add: nprt_def inf_commute)

lemma le_zero_iff_zero_pprt: "a ≤ 0 ⟷ pprt a = 0"
  unfolding le_iff_sup by (simp add: pprt_def sup_commute)

lemma le_zero_iff_pprt_id: "0 ≤ a ⟷ pprt a = a"
  unfolding le_iff_sup by (simp add: pprt_def sup_commute)

lemma zero_le_iff_nprt_id: "a ≤ 0 ⟷ nprt a = a"
  unfolding le_iff_inf by (simp add: nprt_def inf_commute)

lemma pprt_mono [simp, no_atp]: "a ≤ b ⟹ pprt a ≤ pprt b"
  unfolding le_iff_sup by (simp add: pprt_def sup_aci sup_assoc [symmetric, of a])

lemma nprt_mono [simp, no_atp]: "a ≤ b ⟹ nprt a ≤ nprt b"
  unfolding le_iff_inf by (simp add: 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 lattice_ab_group_add_abs = lattice_ab_group_add + abs +
  assumes abs_lattice: "¦a¦ = sup a (- a)"
begin

lemma abs_prts: "¦a¦ = pprt a - nprt a"
proof -
  have "0 ≤ ¦a¦"
  proof -
    have a: "a ≤ ¦a¦" and b: "- a ≤ ¦a¦"
      by (auto simp add: abs_lattice)
    show ?thesis
      by (rule add_mono [OF a b, simplified])
  qed
  then have "0 ≤ 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 ac_simps pprt_def nprt_def abs_lattice)
qed

subclass ordered_ab_group_add_abs
proof
  have abs_ge_zero [simp]: "0 ≤ ¦a¦" for a
  proof -
    have a: "a ≤ ¦a¦" and b: "- a ≤ ¦a¦"
      by (auto simp add: abs_lattice)
    show "0 ≤ ¦a¦"
      by (rule add_mono [OF a b, simplified])
  qed
  have abs_leI: "a ≤ b ⟹ - a ≤ b ⟹ ¦a¦ ≤ b" for a b
    by (simp add: abs_lattice le_supI)
  fix a b
  show "0 ≤ ¦a¦"
    by simp
  show "a ≤ ¦a¦"
    by (auto simp add: abs_lattice)
  show "¦-a¦ = ¦a¦"
    by (simp add: abs_lattice sup_commute)
  show "- a ≤ b ⟹ ¦a¦ ≤ b" if "a ≤ b"
    using that by (rule abs_leI)
  show "¦a + b¦ ≤ ¦a¦ + ¦b¦"
  proof -
    have g: "¦a¦ + ¦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 ac_simps)
    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
    from a d e have "¦a + b¦ ≤ sup ?m ?n"
      by (metis abs_leI)
    with g[symmetric] show ?thesis by simp
  qed
qed

end

lemma sup_eq_if:
  fixes a :: "'a::{lattice_ab_group_add,linorder}"
  shows "sup a (- a) = (if a < 0 then - a else a)"
  using add_le_cancel_right [of a a "- a", symmetric, simplified]
    and add_le_cancel_right [of "-a" a a, symmetric, simplified]
  by (auto simp: sup_max max.absorb1 max.absorb2)

lemma abs_if_lattice:
  fixes a :: "'a::{lattice_ab_group_add_abs,linorder}"
  shows "¦a¦ = (if a < 0 then - a else a)"
  by auto

lemma estimate_by_abs:
  fixes a b c :: "'a::lattice_ab_group_add_abs"
  assumes "a + b ≤ c"
  shows "a ≤ c + ¦b¦"
proof -
  from assms have "a ≤ c + (- b)"
    by (simp add: algebra_simps)
  have "- b ≤ ¦b¦"
    by (rule abs_ge_minus_self)
  then have "c + (- b) ≤ c + ¦b¦"
    by (rule add_left_mono)
  with ‹a ≤ c + (- b)› show ?thesis
    by (rule order_trans)
qed

class lattice_ring = ordered_ring + lattice_ab_group_add_abs
begin

subclass semilattice_inf_ab_group_add ..
subclass semilattice_sup_ab_group_add ..

end

lemma abs_le_mult:
  fixes a b :: "'a::lattice_ring"
  shows "¦a * b¦ ≤ ¦a¦ * ¦b¦"
proof -
  let ?x = "pprt a * pprt b - pprt a * nprt b - nprt a * pprt b + nprt a * nprt b"
  let ?y = "pprt a * pprt b + pprt a * nprt b + nprt a * pprt b + nprt a * nprt b"
  have a: "¦a¦ * ¦b¦ = ?x"
    by (simp only: abs_prts[of a] abs_prts[of b] algebra_simps)
  have bh: "u = a ⟹ v = b ⟹
            u * v = pprt a * pprt b + pprt a * nprt b +
                    nprt a * pprt b + nprt a * nprt b" for u v :: 'a
    by (metis add.commute combine_common_factor distrib_left prts)
  note b = this[OF refl[of a] refl[of b]]
  have xy: "- ?x ≤ ?y"
    apply simp
    by (meson add_increasing2 diff_le_eq neg_le_0_iff_le nprt_le_zero order.trans split_mult_pos_le zero_le_pprt)
  have yx: "?y ≤ ?x"
    apply simp
    by (metis add_decreasing2 diff_0 diff_mono diff_zero mult_nonpos_nonneg mult_right_mono_neg mult_zero_left nprt_le_zero zero_le_pprt)
  show ?thesis
  proof (rule abs_leI)
    show "a * b ≤ ¦a¦ * ¦b¦"
      by (simp only: a b yx)
    show "- (a * b) ≤ ¦a¦ * ¦b¦"
      by (metis a bh minus_le_iff xy)
  qed
qed

instance lattice_ring ⊆ ordered_ring_abs
proof
  fix a b :: "'a::lattice_ring"
  assume a: "(0 ≤ a ∨ a ≤ 0) ∧ (0 ≤ b ∨ b ≤ 0)"
  show "¦a * b¦ = ¦a¦ * ¦b¦"
  proof -
    have s: "(0 ≤ a * b) ∨ (a * b ≤ 0)"
      by (metis a split_mult_neg_le split_mult_pos_le)
    have mulprts: "a * b = (pprt a + nprt a) * (pprt b + nprt b)"
      by (simp flip: prts)
    show ?thesis
    proof (cases "0 ≤ a * b")
      case True
      then show ?thesis
        using a split_mult_neg_le by fastforce
    next
      case False
      with s have "a * b ≤ 0"
        by simp
      then show ?thesis
        using a split_mult_pos_le by fastforce
    qed
  qed
qed

lemma mult_le_prts:
  fixes a b :: "'a::lattice_ring"
  assumes "a1 ≤ a"
    and "a ≤ a2"
    and "b1 ≤ b"
    and "b ≤ b2"
  shows "a * b ≤
    pprt a2 * pprt b2 + pprt a1 * nprt b2 + nprt a2 * pprt b1 + nprt a1 * nprt b1"
proof -
  have "a * b = (pprt a + nprt a) * (pprt b + nprt b)"
    by (subst prts[symmetric])+ simp
  then have "a * b = pprt a * pprt b + pprt a * nprt b + nprt a * pprt b + nprt a * nprt b"
    by (simp add: algebra_simps)
  moreover have "pprt a * pprt b ≤ pprt a2 * pprt b2"
    by (simp_all add: assms mult_mono)
  moreover have "pprt a * nprt b ≤ pprt a1 * nprt b2"
  proof -
    have "pprt a * nprt b ≤ pprt a * nprt b2"
      by (simp add: mult_left_mono assms)
    moreover have "pprt a * nprt b2 ≤ pprt a1 * nprt b2"
      by (simp add: mult_right_mono_neg assms)
    ultimately show ?thesis
      by simp
  qed
  moreover have "nprt a * pprt b ≤ nprt a2 * pprt b1"
  proof -
    have "nprt a * pprt b ≤ nprt a2 * pprt b"
      by (simp add: mult_right_mono assms)
    moreover have "nprt a2 * pprt b ≤ nprt a2 * pprt b1"
      by (simp add: mult_left_mono_neg assms)
    ultimately show ?thesis
      by simp
  qed
  moreover have "nprt a * nprt b ≤ nprt a1 * nprt b1"
  proof -
    have "nprt a * nprt b ≤ nprt a * nprt b1"
      by (simp add: mult_left_mono_neg assms)
    moreover have "nprt a * nprt b1 ≤ nprt a1 * nprt b1"
      by (simp add: mult_right_mono_neg assms)
    ultimately show ?thesis
      by simp
  qed
  ultimately show ?thesis
    by - (rule add_mono | simp)+
qed

lemma mult_ge_prts:
  fixes a b :: "'a::lattice_ring"
  assumes "a1 ≤ a"
    and "a ≤ a2"
    and "b1 ≤ b"
    and "b ≤ b2"
  shows "a * b ≥
    nprt a1 * pprt b2 + nprt a2 * nprt b2 + pprt a1 * pprt b1 + pprt a2 * nprt b1"
proof -
  from assms have a1: "- a2 ≤ -a"
    by auto
  from assms have a2: "- a ≤ -a1"
    by auto
  from mult_le_prts[of "- a2" "- a" "- a1" "b1" b "b2",
    OF a1 a2 assms(3) assms(4), simplified nprt_neg pprt_neg]
  have le: "- (a * b) ≤
    - nprt a1 * pprt b2 + - nprt a2 * nprt b2 +
    - pprt a1 * pprt b1 + - pprt a2 * nprt b1"
    by simp
  then have "- (- nprt a1 * pprt b2 + - nprt a2 * nprt b2 +
      - pprt a1 * pprt b1 + - pprt a2 * nprt b1) ≤ a * b"
    by (simp only: minus_le_iff)
  then show ?thesis
    by (simp add: algebra_simps)
qed

instance int :: lattice_ring
proof
  show "¦k¦ = sup k (- k)" for k :: int
    by (auto simp add: sup_int_def)
qed

instance real :: lattice_ring
proof
  show "¦a¦ = sup a (- a)" for a :: real
    by (auto simp add: sup_real_def)
qed

end