# Theory Real

theory Real
imports Rat
```(*  Title:      HOL/Real.thy
Author:     Jacques D. Fleuriot, University of Edinburgh, 1998
Author:     Larry Paulson, University of Cambridge
Author:     Jeremy Avigad, Carnegie Mellon University
Author:     Florian Zuleger, Johannes Hoelzl, and Simon Funke, TU Muenchen
Conversion to Isar and new proofs by Lawrence C Paulson, 2003/4
Construction of Cauchy Reals by Brian Huffman, 2010
*)

section ‹Development of the Reals using Cauchy Sequences›

theory Real
imports Rat
begin

text ‹
This theory contains a formalization of the real numbers as equivalence
classes of Cauchy sequences of rationals. See
🗏‹~~/src/HOL/ex/Dedekind_Real.thy› for an alternative construction using
Dedekind cuts.
›

subsection ‹Preliminary lemmas›

text‹Useful in convergence arguments›
lemma inverse_of_nat_le:
fixes n::nat shows "⟦n ≤ m; n≠0⟧ ⟹ 1 / of_nat m ≤ (1::'a::linordered_field) / of_nat n"

lemma inj_add_left [simp]: "inj ((+) x)"

lemma inj_mult_left [simp]: "inj (( * ) x) ⟷ x ≠ 0"
for x :: "'a::idom"
by (metis injI mult_cancel_left the_inv_f_f zero_neq_one)

lemma add_diff_add: "(a + c) - (b + d) = (a - b) + (c - d)"
for a b c d :: "'a::ab_group_add"
by simp

lemma minus_diff_minus: "- a - - b = - (a - b)"
by simp

lemma mult_diff_mult: "(x * y - a * b) = x * (y - b) + (x - a) * b"
for x y a b :: "'a::ring"

lemma inverse_diff_inverse:
fixes a b :: "'a::division_ring"
assumes "a ≠ 0" and "b ≠ 0"
shows "inverse a - inverse b = - (inverse a * (a - b) * inverse b)"
using assms by (simp add: algebra_simps)

lemma obtain_pos_sum:
fixes r :: rat assumes r: "0 < r"
obtains s t where "0 < s" and "0 < t" and "r = s + t"
proof
from r show "0 < r/2" by simp
from r show "0 < r/2" by simp
show "r = r/2 + r/2" by simp
qed

subsection ‹Sequences that converge to zero›

definition vanishes :: "(nat ⇒ rat) ⇒ bool"
where "vanishes X ⟷ (∀r>0. ∃k. ∀n≥k. ¦X n¦ < r)"

lemma vanishesI: "(⋀r. 0 < r ⟹ ∃k. ∀n≥k. ¦X n¦ < r) ⟹ vanishes X"
unfolding vanishes_def by simp

lemma vanishesD: "vanishes X ⟹ 0 < r ⟹ ∃k. ∀n≥k. ¦X n¦ < r"
unfolding vanishes_def by simp

lemma vanishes_const [simp]: "vanishes (λn. c) ⟷ c = 0"
proof (cases "c = 0")
case True
then show ?thesis
next
case False
then show ?thesis
unfolding vanishes_def
using zero_less_abs_iff by blast
qed

lemma vanishes_minus: "vanishes X ⟹ vanishes (λn. - X n)"
unfolding vanishes_def by simp

assumes X: "vanishes X"
and Y: "vanishes Y"
shows "vanishes (λn. X n + Y n)"
proof (rule vanishesI)
fix r :: rat
assume "0 < r"
then obtain s t where s: "0 < s" and t: "0 < t" and r: "r = s + t"
by (rule obtain_pos_sum)
obtain i where i: "∀n≥i. ¦X n¦ < s"
using vanishesD [OF X s] ..
obtain j where j: "∀n≥j. ¦Y n¦ < t"
using vanishesD [OF Y t] ..
have "∀n≥max i j. ¦X n + Y n¦ < r"
proof clarsimp
fix n
assume n: "i ≤ n" "j ≤ n"
have "¦X n + Y n¦ ≤ ¦X n¦ + ¦Y n¦"
by (rule abs_triangle_ineq)
also have "… < s + t"
finally show "¦X n + Y n¦ < r"
by (simp only: r)
qed
then show "∃k. ∀n≥k. ¦X n + Y n¦ < r" ..
qed

lemma vanishes_diff:
assumes "vanishes X" "vanishes Y"
shows "vanishes (λn. X n - Y n)"

lemma vanishes_mult_bounded:
assumes X: "∃a>0. ∀n. ¦X n¦ < a"
assumes Y: "vanishes (λn. Y n)"
shows "vanishes (λn. X n * Y n)"
proof (rule vanishesI)
fix r :: rat
assume r: "0 < r"
obtain a where a: "0 < a" "∀n. ¦X n¦ < a"
using X by blast
obtain b where b: "0 < b" "r = a * b"
proof
show "0 < r / a" using r a by simp
show "r = a * (r / a)" using a by simp
qed
obtain k where k: "∀n≥k. ¦Y n¦ < b"
using vanishesD [OF Y b(1)] ..
have "∀n≥k. ¦X n * Y n¦ < r"
by (simp add: b(2) abs_mult mult_strict_mono' a k)
then show "∃k. ∀n≥k. ¦X n * Y n¦ < r" ..
qed

subsection ‹Cauchy sequences›

definition cauchy :: "(nat ⇒ rat) ⇒ bool"
where "cauchy X ⟷ (∀r>0. ∃k. ∀m≥k. ∀n≥k. ¦X m - X n¦ < r)"

lemma cauchyI: "(⋀r. 0 < r ⟹ ∃k. ∀m≥k. ∀n≥k. ¦X m - X n¦ < r) ⟹ cauchy X"
unfolding cauchy_def by simp

lemma cauchyD: "cauchy X ⟹ 0 < r ⟹ ∃k. ∀m≥k. ∀n≥k. ¦X m - X n¦ < r"
unfolding cauchy_def by simp

lemma cauchy_const [simp]: "cauchy (λn. x)"
unfolding cauchy_def by simp

assumes X: "cauchy X" and Y: "cauchy Y"
shows "cauchy (λn. X n + Y n)"
proof (rule cauchyI)
fix r :: rat
assume "0 < r"
then obtain s t where s: "0 < s" and t: "0 < t" and r: "r = s + t"
by (rule obtain_pos_sum)
obtain i where i: "∀m≥i. ∀n≥i. ¦X m - X n¦ < s"
using cauchyD [OF X s] ..
obtain j where j: "∀m≥j. ∀n≥j. ¦Y m - Y n¦ < t"
using cauchyD [OF Y t] ..
have "∀m≥max i j. ∀n≥max i j. ¦(X m + Y m) - (X n + Y n)¦ < r"
proof clarsimp
fix m n
assume *: "i ≤ m" "j ≤ m" "i ≤ n" "j ≤ n"
have "¦(X m + Y m) - (X n + Y n)¦ ≤ ¦X m - X n¦ + ¦Y m - Y n¦"
also have "… < s + t"
finally show "¦(X m + Y m) - (X n + Y n)¦ < r" by (simp only: r)
qed
then show "∃k. ∀m≥k. ∀n≥k. ¦(X m + Y m) - (X n + Y n)¦ < r" ..
qed

lemma cauchy_minus [simp]:
assumes X: "cauchy X"
shows "cauchy (λn. - X n)"
using assms unfolding cauchy_def
unfolding minus_diff_minus abs_minus_cancel .

lemma cauchy_diff [simp]:
assumes "cauchy X" "cauchy Y"
shows "cauchy (λn. X n - Y n)"

lemma cauchy_imp_bounded:
assumes "cauchy X"
shows "∃b>0. ∀n. ¦X n¦ < b"
proof -
obtain k where k: "∀m≥k. ∀n≥k. ¦X m - X n¦ < 1"
using cauchyD [OF assms zero_less_one] ..
show "∃b>0. ∀n. ¦X n¦ < b"
proof (intro exI conjI allI)
have "0 ≤ ¦X 0¦" by simp
also have "¦X 0¦ ≤ Max (abs ` X ` {..k})" by simp
finally have "0 ≤ Max (abs ` X ` {..k})" .
then show "0 < Max (abs ` X ` {..k}) + 1" by simp
next
fix n :: nat
show "¦X n¦ < Max (abs ` X ` {..k}) + 1"
proof (rule linorder_le_cases)
assume "n ≤ k"
then have "¦X n¦ ≤ Max (abs ` X ` {..k})" by simp
then show "¦X n¦ < Max (abs ` X ` {..k}) + 1" by simp
next
assume "k ≤ n"
have "¦X n¦ = ¦X k + (X n - X k)¦" by simp
also have "¦X k + (X n - X k)¦ ≤ ¦X k¦ + ¦X n - X k¦"
by (rule abs_triangle_ineq)
also have "… < Max (abs ` X ` {..k}) + 1"
finally show "¦X n¦ < Max (abs ` X ` {..k}) + 1" .
qed
qed
qed

lemma cauchy_mult [simp]:
assumes X: "cauchy X" and Y: "cauchy Y"
shows "cauchy (λn. X n * Y n)"
proof (rule cauchyI)
fix r :: rat assume "0 < r"
then obtain u v where u: "0 < u" and v: "0 < v" and "r = u + v"
by (rule obtain_pos_sum)
obtain a where a: "0 < a" "∀n. ¦X n¦ < a"
using cauchy_imp_bounded [OF X] by blast
obtain b where b: "0 < b" "∀n. ¦Y n¦ < b"
using cauchy_imp_bounded [OF Y] by blast
obtain s t where s: "0 < s" and t: "0 < t" and r: "r = a * t + s * b"
proof
show "0 < v/b" using v b(1) by simp
show "0 < u/a" using u a(1) by simp
show "r = a * (u/a) + (v/b) * b"
using a(1) b(1) ‹r = u + v› by simp
qed
obtain i where i: "∀m≥i. ∀n≥i. ¦X m - X n¦ < s"
using cauchyD [OF X s] ..
obtain j where j: "∀m≥j. ∀n≥j. ¦Y m - Y n¦ < t"
using cauchyD [OF Y t] ..
have "∀m≥max i j. ∀n≥max i j. ¦X m * Y m - X n * Y n¦ < r"
proof clarsimp
fix m n
assume *: "i ≤ m" "j ≤ m" "i ≤ n" "j ≤ n"
have "¦X m * Y m - X n * Y n¦ = ¦X m * (Y m - Y n) + (X m - X n) * Y n¦"
unfolding mult_diff_mult ..
also have "… ≤ ¦X m * (Y m - Y n)¦ + ¦(X m - X n) * Y n¦"
by (rule abs_triangle_ineq)
also have "… = ¦X m¦ * ¦Y m - Y n¦ + ¦X m - X n¦ * ¦Y n¦"
unfolding abs_mult ..
also have "… < a * t + s * b"
finally show "¦X m * Y m - X n * Y n¦ < r"
by (simp only: r)
qed
then show "∃k. ∀m≥k. ∀n≥k. ¦X m * Y m - X n * Y n¦ < r" ..
qed

lemma cauchy_not_vanishes_cases:
assumes X: "cauchy X"
assumes nz: "¬ vanishes X"
shows "∃b>0. ∃k. (∀n≥k. b < - X n) ∨ (∀n≥k. b < X n)"
proof -
obtain r where "0 < r" and r: "∀k. ∃n≥k. r ≤ ¦X n¦"
using nz unfolding vanishes_def by (auto simp add: not_less)
obtain s t where s: "0 < s" and t: "0 < t" and "r = s + t"
using ‹0 < r› by (rule obtain_pos_sum)
obtain i where i: "∀m≥i. ∀n≥i. ¦X m - X n¦ < s"
using cauchyD [OF X s] ..
obtain k where "i ≤ k" and "r ≤ ¦X k¦"
using r by blast
have k: "∀n≥k. ¦X n - X k¦ < s"
using i ‹i ≤ k› by auto
have "X k ≤ - r ∨ r ≤ X k"
using ‹r ≤ ¦X k¦› by auto
then have "(∀n≥k. t < - X n) ∨ (∀n≥k. t < X n)"
unfolding ‹r = s + t› using k by auto
then have "∃k. (∀n≥k. t < - X n) ∨ (∀n≥k. t < X n)" ..
then show "∃t>0. ∃k. (∀n≥k. t < - X n) ∨ (∀n≥k. t < X n)"
using t by auto
qed

lemma cauchy_not_vanishes:
assumes X: "cauchy X"
and nz: "¬ vanishes X"
shows "∃b>0. ∃k. ∀n≥k. b < ¦X n¦"
using cauchy_not_vanishes_cases [OF assms]
by (elim ex_forward conj_forward asm_rl) auto

lemma cauchy_inverse [simp]:
assumes X: "cauchy X"
and nz: "¬ vanishes X"
shows "cauchy (λn. inverse (X n))"
proof (rule cauchyI)
fix r :: rat
assume "0 < r"
obtain b i where b: "0 < b" and i: "∀n≥i. b < ¦X n¦"
using cauchy_not_vanishes [OF X nz] by blast
from b i have nz: "∀n≥i. X n ≠ 0" by auto
obtain s where s: "0 < s" and r: "r = inverse b * s * inverse b"
proof
show "0 < b * r * b" by (simp add: ‹0 < r› b)
show "r = inverse b * (b * r * b) * inverse b"
using b by simp
qed
obtain j where j: "∀m≥j. ∀n≥j. ¦X m - X n¦ < s"
using cauchyD [OF X s] ..
have "∀m≥max i j. ∀n≥max i j. ¦inverse (X m) - inverse (X n)¦ < r"
proof clarsimp
fix m n
assume *: "i ≤ m" "j ≤ m" "i ≤ n" "j ≤ n"
have "¦inverse (X m) - inverse (X n)¦ = inverse ¦X m¦ * ¦X m - X n¦ * inverse ¦X n¦"
by (simp add: inverse_diff_inverse nz * abs_mult)
also have "… < inverse b * s * inverse b"
by (simp add: mult_strict_mono less_imp_inverse_less i j b * s)
finally show "¦inverse (X m) - inverse (X n)¦ < r" by (simp only: r)
qed
then show "∃k. ∀m≥k. ∀n≥k. ¦inverse (X m) - inverse (X n)¦ < r" ..
qed

lemma vanishes_diff_inverse:
assumes X: "cauchy X" "¬ vanishes X"
and Y: "cauchy Y" "¬ vanishes Y"
and XY: "vanishes (λn. X n - Y n)"
shows "vanishes (λn. inverse (X n) - inverse (Y n))"
proof (rule vanishesI)
fix r :: rat
assume r: "0 < r"
obtain a i where a: "0 < a" and i: "∀n≥i. a < ¦X n¦"
using cauchy_not_vanishes [OF X] by blast
obtain b j where b: "0 < b" and j: "∀n≥j. b < ¦Y n¦"
using cauchy_not_vanishes [OF Y] by blast
obtain s where s: "0 < s" and "inverse a * s * inverse b = r"
proof
show "0 < a * r * b"
using a r b by simp
show "inverse a * (a * r * b) * inverse b = r"
using a r b by simp
qed
obtain k where k: "∀n≥k. ¦X n - Y n¦ < s"
using vanishesD [OF XY s] ..
have "∀n≥max (max i j) k. ¦inverse (X n) - inverse (Y n)¦ < r"
proof clarsimp
fix n
assume n: "i ≤ n" "j ≤ n" "k ≤ n"
with i j a b have "X n ≠ 0" and "Y n ≠ 0"
by auto
then have "¦inverse (X n) - inverse (Y n)¦ = inverse ¦X n¦ * ¦X n - Y n¦ * inverse ¦Y n¦"
also have "… < inverse a * s * inverse b"
by (intro mult_strict_mono' less_imp_inverse_less) (simp_all add: a b i j k n)
also note ‹inverse a * s * inverse b = r›
finally show "¦inverse (X n) - inverse (Y n)¦ < r" .
qed
then show "∃k. ∀n≥k. ¦inverse (X n) - inverse (Y n)¦ < r" ..
qed

subsection ‹Equivalence relation on Cauchy sequences›

definition realrel :: "(nat ⇒ rat) ⇒ (nat ⇒ rat) ⇒ bool"
where "realrel = (λX Y. cauchy X ∧ cauchy Y ∧ vanishes (λn. X n - Y n))"

lemma realrelI [intro?]: "cauchy X ⟹ cauchy Y ⟹ vanishes (λn. X n - Y n) ⟹ realrel X Y"

lemma realrel_refl: "cauchy X ⟹ realrel X X"

lemma symp_realrel: "symp realrel"
by (simp add: abs_minus_commute realrel_def symp_def vanishes_def)

lemma transp_realrel: "transp realrel"
unfolding realrel_def

lemma part_equivp_realrel: "part_equivp realrel"
by (blast intro: part_equivpI symp_realrel transp_realrel realrel_refl cauchy_const)

subsection ‹The field of real numbers›

quotient_type real = "nat ⇒ rat" / partial: realrel
morphisms rep_real Real
by (rule part_equivp_realrel)

lemma cr_real_eq: "pcr_real = (λx y. cauchy x ∧ Real x = y)"
unfolding real.pcr_cr_eq cr_real_def realrel_def by auto

lemma Real_induct [induct type: real]: (* TODO: generate automatically *)
assumes "⋀X. cauchy X ⟹ P (Real X)"
shows "P x"
proof (induct x)
case (1 X)
then have "cauchy X" by (simp add: realrel_def)
then show "P (Real X)" by (rule assms)
qed

lemma eq_Real: "cauchy X ⟹ cauchy Y ⟹ Real X = Real Y ⟷ vanishes (λn. X n - Y n)"
using real.rel_eq_transfer
unfolding real.pcr_cr_eq cr_real_def rel_fun_def realrel_def by simp

lemma Domainp_pcr_real [transfer_domain_rule]: "Domainp pcr_real = cauchy"

instantiation real :: field
begin

lift_definition zero_real :: "real" is "λn. 0"

lift_definition one_real :: "real" is "λn. 1"

lift_definition plus_real :: "real ⇒ real ⇒ real" is "λX Y n. X n + Y n"

lift_definition uminus_real :: "real ⇒ real" is "λX n. - X n"
unfolding realrel_def minus_diff_minus
by (simp only: cauchy_minus vanishes_minus simp_thms)

lift_definition times_real :: "real ⇒ real ⇒ real" is "λX Y n. X n * Y n"
proof -
fix f1 f2 f3 f4
have "⟦cauchy f1; cauchy f4; vanishes (λn. f1 n - f2 n); vanishes (λn. f3 n - f4 n)⟧
⟹ vanishes (λn. f1 n * (f3 n - f4 n) + f4 n * (f1 n - f2 n))"
then show "⟦realrel f1 f2; realrel f3 f4⟧ ⟹ realrel (λn. f1 n * f3 n) (λn. f2 n * f4 n)"
by (simp add: mult.commute realrel_def mult_diff_mult)
qed

lift_definition inverse_real :: "real ⇒ real"
is "λX. if vanishes X then (λn. 0) else (λn. inverse (X n))"
proof -
fix X Y
assume "realrel X Y"
then have X: "cauchy X" and Y: "cauchy Y" and XY: "vanishes (λn. X n - Y n)"
have "vanishes X ⟷ vanishes Y"
proof
assume "vanishes X"
from vanishes_diff [OF this XY] show "vanishes Y"
by simp
next
assume "vanishes Y"
from vanishes_add [OF this XY] show "vanishes X"
by simp
qed
then show "?thesis X Y"
by (simp add: vanishes_diff_inverse X Y XY realrel_def)
qed

definition "x - y = x + - y" for x y :: real

definition "x div y = x * inverse y" for x y :: real

lemma add_Real: "cauchy X ⟹ cauchy Y ⟹ Real X + Real Y = Real (λn. X n + Y n)"
using plus_real.transfer by (simp add: cr_real_eq rel_fun_def)

lemma minus_Real: "cauchy X ⟹ - Real X = Real (λn. - X n)"
using uminus_real.transfer by (simp add: cr_real_eq rel_fun_def)

lemma diff_Real: "cauchy X ⟹ cauchy Y ⟹ Real X - Real Y = Real (λn. X n - Y n)"

lemma mult_Real: "cauchy X ⟹ cauchy Y ⟹ Real X * Real Y = Real (λn. X n * Y n)"
using times_real.transfer by (simp add: cr_real_eq rel_fun_def)

lemma inverse_Real:
"cauchy X ⟹ inverse (Real X) = (if vanishes X then 0 else Real (λn. inverse (X n)))"
using inverse_real.transfer zero_real.transfer
unfolding cr_real_eq rel_fun_def by (simp split: if_split_asm, metis)

instance
proof
fix a b c :: real
show "a + b = b + a"
by transfer (simp add: ac_simps realrel_def)
show "(a + b) + c = a + (b + c)"
by transfer (simp add: ac_simps realrel_def)
show "0 + a = a"
show "- a + a = 0"
show "a - b = a + - b"
by (rule minus_real_def)
show "(a * b) * c = a * (b * c)"
by transfer (simp add: ac_simps realrel_def)
show "a * b = b * a"
by transfer (simp add: ac_simps realrel_def)
show "1 * a = a"
by transfer (simp add: ac_simps realrel_def)
show "(a + b) * c = a * c + b * c"
by transfer (simp add: distrib_right realrel_def)
show "(0::real) ≠ (1::real)"
have "vanishes (λn. inverse (X n) * X n - 1)" if X: "cauchy X" "¬ vanishes X" for X
proof (rule vanishesI)
fix r::rat
assume "0 < r"
obtain b k where "b>0" "∀n≥k. b < ¦X n¦"
using X cauchy_not_vanishes by blast
then show "∃k. ∀n≥k. ¦inverse (X n) * X n - 1¦ < r"
using ‹0 < r› by force
qed
then show "a ≠ 0 ⟹ inverse a * a = 1"
show "a div b = a * inverse b"
by (rule divide_real_def)
show "inverse (0::real) = 0"
qed

end

subsection ‹Positive reals›

lift_definition positive :: "real ⇒ bool"
is "λX. ∃r>0. ∃k. ∀n≥k. r < X n"
proof -
have 1: "∃r>0. ∃k. ∀n≥k. r < Y n"
if *: "realrel X Y" and **: "∃r>0. ∃k. ∀n≥k. r < X n" for X Y
proof -
from * have XY: "vanishes (λn. X n - Y n)"
from ** obtain r i where "0 < r" and i: "∀n≥i. r < X n"
by blast
obtain s t where s: "0 < s" and t: "0 < t" and r: "r = s + t"
using ‹0 < r› by (rule obtain_pos_sum)
obtain j where j: "∀n≥j. ¦X n - Y n¦ < s"
using vanishesD [OF XY s] ..
have "∀n≥max i j. t < Y n"
proof clarsimp
fix n
assume n: "i ≤ n" "j ≤ n"
have "¦X n - Y n¦ < s" and "r < X n"
using i j n by simp_all
then show "t < Y n" by (simp add: r)
qed
then show ?thesis using t by blast
qed
fix X Y assume "realrel X Y"
then have "realrel X Y" and "realrel Y X"
using symp_realrel by (auto simp: symp_def)
then show "?thesis X Y"
by (safe elim!: 1)
qed

lemma positive_Real: "cauchy X ⟹ positive (Real X) ⟷ (∃r>0. ∃k. ∀n≥k. r < X n)"
using positive.transfer by (simp add: cr_real_eq rel_fun_def)

lemma positive_zero: "¬ positive 0"
by transfer auto

assumes "positive x" "positive y" shows "positive (x + y)"
proof -
have *: "⟦∀n≥i. a < x n; ∀n≥j. b < y n; 0 < a; 0 < b; n ≥ max i j⟧
⟹ a+b < x n + y n" for x y and a b::rat and i j n::nat
show ?thesis
using assms
by transfer (blast intro: * pos_add_strict)
qed

lemma positive_mult:
assumes "positive x" "positive y" shows "positive (x * y)"
proof -
have *: "⟦∀n≥i. a < x n; ∀n≥j. b < y n; 0 < a; 0 < b; n ≥ max i j⟧
⟹ a*b < x n * y n" for x y and a b::rat and i j n::nat
show ?thesis
using assms
by transfer (blast intro: *  mult_pos_pos)
qed

lemma positive_minus: "¬ positive x ⟹ x ≠ 0 ⟹ positive (- x)"
apply transfer
apply (blast dest: cauchy_not_vanishes_cases)
done

instantiation real :: linordered_field
begin

definition "x < y ⟷ positive (y - x)"

definition "x ≤ y ⟷ x < y ∨ x = y" for x y :: real

definition "¦a¦ = (if a < 0 then - a else a)" for a :: real

definition "sgn a = (if a = 0 then 0 else if 0 < a then 1 else - 1)" for a :: real

instance
proof
fix a b c :: real
show "¦a¦ = (if a < 0 then - a else a)"
by (rule abs_real_def)
show "a < b ⟷ a ≤ b ∧ ¬ b ≤ a"
"a ≤ b ⟹ b ≤ c ⟹ a ≤ c"  "a ≤ a"
"a ≤ b ⟹ b ≤ a ⟹ a = b"
"a ≤ b ⟹ c + a ≤ c + b"
unfolding less_eq_real_def less_real_def
show "sgn a = (if a = 0 then 0 else if 0 < a then 1 else - 1)"
by (rule sgn_real_def)
show "a ≤ b ∨ b ≤ a"
by (auto dest!: positive_minus simp: less_eq_real_def less_real_def)
show "a < b ⟹ 0 < c ⟹ c * a < c * b"
unfolding less_real_def
by (force simp add: algebra_simps dest: positive_mult)
qed

end

instantiation real :: distrib_lattice
begin

definition "(inf :: real ⇒ real ⇒ real) = min"

definition "(sup :: real ⇒ real ⇒ real) = max"

instance
by standard (auto simp add: inf_real_def sup_real_def max_min_distrib2)

end

lemma of_nat_Real: "of_nat x = Real (λn. of_nat x)"

lemma of_int_Real: "of_int x = Real (λn. of_int x)"
by (cases x rule: int_diff_cases) (simp add: of_nat_Real diff_Real)

lemma of_rat_Real: "of_rat x = Real (λn. x)"
proof (induct x)
case (Fract a b)
then show ?case
apply (simp add: of_int_Real divide_inverse inverse_Real mult_Real)
done
qed

instance real :: archimedean_field
proof
show "∃z. x ≤ of_int z" for x :: real
proof (induct x)
case (1 X)
then obtain b where "0 < b" and b: "⋀n. ¦X n¦ < b"
by (blast dest: cauchy_imp_bounded)
then have "Real X < of_int (⌈b⌉ + 1)"
using 1
apply (simp add: of_int_Real less_real_def diff_Real positive_Real)
apply (rule_tac x=1 in exI)
by (metis abs_ge_self le_less_trans le_of_int_ceiling less_le)
then show ?case
using less_eq_real_def by blast
qed
qed

instantiation real :: floor_ceiling
begin

definition [code del]: "⌊x::real⌋ = (THE z. of_int z ≤ x ∧ x < of_int (z + 1))"

instance
proof
show "of_int ⌊x⌋ ≤ x ∧ x < of_int (⌊x⌋ + 1)" for x :: real
unfolding floor_real_def using floor_exists1 by (rule theI')
qed

end

subsection ‹Completeness›

lemma not_positive_Real:
assumes "cauchy X" shows "¬ positive (Real X) ⟷ (∀r>0. ∃k. ∀n≥k. X n ≤ r)" (is "?lhs = ?rhs")
unfolding positive_Real [OF assms]
proof (intro iffI allI notI impI)
show "∃k. ∀n≥k. X n ≤ r" if r: "¬ (∃r>0. ∃k. ∀n≥k. r < X n)" and "0 < r" for r
proof -
obtain s t where "s > 0" "t > 0" "r = s+t"
using ‹r > 0› obtain_pos_sum by blast
obtain k where k: "⋀m n. ⟦m≥k; n≥k⟧ ⟹ ¦X m - X n¦ < t"
using cauchyD [OF assms ‹t > 0›] by blast
obtain n where "n ≥ k" "X n ≤ s"
by (meson r ‹0 < s› not_less)
then have "X l ≤ r" if "l ≥ n" for l
using k [OF ‹n ≥ k›, of l] that ‹r = s+t› by linarith
then show ?thesis
by blast
qed
qed (meson le_cases not_le)

lemma le_Real:
assumes "cauchy X" "cauchy Y"
shows "Real X ≤ Real Y = (∀r>0. ∃k. ∀n≥k. X n ≤ Y n + r)"
unfolding not_less [symmetric, where 'a=real] less_real_def
apply (simp add: diff_Real not_positive_Real assms)
done

lemma le_RealI:
assumes Y: "cauchy Y"
shows "∀n. x ≤ of_rat (Y n) ⟹ x ≤ Real Y"
proof (induct x)
fix X
assume X: "cauchy X" and "∀n. Real X ≤ of_rat (Y n)"
then have le: "⋀m r. 0 < r ⟹ ∃k. ∀n≥k. X n ≤ Y m + r"
then have "∃k. ∀n≥k. X n ≤ Y n + r" if "0 < r" for r :: rat
proof -
from that obtain s t where s: "0 < s" and t: "0 < t" and r: "r = s + t"
by (rule obtain_pos_sum)
obtain i where i: "∀m≥i. ∀n≥i. ¦Y m - Y n¦ < s"
using cauchyD [OF Y s] ..
obtain j where j: "∀n≥j. X n ≤ Y i + t"
using le [OF t] ..
have "∀n≥max i j. X n ≤ Y n + r"
proof clarsimp
fix n
assume n: "i ≤ n" "j ≤ n"
have "X n ≤ Y i + t"
using n j by simp
moreover have "¦Y i - Y n¦ < s"
using n i by simp
ultimately show "X n ≤ Y n + r"
unfolding r by simp
qed
then show ?thesis ..
qed
then show "Real X ≤ Real Y"
by (simp add: of_rat_Real le_Real X Y)
qed

lemma Real_leI:
assumes X: "cauchy X"
assumes le: "∀n. of_rat (X n) ≤ y"
shows "Real X ≤ y"
proof -
have "- y ≤ - Real X"
by (simp add: minus_Real X le_RealI of_rat_minus le)
then show ?thesis by simp
qed

lemma less_RealD:
assumes "cauchy Y"
shows "x < Real Y ⟹ ∃n. x < of_rat (Y n)"
apply (erule contrapos_pp)
apply (erule Real_leI [OF assms])
done

lemma of_nat_less_two_power [simp]: "of_nat n < (2::'a::linordered_idom) ^ n"
apply (induct n)
apply simp
apply (metis add_le_less_mono mult_2 of_nat_Suc one_le_numeral one_le_power power_Suc)
done

lemma complete_real:
fixes S :: "real set"
assumes "∃x. x ∈ S" and "∃z. ∀x∈S. x ≤ z"
shows "∃y. (∀x∈S. x ≤ y) ∧ (∀z. (∀x∈S. x ≤ z) ⟶ y ≤ z)"
proof -
obtain x where x: "x ∈ S" using assms(1) ..
obtain z where z: "∀x∈S. x ≤ z" using assms(2) ..

define P where "P x ⟷ (∀y∈S. y ≤ of_rat x)" for x
obtain a where a: "¬ P a"
proof
have "of_int ⌊x - 1⌋ ≤ x - 1" by (rule of_int_floor_le)
also have "x - 1 < x" by simp
finally have "of_int ⌊x - 1⌋ < x" .
then have "¬ x ≤ of_int ⌊x - 1⌋" by (simp only: not_le)
then show "¬ P (of_int ⌊x - 1⌋)"
unfolding P_def of_rat_of_int_eq using x by blast
qed
obtain b where b: "P b"
proof
show "P (of_int ⌈z⌉)"
unfolding P_def of_rat_of_int_eq
proof
fix y assume "y ∈ S"
then have "y ≤ z" using z by simp
also have "z ≤ of_int ⌈z⌉" by (rule le_of_int_ceiling)
finally show "y ≤ of_int ⌈z⌉" .
qed
qed

define avg where "avg x y = x/2 + y/2" for x y :: rat
define bisect where "bisect = (λ(x, y). if P (avg x y) then (x, avg x y) else (avg x y, y))"
define A where "A n = fst ((bisect ^^ n) (a, b))" for n
define B where "B n = snd ((bisect ^^ n) (a, b))" for n
define C where "C n = avg (A n) (B n)" for n
have A_0 [simp]: "A 0 = a" unfolding A_def by simp
have B_0 [simp]: "B 0 = b" unfolding B_def by simp
have A_Suc [simp]: "⋀n. A (Suc n) = (if P (C n) then A n else C n)"
unfolding A_def B_def C_def bisect_def split_def by simp
have B_Suc [simp]: "⋀n. B (Suc n) = (if P (C n) then C n else B n)"
unfolding A_def B_def C_def bisect_def split_def by simp

have width: "B n - A n = (b - a) / 2^n" for n
proof (induct n)
case (Suc n)
then show ?case
by (simp add: C_def eq_divide_eq avg_def algebra_simps)
qed simp
have twos: "∃n. y / 2 ^ n < r" if "0 < r" for y r :: rat
proof -
obtain n where "y / r < rat_of_nat n"
using ‹0 < r› reals_Archimedean2 by blast
then have "∃n. y < r * 2 ^ n"
by (metis divide_less_eq less_trans mult.commute of_nat_less_two_power that)
then show ?thesis
qed
have PA: "¬ P (A n)" for n
by (induct n) (simp_all add: a)
have PB: "P (B n)" for n
by (induct n) (simp_all add: b)
have ab: "a < b"
using a b unfolding P_def
by (meson leI less_le_trans of_rat_less)
have AB: "A n < B n" for n
by (induct n) (simp_all add: ab C_def avg_def)
have  "A i ≤ A j ∧  B j ≤ B i" if "i < j" for i j
using that
proof (induction rule: less_Suc_induct)
case (1 i)
then show ?case
apply (rule AB [THEN less_imp_le])
done
qed simp
then have A_mono: "A i ≤ A j" and B_mono: "B j ≤ B i" if "i ≤ j" for i j
by (metis eq_refl le_neq_implies_less that)+
have cauchy_lemma: "cauchy X" if *: "⋀n i. i≥n ⟹ A n ≤ X i ∧ X i ≤ B n" for X
proof (rule cauchyI)
fix r::rat
assume "0 < r"
then obtain k where k: "(b - a) / 2 ^ k < r"
using twos by blast
have "¦X m - X n¦ < r" if "m≥k" "n≥k" for m n
proof -
have "¦X m - X n¦ ≤ B k - A k"
by (simp add: * abs_rat_def diff_mono that)
also have "... < r"
finally show ?thesis .
qed
then show "∃k. ∀m≥k. ∀n≥k. ¦X m - X n¦ < r"
by blast
qed
have "cauchy A"
by (rule cauchy_lemma) (meson AB A_mono B_mono dual_order.strict_implies_order less_le_trans)
have "cauchy B"
by (rule cauchy_lemma) (meson AB A_mono B_mono dual_order.strict_implies_order le_less_trans)
have "∀x∈S. x ≤ Real B"
proof
fix x
assume "x ∈ S"
then show "x ≤ Real B"
using PB [unfolded P_def] ‹cauchy B›
qed
moreover have "∀z. (∀x∈S. x ≤ z) ⟶ Real A ≤ z"
by (meson PA Real_leI P_def ‹cauchy A› le_cases order.trans)
moreover have "vanishes (λn. (b - a) / 2 ^ n)"
proof (rule vanishesI)
fix r :: rat
assume "0 < r"
then obtain k where k: "¦b - a¦ / 2 ^ k < r"
using twos by blast
have "∀n≥k. ¦(b - a) / 2 ^ n¦ < r"
proof clarify
fix n
assume n: "k ≤ n"
have "¦(b - a) / 2 ^ n¦ = ¦b - a¦ / 2 ^ n"
by simp
also have "… ≤ ¦b - a¦ / 2 ^ k"
using n by (simp add: divide_left_mono)
also note k
finally show "¦(b - a) / 2 ^ n¦ < r" .
qed
then show "∃k. ∀n≥k. ¦(b - a) / 2 ^ n¦ < r" ..
qed
then have "Real B = Real A"
by (simp add: eq_Real ‹cauchy A› ‹cauchy B› width)
ultimately show "∃y. (∀x∈S. x ≤ y) ∧ (∀z. (∀x∈S. x ≤ z) ⟶ y ≤ z)"
by force
qed

instantiation real :: linear_continuum
begin

subsection ‹Supremum of a set of reals›

definition "Sup X = (LEAST z::real. ∀x∈X. x ≤ z)"
definition "Inf X = - Sup (uminus ` X)" for X :: "real set"

instance
proof
show Sup_upper: "x ≤ Sup X"
if "x ∈ X" "bdd_above X"
for x :: real and X :: "real set"
proof -
from that obtain s where s: "∀y∈X. y ≤ s" "⋀z. ∀y∈X. y ≤ z ⟹ s ≤ z"
using complete_real[of X] unfolding bdd_above_def by blast
then show ?thesis
unfolding Sup_real_def by (rule LeastI2_order) (auto simp: that)
qed
show Sup_least: "Sup X ≤ z"
if "X ≠ {}" and z: "⋀x. x ∈ X ⟹ x ≤ z"
for z :: real and X :: "real set"
proof -
from that obtain s where s: "∀y∈X. y ≤ s" "⋀z. ∀y∈X. y ≤ z ⟹ s ≤ z"
using complete_real [of X] by blast
then have "Sup X = s"
unfolding Sup_real_def by (best intro: Least_equality)
also from s z have "… ≤ z"
by blast
finally show ?thesis .
qed
show "Inf X ≤ x" if "x ∈ X" "bdd_below X"
for x :: real and X :: "real set"
using Sup_upper [of "-x" "uminus ` X"] by (auto simp: Inf_real_def that)
show "z ≤ Inf X" if "X ≠ {}" "⋀x. x ∈ X ⟹ z ≤ x"
for z :: real and X :: "real set"
using Sup_least [of "uminus ` X" "- z"] by (force simp: Inf_real_def that)
show "∃a b::real. a ≠ b"
using zero_neq_one by blast
qed

end

subsection ‹Hiding implementation details›

hide_const (open) vanishes cauchy positive Real

declare Real_induct [induct del]
declare Abs_real_induct [induct del]
declare Abs_real_cases [cases del]

lifting_update real.lifting
lifting_forget real.lifting

subsection ‹More Lemmas›

text ‹BH: These lemmas should not be necessary; they should be
covered by existing simp rules and simplification procedures.›

lemma real_mult_less_iff1 [simp]: "0 < z ⟹ x * z < y * z ⟷ x < y"
for x y z :: real
by simp (* solved by linordered_ring_less_cancel_factor simproc *)

lemma real_mult_le_cancel_iff1 [simp]: "0 < z ⟹ x * z ≤ y * z ⟷ x ≤ y"
for x y z :: real
by simp (* solved by linordered_ring_le_cancel_factor simproc *)

lemma real_mult_le_cancel_iff2 [simp]: "0 < z ⟹ z * x ≤ z * y ⟷ x ≤ y"
for x y z :: real
by simp (* solved by linordered_ring_le_cancel_factor simproc *)

subsection ‹Embedding numbers into the Reals›

abbreviation real_of_nat :: "nat ⇒ real"
where "real_of_nat ≡ of_nat"

abbreviation real :: "nat ⇒ real"
where "real ≡ of_nat"

abbreviation real_of_int :: "int ⇒ real"
where "real_of_int ≡ of_int"

abbreviation real_of_rat :: "rat ⇒ real"
where "real_of_rat ≡ of_rat"

declare [[coercion_enabled]]

declare [[coercion "of_nat :: nat ⇒ int"]]
declare [[coercion "of_nat :: nat ⇒ real"]]
declare [[coercion "of_int :: int ⇒ real"]]

(* We do not add rat to the coerced types, this has often unpleasant side effects when writing
inverse (Suc n) which sometimes gets two coercions: of_rat (inverse (of_nat (Suc n))) *)

declare [[coercion_map map]]
declare [[coercion_map "λf g h x. g (h (f x))"]]
declare [[coercion_map "λf g (x,y). (f x, g y)"]]

declare of_int_eq_0_iff [algebra, presburger]
declare of_int_eq_1_iff [algebra, presburger]
declare of_int_eq_iff [algebra, presburger]
declare of_int_less_0_iff [algebra, presburger]
declare of_int_less_1_iff [algebra, presburger]
declare of_int_less_iff [algebra, presburger]
declare of_int_le_0_iff [algebra, presburger]
declare of_int_le_1_iff [algebra, presburger]
declare of_int_le_iff [algebra, presburger]
declare of_int_0_less_iff [algebra, presburger]
declare of_int_0_le_iff [algebra, presburger]
declare of_int_1_less_iff [algebra, presburger]
declare of_int_1_le_iff [algebra, presburger]

lemma int_less_real_le: "n < m ⟷ real_of_int n + 1 ≤ real_of_int m"
proof -
have "(0::real) ≤ 1"
by (metis less_eq_real_def zero_less_one)
then show ?thesis
by (metis floor_of_int less_floor_iff)
qed

lemma int_le_real_less: "n ≤ m ⟷ real_of_int n < real_of_int m + 1"
by (meson int_less_real_le not_le)

lemma real_of_int_div_aux:
"(real_of_int x) / (real_of_int d) =
real_of_int (x div d) + (real_of_int (x mod d)) / (real_of_int d)"
proof -
have "x = (x div d) * d + x mod d"
by auto
then have "real_of_int x = real_of_int (x div d) * real_of_int d + real_of_int(x mod d)"
then have "real_of_int x / real_of_int d = … / real_of_int d"
by simp
then show ?thesis
qed

lemma real_of_int_div:
"d dvd n ⟹ real_of_int (n div d) = real_of_int n / real_of_int d" for d n :: int

lemma real_of_int_div2: "0 ≤ real_of_int n / real_of_int x - real_of_int (n div x)"
proof (cases "x = 0")
case False
then show ?thesis
by (metis diff_ge_0_iff_ge floor_divide_of_int_eq of_int_floor_le)
qed simp

lemma real_of_int_div3: "real_of_int n / real_of_int x - real_of_int (n div x) ≤ 1"

lemma real_of_int_div4: "real_of_int (n div x) ≤ real_of_int n / real_of_int x"
using real_of_int_div2 [of n x] by simp

subsection ‹Embedding the Naturals into the Reals›

lemma real_of_card: "real (card A) = sum (λx. 1) A"
by simp

lemma nat_less_real_le: "n < m ⟷ real n + 1 ≤ real m"
by (metis discrete of_nat_1 of_nat_add of_nat_le_iff)

lemma nat_le_real_less: "n ≤ m ⟷ real n < real m + 1"
for m n :: nat
by (meson nat_less_real_le not_le)

lemma real_of_nat_div_aux: "real x / real d = real (x div d) + real (x mod d) / real d"
proof -
have "x = (x div d) * d + x mod d"
by auto
then have "real x = real (x div d) * real d + real(x mod d)"
then have "real x / real d = … / real d"
by simp
then show ?thesis
qed

lemma real_of_nat_div: "d dvd n ⟹ real(n div d) = real n / real d"
by (subst real_of_nat_div_aux) (auto simp add: dvd_eq_mod_eq_0 [symmetric])

lemma real_of_nat_div2: "0 ≤ real n / real x - real (n div x)" for n x :: nat
by (metis floor_divide_of_nat_eq of_int_floor_le of_int_of_nat_eq)

lemma real_of_nat_div3: "real n / real x - real (n div x) ≤ 1" for n x :: nat
proof (cases "x = 0")
case False
then show ?thesis
by (metis of_int_of_nat_eq real_of_int_div3 zdiv_int)
qed auto

lemma real_of_nat_div4: "real (n div x) ≤ real n / real x" for n x :: nat
using real_of_nat_div2 [of n x] by simp

subsection ‹The Archimedean Property of the Reals›

lemma real_arch_inverse: "0 < e ⟷ (∃n::nat. n ≠ 0 ∧ 0 < inverse (real n) ∧ inverse (real n) < e)"
using reals_Archimedean[of e] less_trans[of 0 "1 / real n" e for n::nat]
by (auto simp add: field_simps cong: conj_cong simp del: of_nat_Suc)

lemma reals_Archimedean3: "0 < x ⟹ ∀y. ∃n. y < real n * x"
by (auto intro: ex_less_of_nat_mult)

lemma real_archimedian_rdiv_eq_0:
assumes x0: "x ≥ 0"
and c: "c ≥ 0"
and xc: "⋀m::nat. m > 0 ⟹ real m * x ≤ c"
shows "x = 0"
by (metis reals_Archimedean3 dual_order.order_iff_strict le0 le_less_trans not_le x0 xc)

subsection ‹Rationals›

lemma Rats_abs_iff[simp]:
"¦(x::real)¦ ∈ ℚ ⟷ x ∈ ℚ"

lemma Rats_eq_int_div_int: "ℚ = {real_of_int i / real_of_int j | i j. j ≠ 0}"  (is "_ = ?S")
proof
show "ℚ ⊆ ?S"
proof
fix x :: real
assume "x ∈ ℚ"
then obtain r where "x = of_rat r"
unfolding Rats_def ..
have "of_rat r ∈ ?S"
by (cases r) (auto simp add: of_rat_rat)
then show "x ∈ ?S"
using ‹x = of_rat r› by simp
qed
next
show "?S ⊆ ℚ"
proof (auto simp: Rats_def)
fix i j :: int
assume "j ≠ 0"
then have "real_of_int i / real_of_int j = of_rat (Fract i j)"
then show "real_of_int i / real_of_int j ∈ range of_rat"
by blast
qed
qed

lemma Rats_eq_int_div_nat: "ℚ = { real_of_int i / real n | i n. n ≠ 0}"
proof (auto simp: Rats_eq_int_div_int)
fix i j :: int
assume "j ≠ 0"
show "∃(i'::int) (n::nat). real_of_int i / real_of_int j = real_of_int i' / real n ∧ 0 < n"
proof (cases "j > 0")
case True
then have "real_of_int i / real_of_int j = real_of_int i / real (nat j) ∧ 0 < nat j"
by simp
then show ?thesis by blast
next
case False
with ‹j ≠ 0›
have "real_of_int i / real_of_int j = real_of_int (- i) / real (nat (- j)) ∧ 0 < nat (- j)"
by simp
then show ?thesis by blast
qed
next
fix i :: int and n :: nat
assume "0 < n"
then have "real_of_int i / real n = real_of_int i / real_of_int(int n) ∧ int n ≠ 0"
by simp
then show "∃i' j. real_of_int i / real n = real_of_int i' / real_of_int j ∧ j ≠ 0"
by blast
qed

lemma Rats_abs_nat_div_natE:
assumes "x ∈ ℚ"
obtains m n :: nat where "n ≠ 0" and "¦x¦ = real m / real n" and "coprime m n"
proof -
from ‹x ∈ ℚ› obtain i :: int and n :: nat where "n ≠ 0" and "x = real_of_int i / real n"
then have "¦x¦ = real (nat ¦i¦) / real n" by simp
then obtain m :: nat where x_rat: "¦x¦ = real m / real n" by blast
let ?gcd = "gcd m n"
from ‹n ≠ 0› have gcd: "?gcd ≠ 0" by simp
let ?k = "m div ?gcd"
let ?l = "n div ?gcd"
let ?gcd' = "gcd ?k ?l"
have "?gcd dvd m" ..
then have gcd_k: "?gcd * ?k = m"
by (rule dvd_mult_div_cancel)
have "?gcd dvd n" ..
then have gcd_l: "?gcd * ?l = n"
by (rule dvd_mult_div_cancel)
from ‹n ≠ 0› and gcd_l have "?gcd * ?l ≠ 0" by simp
then have "?l ≠ 0" by (blast dest!: mult_not_zero)
moreover
have "¦x¦ = real ?k / real ?l"
proof -
from gcd have "real ?k / real ?l = real (?gcd * ?k) / real (?gcd * ?l)"
also from gcd_k and gcd_l have "… = real m / real n" by simp
also from x_rat have "… = ¦x¦" ..
finally show ?thesis ..
qed
moreover
have "?gcd' = 1"
proof -
have "?gcd * ?gcd' = gcd (?gcd * ?k) (?gcd * ?l)"
by (rule gcd_mult_distrib_nat)
with gcd_k gcd_l have "?gcd * ?gcd' = ?gcd" by simp
with gcd show ?thesis by auto
qed
then have "coprime ?k ?l"
by (simp only: coprime_iff_gcd_eq_1)
ultimately show ?thesis ..
qed

subsection ‹Density of the Rational Reals in the Reals›

text ‹
This density proof is due to Stefan Richter and was ported by TN.  The
original source is ∗‹Real Analysis› by H.L. Royden.
It employs the Archimedean property of the reals.›

lemma Rats_dense_in_real:
fixes x :: real
assumes "x < y"
shows "∃r∈ℚ. x < r ∧ r < y"
proof -
from ‹x < y› have "0 < y - x" by simp
with reals_Archimedean obtain q :: nat where q: "inverse (real q) < y - x" and "0 < q"
by blast
define p where "p = ⌈y * real q⌉ - 1"
define r where "r = of_int p / real q"
from q have "x < y - inverse (real q)"
by simp
also from ‹0 < q› have "y - inverse (real q) ≤ r"
by (simp add: r_def p_def le_divide_eq left_diff_distrib)
finally have "x < r" .
moreover from ‹0 < q› have "r < y"
by (simp add: r_def p_def divide_less_eq diff_less_eq less_ceiling_iff [symmetric])
moreover have "r ∈ ℚ"
ultimately show ?thesis by blast
qed

lemma of_rat_dense:
fixes x y :: real
assumes "x < y"
shows "∃q :: rat. x < of_rat q ∧ of_rat q < y"
using Rats_dense_in_real [OF ‹x < y›]
by (auto elim: Rats_cases)

subsection ‹Numerals and Arithmetic›

declaration ‹
K (Lin_Arith.add_inj_thms [@{thm of_nat_le_iff} RS iffD2, @{thm of_nat_eq_iff} RS iffD2]
(* not needed because x < (y::nat) can be rewritten as Suc x <= y: of_nat_less_iff RS iffD2 *)
#> Lin_Arith.add_inj_thms [@{thm of_int_le_iff} RS iffD2, @{thm of_nat_eq_iff} RS iffD2]
(* not needed because x < (y::int) can be rewritten as x + 1 <= y: of_int_less_iff RS iffD2 *)
@{thm of_nat_mult}, @{thm of_int_0}, @{thm of_int_1},
@{thm of_int_add}, @{thm of_int_minus}, @{thm of_int_diff},
@{thm of_int_mult}, @{thm of_int_of_nat_eq},
@{thm of_nat_numeral}, @{thm of_nat_numeral}, @{thm of_int_neg_numeral}]
#> Lin_Arith.add_inj_const (@{const_name of_nat}, @{typ "nat ⇒ real"})
#> Lin_Arith.add_inj_const (@{const_name of_int}, @{typ "int ⇒ real"}))
›

subsection ‹Simprules combining ‹x + y› and ‹0›› (* FIXME ARE THEY NEEDED? *)

lemma real_add_minus_iff [simp]: "x + - a = 0 ⟷ x = a"
for x a :: real
by arith

lemma real_add_less_0_iff: "x + y < 0 ⟷ y < - x"
for x y :: real
by auto

lemma real_0_less_add_iff: "0 < x + y ⟷ - x < y"
for x y :: real
by auto

lemma real_add_le_0_iff: "x + y ≤ 0 ⟷ y ≤ - x"
for x y :: real
by auto

lemma real_0_le_add_iff: "0 ≤ x + y ⟷ - x ≤ y"
for x y :: real
by auto

lemma two_realpow_ge_one: "(1::real) ≤ 2 ^ n"
by simp

(* FIXME: declare this [simp] for all types, or not at all *)
declare sum_squares_eq_zero_iff [simp] sum_power2_eq_zero_iff [simp]

lemma real_minus_mult_self_le [simp]: "- (u * u) ≤ x * x"
for u x :: real
by (rule order_trans [where y = 0]) auto

lemma realpow_square_minus_le [simp]: "- u⇧2 ≤ x⇧2"
for u x :: real

subsection ‹Density of the Reals›

lemma field_lbound_gt_zero: "0 < d1 ⟹ 0 < d2 ⟹ ∃e. 0 < e ∧ e < d1 ∧ e < d2"
for d1 d2 :: "'a::linordered_field"
by (rule exI [where x = "min d1 d2 / 2"]) (simp add: min_def)

lemma field_less_half_sum: "x < y ⟹ x < (x + y) / 2"
for x y :: "'a::linordered_field"
by auto

lemma field_sum_of_halves: "x / 2 + x / 2 = x"
for x :: "'a::linordered_field"
by simp

subsection ‹Floor and Ceiling Functions from the Reals to the Integers›

(* FIXME: theorems for negative numerals. Many duplicates, e.g. from Archimedean_Field.thy. *)

lemma real_of_nat_less_numeral_iff [simp]: "real n < numeral w ⟷ n < numeral w"
for n :: nat
by (metis of_nat_less_iff of_nat_numeral)

lemma numeral_less_real_of_nat_iff [simp]: "numeral w < real n ⟷ numeral w < n"
for n :: nat
by (metis of_nat_less_iff of_nat_numeral)

lemma numeral_le_real_of_nat_iff [simp]: "numeral n ≤ real m ⟷ numeral n ≤ m"
for m :: nat
by (metis not_le real_of_nat_less_numeral_iff)

lemma of_int_floor_cancel [simp]: "of_int ⌊x⌋ = x ⟷ (∃n::int. x = of_int n)"
by (metis floor_of_int)

lemma floor_eq: "real_of_int n < x ⟹ x < real_of_int n + 1 ⟹ ⌊x⌋ = n"
by linarith

lemma floor_eq2: "real_of_int n ≤ x ⟹ x < real_of_int n + 1 ⟹ ⌊x⌋ = n"
by (fact floor_unique)

lemma floor_eq3: "real n < x ⟹ x < real (Suc n) ⟹ nat ⌊x⌋ = n"
by linarith

lemma floor_eq4: "real n ≤ x ⟹ x < real (Suc n) ⟹ nat ⌊x⌋ = n"
by linarith

lemma real_of_int_floor_ge_diff_one [simp]: "r - 1 ≤ real_of_int ⌊r⌋"
by linarith

lemma real_of_int_floor_gt_diff_one [simp]: "r - 1 < real_of_int ⌊r⌋"
by linarith

lemma real_of_int_floor_add_one_ge [simp]: "r ≤ real_of_int ⌊r⌋ + 1"
by linarith

lemma real_of_int_floor_add_one_gt [simp]: "r < real_of_int ⌊r⌋ + 1"
by linarith

lemma floor_divide_real_eq_div:
assumes "0 ≤ b"
shows "⌊a / real_of_int b⌋ = ⌊a⌋ div b"
proof (cases "b = 0")
case True
then show ?thesis by simp
next
case False
with assms have b: "b > 0" by simp
have "j = i div b"
if "real_of_int i ≤ a" "a < 1 + real_of_int i"
"real_of_int j * real_of_int b ≤ a" "a < real_of_int b + real_of_int j * real_of_int b"
for i j :: int
proof -
from that have "i < b + j * b"
by (metis le_less_trans of_int_add of_int_less_iff of_int_mult)
moreover have "j * b < 1 + i"
proof -
have "real_of_int (j * b) < real_of_int i + 1"
using ‹a < 1 + real_of_int i› ‹real_of_int j * real_of_int b ≤ a› by force
then show "j * b < 1 + i" by linarith
qed
ultimately have "(j - i div b) * b ≤ i mod b" "i mod b < ((j - i div b) + 1) * b"
by (auto simp: field_simps)
then have "(j - i div b) * b < 1 * b" "0 * b < ((j - i div b) + 1) * b"
using pos_mod_bound [OF b, of i] pos_mod_sign [OF b, of i]
by linarith+
then show ?thesis using b unfolding mult_less_cancel_right by auto
qed
with b show ?thesis by (auto split: floor_split simp: field_simps)
qed

lemma floor_one_divide_eq_div_numeral [simp]:
"⌊1 / numeral b::real⌋ = 1 div numeral b"
by (metis floor_divide_of_int_eq of_int_1 of_int_numeral)

lemma floor_minus_one_divide_eq_div_numeral [simp]:
"⌊- (1 / numeral b)::real⌋ = - 1 div numeral b"
by (metis (mono_tags, hide_lams) div_minus_right minus_divide_right
floor_divide_of_int_eq of_int_neg_numeral of_int_1)

lemma floor_divide_eq_div_numeral [simp]:
"⌊numeral a / numeral b::real⌋ = numeral a div numeral b"
by (metis floor_divide_of_int_eq of_int_numeral)

lemma floor_minus_divide_eq_div_numeral [simp]:
"⌊- (numeral a / numeral b)::real⌋ = - numeral a div numeral b"
by (metis divide_minus_left floor_divide_of_int_eq of_int_neg_numeral of_int_numeral)

lemma of_int_ceiling_cancel [simp]: "of_int ⌈x⌉ = x ⟷ (∃n::int. x = of_int n)"
using ceiling_of_int by metis

lemma ceiling_eq: "of_int n < x ⟹ x ≤ of_int n + 1 ⟹ ⌈x⌉ = n + 1"

lemma of_int_ceiling_diff_one_le [simp]: "of_int ⌈r⌉ - 1 ≤ r"
by linarith

lemma of_int_ceiling_le_add_one [simp]: "of_int ⌈r⌉ ≤ r + 1"
by linarith

lemma ceiling_le: "x ≤ of_int a ⟹ ⌈x⌉ ≤ a"

lemma ceiling_divide_eq_div: "⌈of_int a / of_int b⌉ = - (- a div b)"
by (metis ceiling_def floor_divide_of_int_eq minus_divide_left of_int_minus)

lemma ceiling_divide_eq_div_numeral [simp]:
"⌈numeral a / numeral b :: real⌉ = - (- numeral a div numeral b)"
using ceiling_divide_eq_div[of "numeral a" "numeral b"] by simp

lemma ceiling_minus_divide_eq_div_numeral [simp]:
"⌈- (numeral a / numeral b :: real)⌉ = - (numeral a div numeral b)"
using ceiling_divide_eq_div[of "- numeral a" "numeral b"] by simp

text ‹
The following lemmas are remnants of the erstwhile functions natfloor
and natceiling.
›

lemma nat_floor_neg: "x ≤ 0 ⟹ nat ⌊x⌋ = 0"
for x :: real
by linarith

lemma le_nat_floor: "real x ≤ a ⟹ x ≤ nat ⌊a⌋"
by linarith

lemma le_mult_nat_floor: "nat ⌊a⌋ * nat ⌊b⌋ ≤ nat ⌊a * b⌋"
by (cases "0 ≤ a ∧ 0 ≤ b")
(auto simp add: nat_mult_distrib[symmetric] nat_mono le_mult_floor)

lemma nat_ceiling_le_eq [simp]: "nat ⌈x⌉ ≤ a ⟷ x ≤ real a"
by linarith

lemma real_nat_ceiling_ge: "x ≤ real (nat ⌈x⌉)"
by linarith

lemma Rats_no_top_le: "∃q ∈ ℚ. x ≤ q"
for x :: real
by (auto intro!: bexI[of _ "of_nat (nat ⌈x⌉)"]) linarith

lemma Rats_no_bot_less: "∃q ∈ ℚ. q < x" for x :: real
by (auto intro!: bexI[of _ "of_int (⌊x⌋ - 1)"]) linarith

subsection ‹Exponentiation with floor›

lemma floor_power:
assumes "x = of_int ⌊x⌋"
shows "⌊x ^ n⌋ = ⌊x⌋ ^ n"
proof -
have "x ^ n = of_int (⌊x⌋ ^ n)"
using assms by (induct n arbitrary: x) simp_all
then show ?thesis by (metis floor_of_int)
qed

lemma floor_numeral_power [simp]: "⌊numeral x ^ n⌋ = numeral x ^ n"
by (metis floor_of_int of_int_numeral of_int_power)

lemma ceiling_numeral_power [simp]: "⌈numeral x ^ n⌉ = numeral x ^ n"
by (metis ceiling_of_int of_int_numeral of_int_power)

subsection ‹Implementation of rational real numbers›

text ‹Formal constructor›

definition Ratreal :: "rat ⇒ real"
where [code_abbrev, simp]: "Ratreal = real_of_rat"

code_datatype Ratreal

text ‹Quasi-Numerals›

lemma [code_abbrev]:
"real_of_rat (numeral k) = numeral k"
"real_of_rat (- numeral k) = - numeral k"
"real_of_rat (rat_of_int a) = real_of_int a"
by simp_all

lemma [code_post]:
"real_of_rat 0 = 0"
"real_of_rat 1 = 1"
"real_of_rat (- 1) = - 1"
"real_of_rat (1 / numeral k) = 1 / numeral k"
"real_of_rat (numeral k / numeral l) = numeral k / numeral l"
"real_of_rat (- (1 / numeral k)) = - (1 / numeral k)"
"real_of_rat (- (numeral k / numeral l)) = - (numeral k / numeral l)"

text ‹Operations›

lemma zero_real_code [code]: "0 = Ratreal 0"
by simp

lemma one_real_code [code]: "1 = Ratreal 1"
by simp

instantiation real :: equal
begin

definition "HOL.equal x y ⟷ x - y = 0" for x :: real

instance by standard (simp add: equal_real_def)

lemma real_equal_code [code]: "HOL.equal (Ratreal x) (Ratreal y) ⟷ HOL.equal x y"

lemma [code nbe]: "HOL.equal x x ⟷ True"
for x :: real
by (rule equal_refl)

end

lemma real_less_eq_code [code]: "Ratreal x ≤ Ratreal y ⟷ x ≤ y"

lemma real_less_code [code]: "Ratreal x < Ratreal y ⟷ x < y"

lemma real_plus_code [code]: "Ratreal x + Ratreal y = Ratreal (x + y)"

lemma real_times_code [code]: "Ratreal x * Ratreal y = Ratreal (x * y)"

lemma real_uminus_code [code]: "- Ratreal x = Ratreal (- x)"

lemma real_minus_code [code]: "Ratreal x - Ratreal y = Ratreal (x - y)"

lemma real_inverse_code [code]: "inverse (Ratreal x) = Ratreal (inverse x)"

lemma real_divide_code [code]: "Ratreal x / Ratreal y = Ratreal (x / y)"

lemma real_floor_code [code]: "⌊Ratreal x⌋ = ⌊x⌋"
by (metis Ratreal_def floor_le_iff floor_unique le_floor_iff
of_int_floor_le of_rat_of_int_eq real_less_eq_code)

text ‹Quickcheck›

definition (in term_syntax)
valterm_ratreal :: "rat × (unit ⇒ Code_Evaluation.term) ⇒ real × (unit ⇒ Code_Evaluation.term)"
where [code_unfold]: "valterm_ratreal k = Code_Evaluation.valtermify Ratreal {⋅} k"

notation fcomp (infixl "∘>" 60)
notation scomp (infixl "∘→" 60)

instantiation real :: random
begin

definition
"Quickcheck_Random.random i = Quickcheck_Random.random i ∘→ (λr. Pair (valterm_ratreal r))"

instance ..

end

no_notation fcomp (infixl "∘>" 60)
no_notation scomp (infixl "∘→" 60)

instantiation real :: exhaustive
begin

definition
"exhaustive_real f d = Quickcheck_Exhaustive.exhaustive (λr. f (Ratreal r)) d"

instance ..

end

instantiation real :: full_exhaustive
begin

definition
"full_exhaustive_real f d = Quickcheck_Exhaustive.full_exhaustive (λr. f (valterm_ratreal r)) d"

instance ..

end

instantiation real :: narrowing
begin

definition
"narrowing_real = Quickcheck_Narrowing.apply (Quickcheck_Narrowing.cons Ratreal) narrowing"

instance ..

end

subsection ‹Setup for Nitpick›

declaration ‹
Nitpick_HOL.register_frac_type @{type_name real}
[(@{const_name zero_real_inst.zero_real}, @{const_name Nitpick.zero_frac}),
(@{const_name one_real_inst.one_real}, @{const_name Nitpick.one_frac}),
(@{const_name plus_real_inst.plus_real}, @{const_name Nitpick.plus_frac}),
(@{const_name times_real_inst.times_real}, @{const_name Nitpick.times_frac}),
(@{const_name uminus_real_inst.uminus_real}, @{const_name Nitpick.uminus_frac}),
(@{const_name inverse_real_inst.inverse_real}, @{const_name Nitpick.inverse_frac}),
(@{const_name ord_real_inst.less_real}, @{const_name Nitpick.less_frac}),
(@{const_name ord_real_inst.less_eq_real}, @{const_name Nitpick.less_eq_frac})]
›

lemmas [nitpick_unfold] = inverse_real_inst.inverse_real one_real_inst.one_real
ord_real_inst.less_real ord_real_inst.less_eq_real plus_real_inst.plus_real
times_real_inst.times_real uminus_real_inst.uminus_real
zero_real_inst.zero_real

subsection ‹Setup for SMT›

ML_file "Tools/SMT/smt_real.ML"
ML_file "Tools/SMT/z3_real.ML"

lemma [z3_rule]:
"0 + x = x"
"x + 0 = x"
"0 * x = 0"
"1 * x = x"
"-x = -1 * x"
"x + y = y + x"
for x y :: real
by auto

subsection ‹Setup for Argo›

ML_file "Tools/Argo/argo_real.ML"

end
```