src/HOL/Rat.thy

tuned proofs -- clarified flow of facts wrt. calculation;

(*  Title:  HOL/Rat.thy
    Author: Markus Wenzel, TU Muenchen
*)

header {* Rational numbers *}

theory Rat
imports GCD Archimedean_Field
begin

subsection {* Rational numbers as quotient *}

subsubsection {* Construction of the type of rational numbers *}

definition
  ratrel :: "(int \<times> int) \<Rightarrow> (int \<times> int) \<Rightarrow> bool" where
  "ratrel = (\<lambda>x y. snd x \<noteq> 0 \<and> snd y \<noteq> 0 \<and> fst x * snd y = fst y * snd x)"

lemma ratrel_iff [simp]:
  "ratrel x y \<longleftrightarrow> snd x \<noteq> 0 \<and> snd y \<noteq> 0 \<and> fst x * snd y = fst y * snd x"
  by (simp add: ratrel_def)

lemma exists_ratrel_refl: "\<exists>x. ratrel x x"
  by (auto intro!: one_neq_zero)

lemma symp_ratrel: "symp ratrel"
  by (simp add: ratrel_def symp_def)

lemma transp_ratrel: "transp ratrel"
proof (rule transpI, unfold split_paired_all)
  fix a b a' b' a'' b'' :: int
  assume A: "ratrel (a, b) (a', b')"
  assume B: "ratrel (a', b') (a'', b'')"
  have "b' * (a * b'') = b'' * (a * b')" by simp
  also from A have "a * b' = a' * b" by auto
  also have "b'' * (a' * b) = b * (a' * b'')" by simp
  also from B have "a' * b'' = a'' * b'" by auto
  also have "b * (a'' * b') = b' * (a'' * b)" by simp
  finally have "b' * (a * b'') = b' * (a'' * b)" .
  moreover from B have "b' \<noteq> 0" by auto
  ultimately have "a * b'' = a'' * b" by simp
  with A B show "ratrel (a, b) (a'', b'')" by auto
qed

lemma part_equivp_ratrel: "part_equivp ratrel"
  by (rule part_equivpI [OF exists_ratrel_refl symp_ratrel transp_ratrel])

quotient_type rat = "int \<times> int" / partial: "ratrel"
  morphisms Rep_Rat Abs_Rat
  by (rule part_equivp_ratrel)

lemma Domainp_cr_rat [transfer_domain_rule]: "Domainp pcr_rat = (\<lambda>x. snd x \<noteq> 0)"
by (simp add: rat.domain_eq)

subsubsection {* Representation and basic operations *}

lift_definition Fract :: "int \<Rightarrow> int \<Rightarrow> rat"
  is "\<lambda>a b. if b = 0 then (0, 1) else (a, b)"
  by simp

lemma eq_rat:
  shows "\<And>a b c d. b \<noteq> 0 \<Longrightarrow> d \<noteq> 0 \<Longrightarrow> Fract a b = Fract c d \<longleftrightarrow> a * d = c * b"
  and "\<And>a. Fract a 0 = Fract 0 1"
  and "\<And>a c. Fract 0 a = Fract 0 c"
  by (transfer, simp)+

lemma Rat_cases [case_names Fract, cases type: rat]:
  assumes "\<And>a b. q = Fract a b \<Longrightarrow> b > 0 \<Longrightarrow> coprime a b \<Longrightarrow> C"
  shows C
proof -
  obtain a b :: int where "q = Fract a b" and "b \<noteq> 0"
    by transfer simp
  let ?a = "a div gcd a b"
  let ?b = "b div gcd a b"
  from `b \<noteq> 0` have "?b * gcd a b = b"
    by (simp add: dvd_div_mult_self)
  with `b \<noteq> 0` have "?b \<noteq> 0" by auto
  from `q = Fract a b` `b \<noteq> 0` `?b \<noteq> 0` have q: "q = Fract ?a ?b"
    by (simp add: eq_rat dvd_div_mult mult_commute [of a])
  from `b \<noteq> 0` have coprime: "coprime ?a ?b"
    by (auto intro: div_gcd_coprime_int)
  show C proof (cases "b > 0")
    case True
    note assms
    moreover note q
    moreover from True have "?b > 0" by (simp add: nonneg1_imp_zdiv_pos_iff)
    moreover note coprime
    ultimately show C .
  next
    case False
    note assms
    moreover have "q = Fract (- ?a) (- ?b)" unfolding q by transfer simp
    moreover from False `b \<noteq> 0` have "- ?b > 0" by (simp add: pos_imp_zdiv_neg_iff)
    moreover from coprime have "coprime (- ?a) (- ?b)" by simp
    ultimately show C .
  qed
qed

lemma Rat_induct [case_names Fract, induct type: rat]:
  assumes "\<And>a b. b > 0 \<Longrightarrow> coprime a b \<Longrightarrow> P (Fract a b)"
  shows "P q"
  using assms by (cases q) simp

instantiation rat :: field_inverse_zero
begin

lift_definition zero_rat :: "rat" is "(0, 1)"
  by simp

lift_definition one_rat :: "rat" is "(1, 1)"
  by simp

lemma Zero_rat_def: "0 = Fract 0 1"
  by transfer simp

lemma One_rat_def: "1 = Fract 1 1"
  by transfer simp

lift_definition plus_rat :: "rat \<Rightarrow> rat \<Rightarrow> rat"
  is "\<lambda>x y. (fst x * snd y + fst y * snd x, snd x * snd y)"
  by (clarsimp, simp add: distrib_right, simp add: mult_ac)

lemma add_rat [simp]:
  assumes "b \<noteq> 0" and "d \<noteq> 0"
  shows "Fract a b + Fract c d = Fract (a * d + c * b) (b * d)"
  using assms by transfer simp

lift_definition uminus_rat :: "rat \<Rightarrow> rat" is "\<lambda>x. (- fst x, snd x)"
  by simp

lemma minus_rat [simp]: "- Fract a b = Fract (- a) b"
  by transfer simp

lemma minus_rat_cancel [simp]: "Fract (- a) (- b) = Fract a b"
  by (cases "b = 0") (simp_all add: eq_rat)

definition
  diff_rat_def: "q - r = q + - (r::rat)"

lemma diff_rat [simp]:
  assumes "b \<noteq> 0" and "d \<noteq> 0"
  shows "Fract a b - Fract c d = Fract (a * d - c * b) (b * d)"
  using assms by (simp add: diff_rat_def)

lift_definition times_rat :: "rat \<Rightarrow> rat \<Rightarrow> rat"
  is "\<lambda>x y. (fst x * fst y, snd x * snd y)"
  by (simp add: mult_ac)

lemma mult_rat [simp]: "Fract a b * Fract c d = Fract (a * c) (b * d)"
  by transfer simp

lemma mult_rat_cancel:
  assumes "c \<noteq> 0"
  shows "Fract (c * a) (c * b) = Fract a b"
  using assms by transfer simp

lift_definition inverse_rat :: "rat \<Rightarrow> rat"
  is "\<lambda>x. if fst x = 0 then (0, 1) else (snd x, fst x)"
  by (auto simp add: mult_commute)

lemma inverse_rat [simp]: "inverse (Fract a b) = Fract b a"
  by transfer simp

definition
  divide_rat_def: "q / r = q * inverse (r::rat)"

lemma divide_rat [simp]: "Fract a b / Fract c d = Fract (a * d) (b * c)"
  by (simp add: divide_rat_def)

instance proof
  fix q r s :: rat
  show "(q * r) * s = q * (r * s)"
    by transfer simp
  show "q * r = r * q"
    by transfer simp
  show "1 * q = q"
    by transfer simp
  show "(q + r) + s = q + (r + s)"
    by transfer (simp add: algebra_simps)
  show "q + r = r + q"
    by transfer simp
  show "0 + q = q"
    by transfer simp
  show "- q + q = 0"
    by transfer simp
  show "q - r = q + - r"
    by (fact diff_rat_def)
  show "(q + r) * s = q * s + r * s"
    by transfer (simp add: algebra_simps)
  show "(0::rat) \<noteq> 1"
    by transfer simp
  { assume "q \<noteq> 0" thus "inverse q * q = 1"
    by transfer simp }
  show "q / r = q * inverse r"
    by (fact divide_rat_def)
  show "inverse 0 = (0::rat)"
    by transfer simp
qed

end

lemma of_nat_rat: "of_nat k = Fract (of_nat k) 1"
  by (induct k) (simp_all add: Zero_rat_def One_rat_def)

lemma of_int_rat: "of_int k = Fract k 1"
  by (cases k rule: int_diff_cases) (simp add: of_nat_rat)

lemma Fract_of_nat_eq: "Fract (of_nat k) 1 = of_nat k"
  by (rule of_nat_rat [symmetric])

lemma Fract_of_int_eq: "Fract k 1 = of_int k"
  by (rule of_int_rat [symmetric])

lemma rat_number_collapse:
  "Fract 0 k = 0"
  "Fract 1 1 = 1"
  "Fract (numeral w) 1 = numeral w"
  "Fract (neg_numeral w) 1 = neg_numeral w"
  "Fract k 0 = 0"
  using Fract_of_int_eq [of "numeral w"]
  using Fract_of_int_eq [of "neg_numeral w"]
  by (simp_all add: Zero_rat_def One_rat_def eq_rat)

lemma rat_number_expand:
  "0 = Fract 0 1"
  "1 = Fract 1 1"
  "numeral k = Fract (numeral k) 1"
  "neg_numeral k = Fract (neg_numeral k) 1"
  by (simp_all add: rat_number_collapse)

lemma Rat_cases_nonzero [case_names Fract 0]:
  assumes Fract: "\<And>a b. q = Fract a b \<Longrightarrow> b > 0 \<Longrightarrow> a \<noteq> 0 \<Longrightarrow> coprime a b \<Longrightarrow> C"
  assumes 0: "q = 0 \<Longrightarrow> C"
  shows C
proof (cases "q = 0")
  case True then show C using 0 by auto
next
  case False
  then obtain a b where "q = Fract a b" and "b > 0" and "coprime a b" by (cases q) auto
  with False have "0 \<noteq> Fract a b" by simp
  with `b > 0` have "a \<noteq> 0" by (simp add: Zero_rat_def eq_rat)
  with Fract `q = Fract a b` `b > 0` `coprime a b` show C by blast
qed

subsubsection {* Function @{text normalize} *}

lemma Fract_coprime: "Fract (a div gcd a b) (b div gcd a b) = Fract a b"
proof (cases "b = 0")
  case True then show ?thesis by (simp add: eq_rat)
next
  case False
  moreover have "b div gcd a b * gcd a b = b"
    by (rule dvd_div_mult_self) simp
  ultimately have "b div gcd a b \<noteq> 0" by auto
  with False show ?thesis by (simp add: eq_rat dvd_div_mult mult_commute [of a])
qed

definition normalize :: "int \<times> int \<Rightarrow> int \<times> int" where
  "normalize p = (if snd p > 0 then (let a = gcd (fst p) (snd p) in (fst p div a, snd p div a))
    else if snd p = 0 then (0, 1)
    else (let a = - gcd (fst p) (snd p) in (fst p div a, snd p div a)))"

lemma normalize_crossproduct:
  assumes "q \<noteq> 0" "s \<noteq> 0"
  assumes "normalize (p, q) = normalize (r, s)"
  shows "p * s = r * q"
proof -
  have aux: "p * gcd r s = sgn (q * s) * r * gcd p q \<Longrightarrow> q * gcd r s = sgn (q * s) * s * gcd p q \<Longrightarrow> p * s = q * r"
  proof -
    assume "p * gcd r s = sgn (q * s) * r * gcd p q" and "q * gcd r s = sgn (q * s) * s * gcd p q"
    then have "(p * gcd r s) * (sgn (q * s) * s * gcd p q) = (q * gcd r s) * (sgn (q * s) * r * gcd p q)" by simp
    with assms show "p * s = q * r" by (auto simp add: mult_ac sgn_times sgn_0_0)
  qed
  from assms show ?thesis
    by (auto simp add: normalize_def Let_def dvd_div_div_eq_mult mult_commute sgn_times split: if_splits intro: aux)
qed

lemma normalize_eq: "normalize (a, b) = (p, q) \<Longrightarrow> Fract p q = Fract a b"
  by (auto simp add: normalize_def Let_def Fract_coprime dvd_div_neg rat_number_collapse
    split:split_if_asm)

lemma normalize_denom_pos: "normalize r = (p, q) \<Longrightarrow> q > 0"
  by (auto simp add: normalize_def Let_def dvd_div_neg pos_imp_zdiv_neg_iff nonneg1_imp_zdiv_pos_iff
    split:split_if_asm)

lemma normalize_coprime: "normalize r = (p, q) \<Longrightarrow> coprime p q"
  by (auto simp add: normalize_def Let_def dvd_div_neg div_gcd_coprime_int
    split:split_if_asm)

lemma normalize_stable [simp]:
  "q > 0 \<Longrightarrow> coprime p q \<Longrightarrow> normalize (p, q) = (p, q)"
  by (simp add: normalize_def)

lemma normalize_denom_zero [simp]:
  "normalize (p, 0) = (0, 1)"
  by (simp add: normalize_def)

lemma normalize_negative [simp]:
  "q < 0 \<Longrightarrow> normalize (p, q) = normalize (- p, - q)"
  by (simp add: normalize_def Let_def dvd_div_neg dvd_neg_div)

text{*
  Decompose a fraction into normalized, i.e. coprime numerator and denominator:
*}

definition quotient_of :: "rat \<Rightarrow> int \<times> int" where
  "quotient_of x = (THE pair. x = Fract (fst pair) (snd pair) &
                   snd pair > 0 & coprime (fst pair) (snd pair))"

lemma quotient_of_unique:
  "\<exists>!p. r = Fract (fst p) (snd p) \<and> snd p > 0 \<and> coprime (fst p) (snd p)"
proof (cases r)
  case (Fract a b)
  then have "r = Fract (fst (a, b)) (snd (a, b)) \<and> snd (a, b) > 0 \<and> coprime (fst (a, b)) (snd (a, b))" by auto
  then show ?thesis proof (rule ex1I)
    fix p
    obtain c d :: int where p: "p = (c, d)" by (cases p)
    assume "r = Fract (fst p) (snd p) \<and> snd p > 0 \<and> coprime (fst p) (snd p)"
    with p have Fract': "r = Fract c d" "d > 0" "coprime c d" by simp_all
    have "c = a \<and> d = b"
    proof (cases "a = 0")
      case True with Fract Fract' show ?thesis by (simp add: eq_rat)
    next
      case False
      with Fract Fract' have *: "c * b = a * d" and "c \<noteq> 0" by (auto simp add: eq_rat)
      then have "c * b > 0 \<longleftrightarrow> a * d > 0" by auto
      with `b > 0` `d > 0` have "a > 0 \<longleftrightarrow> c > 0" by (simp add: zero_less_mult_iff)
      with `a \<noteq> 0` `c \<noteq> 0` have sgn: "sgn a = sgn c" by (auto simp add: not_less)
      from `coprime a b` `coprime c d` have "\<bar>a\<bar> * \<bar>d\<bar> = \<bar>c\<bar> * \<bar>b\<bar> \<longleftrightarrow> \<bar>a\<bar> = \<bar>c\<bar> \<and> \<bar>d\<bar> = \<bar>b\<bar>"
        by (simp add: coprime_crossproduct_int)
      with `b > 0` `d > 0` have "\<bar>a\<bar> * d = \<bar>c\<bar> * b \<longleftrightarrow> \<bar>a\<bar> = \<bar>c\<bar> \<and> d = b" by simp
      then have "a * sgn a * d = c * sgn c * b \<longleftrightarrow> a * sgn a = c * sgn c \<and> d = b" by (simp add: abs_sgn)
      with sgn * show ?thesis by (auto simp add: sgn_0_0)
    qed
    with p show "p = (a, b)" by simp
  qed
qed

lemma quotient_of_Fract [code]:
  "quotient_of (Fract a b) = normalize (a, b)"
proof -
  have "Fract a b = Fract (fst (normalize (a, b))) (snd (normalize (a, b)))" (is ?Fract)
    by (rule sym) (auto intro: normalize_eq)
  moreover have "0 < snd (normalize (a, b))" (is ?denom_pos)
    by (cases "normalize (a, b)") (rule normalize_denom_pos, simp)
  moreover have "coprime (fst (normalize (a, b))) (snd (normalize (a, b)))" (is ?coprime)
    by (rule normalize_coprime) simp
  ultimately have "?Fract \<and> ?denom_pos \<and> ?coprime" by blast
  with quotient_of_unique have
    "(THE p. Fract a b = Fract (fst p) (snd p) \<and> 0 < snd p \<and> coprime (fst p) (snd p)) = normalize (a, b)"
    by (rule the1_equality)
  then show ?thesis by (simp add: quotient_of_def)
qed

lemma quotient_of_number [simp]:
  "quotient_of 0 = (0, 1)"
  "quotient_of 1 = (1, 1)"
  "quotient_of (numeral k) = (numeral k, 1)"
  "quotient_of (neg_numeral k) = (neg_numeral k, 1)"
  by (simp_all add: rat_number_expand quotient_of_Fract)

lemma quotient_of_eq: "quotient_of (Fract a b) = (p, q) \<Longrightarrow> Fract p q = Fract a b"
  by (simp add: quotient_of_Fract normalize_eq)

lemma quotient_of_denom_pos: "quotient_of r = (p, q) \<Longrightarrow> q > 0"
  by (cases r) (simp add: quotient_of_Fract normalize_denom_pos)

lemma quotient_of_coprime: "quotient_of r = (p, q) \<Longrightarrow> coprime p q"
  by (cases r) (simp add: quotient_of_Fract normalize_coprime)

lemma quotient_of_inject:
  assumes "quotient_of a = quotient_of b"
  shows "a = b"
proof -
  obtain p q r s where a: "a = Fract p q"
    and b: "b = Fract r s"
    and "q > 0" and "s > 0" by (cases a, cases b)
  with assms show ?thesis by (simp add: eq_rat quotient_of_Fract normalize_crossproduct)
qed

lemma quotient_of_inject_eq:
  "quotient_of a = quotient_of b \<longleftrightarrow> a = b"
  by (auto simp add: quotient_of_inject)


subsubsection {* Various *}

lemma Fract_of_int_quotient: "Fract k l = of_int k / of_int l"
  by (simp add: Fract_of_int_eq [symmetric])

lemma Fract_add_one: "n \<noteq> 0 ==> Fract (m + n) n = Fract m n + 1"
  by (simp add: rat_number_expand)

lemma quotient_of_div:
  assumes r: "quotient_of r = (n,d)"
  shows "r = of_int n / of_int d"
proof -
  from theI'[OF quotient_of_unique[of r], unfolded r[unfolded quotient_of_def]]
  have "r = Fract n d" by simp
  thus ?thesis using Fract_of_int_quotient by simp
qed

subsubsection {* The ordered field of rational numbers *}

lift_definition positive :: "rat \<Rightarrow> bool"
  is "\<lambda>x. 0 < fst x * snd x"
proof (clarsimp)
  fix a b c d :: int
  assume "b \<noteq> 0" and "d \<noteq> 0" and "a * d = c * b"
  hence "a * d * b * d = c * b * b * d"
    by simp
  hence "a * b * d\<^sup>2 = c * d * b\<^sup>2"
    unfolding power2_eq_square by (simp add: mult_ac)
  hence "0 < a * b * d\<^sup>2 \<longleftrightarrow> 0 < c * d * b\<^sup>2"
    by simp
  thus "0 < a * b \<longleftrightarrow> 0 < c * d"
    using `b \<noteq> 0` and `d \<noteq> 0`
    by (simp add: zero_less_mult_iff)
qed

lemma positive_zero: "\<not> positive 0"
  by transfer simp

lemma positive_add:
  "positive x \<Longrightarrow> positive y \<Longrightarrow> positive (x + y)"
apply transfer
apply (simp add: zero_less_mult_iff)
apply (elim disjE, simp_all add: add_pos_pos add_neg_neg
  mult_pos_pos mult_pos_neg mult_neg_pos mult_neg_neg)
done

lemma positive_mult:
  "positive x \<Longrightarrow> positive y \<Longrightarrow> positive (x * y)"
by transfer (drule (1) mult_pos_pos, simp add: mult_ac)

lemma positive_minus:
  "\<not> positive x \<Longrightarrow> x \<noteq> 0 \<Longrightarrow> positive (- x)"
by transfer (force simp: neq_iff zero_less_mult_iff mult_less_0_iff)

instantiation rat :: linordered_field_inverse_zero
begin

definition
  "x < y \<longleftrightarrow> positive (y - x)"

definition
  "x \<le> (y::rat) \<longleftrightarrow> x < y \<or> x = y"

definition
  "abs (a::rat) = (if a < 0 then - a else a)"

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

instance proof
  fix a b c :: rat
  show "\<bar>a\<bar> = (if a < 0 then - a else a)"
    by (rule abs_rat_def)
  show "a < b \<longleftrightarrow> a \<le> b \<and> \<not> b \<le> a"
    unfolding less_eq_rat_def less_rat_def
    by (auto, drule (1) positive_add, simp_all add: positive_zero)
  show "a \<le> a"
    unfolding less_eq_rat_def by simp
  show "a \<le> b \<Longrightarrow> b \<le> c \<Longrightarrow> a \<le> c"
    unfolding less_eq_rat_def less_rat_def
    by (auto, drule (1) positive_add, simp add: algebra_simps)
  show "a \<le> b \<Longrightarrow> b \<le> a \<Longrightarrow> a = b"
    unfolding less_eq_rat_def less_rat_def
    by (auto, drule (1) positive_add, simp add: positive_zero)
  show "a \<le> b \<Longrightarrow> c + a \<le> c + b"
    unfolding less_eq_rat_def less_rat_def by (auto simp: diff_minus)
  show "sgn a = (if a = 0 then 0 else if 0 < a then 1 else - 1)"
    by (rule sgn_rat_def)
  show "a \<le> b \<or> b \<le> a"
    unfolding less_eq_rat_def less_rat_def
    by (auto dest!: positive_minus)
  show "a < b \<Longrightarrow> 0 < c \<Longrightarrow> c * a < c * b"
    unfolding less_rat_def
    by (drule (1) positive_mult, simp add: algebra_simps)
qed

end

instantiation rat :: distrib_lattice
begin

definition
  "(inf :: rat \<Rightarrow> rat \<Rightarrow> rat) = min"

definition
  "(sup :: rat \<Rightarrow> rat \<Rightarrow> rat) = max"

instance proof
qed (auto simp add: inf_rat_def sup_rat_def min_max.sup_inf_distrib1)

end

lemma positive_rat: "positive (Fract a b) \<longleftrightarrow> 0 < a * b"
  by transfer simp

lemma less_rat [simp]:
  assumes "b \<noteq> 0" and "d \<noteq> 0"
  shows "Fract a b < Fract c d \<longleftrightarrow> (a * d) * (b * d) < (c * b) * (b * d)"
  using assms unfolding less_rat_def
  by (simp add: positive_rat algebra_simps)

lemma le_rat [simp]:
  assumes "b \<noteq> 0" and "d \<noteq> 0"
  shows "Fract a b \<le> Fract c d \<longleftrightarrow> (a * d) * (b * d) \<le> (c * b) * (b * d)"
  using assms unfolding le_less by (simp add: eq_rat)

lemma abs_rat [simp, code]: "\<bar>Fract a b\<bar> = Fract \<bar>a\<bar> \<bar>b\<bar>"
  by (auto simp add: abs_rat_def zabs_def Zero_rat_def not_less le_less eq_rat zero_less_mult_iff)

lemma sgn_rat [simp, code]: "sgn (Fract a b) = of_int (sgn a * sgn b)"
  unfolding Fract_of_int_eq
  by (auto simp: zsgn_def sgn_rat_def Zero_rat_def eq_rat)
    (auto simp: rat_number_collapse not_less le_less zero_less_mult_iff)

lemma Rat_induct_pos [case_names Fract, induct type: rat]:
  assumes step: "\<And>a b. 0 < b \<Longrightarrow> P (Fract a b)"
  shows "P q"
proof (cases q)
  have step': "\<And>a b. b < 0 \<Longrightarrow> P (Fract a b)"
  proof -
    fix a::int and b::int
    assume b: "b < 0"
    hence "0 < -b" by simp
    hence "P (Fract (-a) (-b))" by (rule step)
    thus "P (Fract a b)" by (simp add: order_less_imp_not_eq [OF b])
  qed
  case (Fract a b)
  thus "P q" by (force simp add: linorder_neq_iff step step')
qed

lemma zero_less_Fract_iff:
  "0 < b \<Longrightarrow> 0 < Fract a b \<longleftrightarrow> 0 < a"
  by (simp add: Zero_rat_def zero_less_mult_iff)

lemma Fract_less_zero_iff:
  "0 < b \<Longrightarrow> Fract a b < 0 \<longleftrightarrow> a < 0"
  by (simp add: Zero_rat_def mult_less_0_iff)

lemma zero_le_Fract_iff:
  "0 < b \<Longrightarrow> 0 \<le> Fract a b \<longleftrightarrow> 0 \<le> a"
  by (simp add: Zero_rat_def zero_le_mult_iff)

lemma Fract_le_zero_iff:
  "0 < b \<Longrightarrow> Fract a b \<le> 0 \<longleftrightarrow> a \<le> 0"
  by (simp add: Zero_rat_def mult_le_0_iff)

lemma one_less_Fract_iff:
  "0 < b \<Longrightarrow> 1 < Fract a b \<longleftrightarrow> b < a"
  by (simp add: One_rat_def mult_less_cancel_right_disj)

lemma Fract_less_one_iff:
  "0 < b \<Longrightarrow> Fract a b < 1 \<longleftrightarrow> a < b"
  by (simp add: One_rat_def mult_less_cancel_right_disj)

lemma one_le_Fract_iff:
  "0 < b \<Longrightarrow> 1 \<le> Fract a b \<longleftrightarrow> b \<le> a"
  by (simp add: One_rat_def mult_le_cancel_right)

lemma Fract_le_one_iff:
  "0 < b \<Longrightarrow> Fract a b \<le> 1 \<longleftrightarrow> a \<le> b"
  by (simp add: One_rat_def mult_le_cancel_right)


subsubsection {* Rationals are an Archimedean field *}

lemma rat_floor_lemma:
  shows "of_int (a div b) \<le> Fract a b \<and> Fract a b < of_int (a div b + 1)"
proof -
  have "Fract a b = of_int (a div b) + Fract (a mod b) b"
    by (cases "b = 0", simp, simp add: of_int_rat)
  moreover have "0 \<le> Fract (a mod b) b \<and> Fract (a mod b) b < 1"
    unfolding Fract_of_int_quotient
    by (rule linorder_cases [of b 0]) (simp add: divide_nonpos_neg, simp, simp add: divide_nonneg_pos)
  ultimately show ?thesis by simp
qed

instance rat :: archimedean_field
proof
  fix r :: rat
  show "\<exists>z. r \<le> of_int z"
  proof (induct r)
    case (Fract a b)
    have "Fract a b \<le> of_int (a div b + 1)"
      using rat_floor_lemma [of a b] by simp
    then show "\<exists>z. Fract a b \<le> of_int z" ..
  qed
qed

instantiation rat :: floor_ceiling
begin

definition [code del]:
  "floor (x::rat) = (THE z. of_int z \<le> x \<and> x < of_int (z + 1))"

instance proof
  fix x :: rat
  show "of_int (floor x) \<le> x \<and> x < of_int (floor x + 1)"
    unfolding floor_rat_def using floor_exists1 by (rule theI')
qed

end

lemma floor_Fract: "floor (Fract a b) = a div b"
  using rat_floor_lemma [of a b]
  by (simp add: floor_unique)


subsection {* Linear arithmetic setup *}

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_int_eq_iff} RS iffD2]
    (* not needed because x < (y::int) can be rewritten as x + 1 <= y: of_int_less_iff RS iffD2 *)
  #> Lin_Arith.add_simps [@{thm neg_less_iff_less},
      @{thm True_implies_equals},
      read_instantiate @{context} [(("a", 0), "(numeral ?v)")] @{thm distrib_left},
      read_instantiate @{context} [(("a", 0), "(neg_numeral ?v)")] @{thm distrib_left},
      @{thm divide_1}, @{thm divide_zero_left},
      @{thm times_divide_eq_right}, @{thm times_divide_eq_left},
      @{thm minus_divide_left} RS sym, @{thm minus_divide_right} RS sym,
      @{thm of_int_minus}, @{thm of_int_diff},
      @{thm of_int_of_nat_eq}]
  #> Lin_Arith.add_simprocs Numeral_Simprocs.field_cancel_numeral_factors
  #> Lin_Arith.add_inj_const (@{const_name of_nat}, @{typ "nat => rat"})
  #> Lin_Arith.add_inj_const (@{const_name of_int}, @{typ "int => rat"}))
*}


subsection {* Embedding from Rationals to other Fields *}

class field_char_0 = field + ring_char_0

subclass (in linordered_field) field_char_0 ..

context field_char_0
begin

lift_definition of_rat :: "rat \<Rightarrow> 'a"
  is "\<lambda>x. of_int (fst x) / of_int (snd x)"
apply (clarsimp simp add: nonzero_divide_eq_eq nonzero_eq_divide_eq)
apply (simp only: of_int_mult [symmetric])
done

end

lemma of_rat_rat: "b \<noteq> 0 \<Longrightarrow> of_rat (Fract a b) = of_int a / of_int b"
  by transfer simp

lemma of_rat_0 [simp]: "of_rat 0 = 0"
  by transfer simp

lemma of_rat_1 [simp]: "of_rat 1 = 1"
  by transfer simp

lemma of_rat_add: "of_rat (a + b) = of_rat a + of_rat b"
  by transfer (simp add: add_frac_eq)

lemma of_rat_minus: "of_rat (- a) = - of_rat a"
  by transfer simp

lemma of_rat_diff: "of_rat (a - b) = of_rat a - of_rat b"
by (simp only: diff_minus of_rat_add of_rat_minus)

lemma of_rat_mult: "of_rat (a * b) = of_rat a * of_rat b"
apply transfer
apply (simp add: divide_inverse nonzero_inverse_mult_distrib mult_ac)
done

lemma nonzero_of_rat_inverse:
  "a \<noteq> 0 \<Longrightarrow> of_rat (inverse a) = inverse (of_rat a)"
apply (rule inverse_unique [symmetric])
apply (simp add: of_rat_mult [symmetric])
done

lemma of_rat_inverse:
  "(of_rat (inverse a)::'a::{field_char_0, field_inverse_zero}) =
   inverse (of_rat a)"
by (cases "a = 0", simp_all add: nonzero_of_rat_inverse)

lemma nonzero_of_rat_divide:
  "b \<noteq> 0 \<Longrightarrow> of_rat (a / b) = of_rat a / of_rat b"
by (simp add: divide_inverse of_rat_mult nonzero_of_rat_inverse)

lemma of_rat_divide:
  "(of_rat (a / b)::'a::{field_char_0, field_inverse_zero})
   = of_rat a / of_rat b"
by (cases "b = 0") (simp_all add: nonzero_of_rat_divide)

lemma of_rat_power:
  "(of_rat (a ^ n)::'a::field_char_0) = of_rat a ^ n"
by (induct n) (simp_all add: of_rat_mult)

lemma of_rat_eq_iff [simp]: "(of_rat a = of_rat b) = (a = b)"
apply transfer
apply (simp add: nonzero_divide_eq_eq nonzero_eq_divide_eq)
apply (simp only: of_int_mult [symmetric] of_int_eq_iff)
done

lemma of_rat_less:
  "(of_rat r :: 'a::linordered_field) < of_rat s \<longleftrightarrow> r < s"
proof (induct r, induct s)
  fix a b c d :: int
  assume not_zero: "b > 0" "d > 0"
  then have "b * d > 0" by (rule mult_pos_pos)
  have of_int_divide_less_eq:
    "(of_int a :: 'a) / of_int b < of_int c / of_int d
      \<longleftrightarrow> (of_int a :: 'a) * of_int d < of_int c * of_int b"
    using not_zero by (simp add: pos_less_divide_eq pos_divide_less_eq)
  show "(of_rat (Fract a b) :: 'a::linordered_field) < of_rat (Fract c d)
    \<longleftrightarrow> Fract a b < Fract c d"
    using not_zero `b * d > 0`
    by (simp add: of_rat_rat of_int_divide_less_eq of_int_mult [symmetric] del: of_int_mult)
qed

lemma of_rat_less_eq:
  "(of_rat r :: 'a::linordered_field) \<le> of_rat s \<longleftrightarrow> r \<le> s"
  unfolding le_less by (auto simp add: of_rat_less)

lemmas of_rat_eq_0_iff [simp] = of_rat_eq_iff [of _ 0, simplified]

lemma of_rat_eq_id [simp]: "of_rat = id"
proof
  fix a
  show "of_rat a = id a"
  by (induct a)
     (simp add: of_rat_rat Fract_of_int_eq [symmetric])
qed

text{*Collapse nested embeddings*}
lemma of_rat_of_nat_eq [simp]: "of_rat (of_nat n) = of_nat n"
by (induct n) (simp_all add: of_rat_add)

lemma of_rat_of_int_eq [simp]: "of_rat (of_int z) = of_int z"
by (cases z rule: int_diff_cases) (simp add: of_rat_diff)

lemma of_rat_numeral_eq [simp]:
  "of_rat (numeral w) = numeral w"
using of_rat_of_int_eq [of "numeral w"] by simp

lemma of_rat_neg_numeral_eq [simp]:
  "of_rat (neg_numeral w) = neg_numeral w"
using of_rat_of_int_eq [of "neg_numeral w"] by simp

lemmas zero_rat = Zero_rat_def
lemmas one_rat = One_rat_def

abbreviation
  rat_of_nat :: "nat \<Rightarrow> rat"
where
  "rat_of_nat \<equiv> of_nat"

abbreviation
  rat_of_int :: "int \<Rightarrow> rat"
where
  "rat_of_int \<equiv> of_int"

subsection {* The Set of Rational Numbers *}

context field_char_0
begin

definition
  Rats  :: "'a set" where
  "Rats = range of_rat"

notation (xsymbols)
  Rats  ("\<rat>")

end

lemma Rats_of_rat [simp]: "of_rat r \<in> Rats"
by (simp add: Rats_def)

lemma Rats_of_int [simp]: "of_int z \<in> Rats"
by (subst of_rat_of_int_eq [symmetric], rule Rats_of_rat)

lemma Rats_of_nat [simp]: "of_nat n \<in> Rats"
by (subst of_rat_of_nat_eq [symmetric], rule Rats_of_rat)

lemma Rats_number_of [simp]: "numeral w \<in> Rats"
by (subst of_rat_numeral_eq [symmetric], rule Rats_of_rat)

lemma Rats_neg_number_of [simp]: "neg_numeral w \<in> Rats"
by (subst of_rat_neg_numeral_eq [symmetric], rule Rats_of_rat)

lemma Rats_0 [simp]: "0 \<in> Rats"
apply (unfold Rats_def)
apply (rule range_eqI)
apply (rule of_rat_0 [symmetric])
done

lemma Rats_1 [simp]: "1 \<in> Rats"
apply (unfold Rats_def)
apply (rule range_eqI)
apply (rule of_rat_1 [symmetric])
done

lemma Rats_add [simp]: "\<lbrakk>a \<in> Rats; b \<in> Rats\<rbrakk> \<Longrightarrow> a + b \<in> Rats"
apply (auto simp add: Rats_def)
apply (rule range_eqI)
apply (rule of_rat_add [symmetric])
done

lemma Rats_minus [simp]: "a \<in> Rats \<Longrightarrow> - a \<in> Rats"
apply (auto simp add: Rats_def)
apply (rule range_eqI)
apply (rule of_rat_minus [symmetric])
done

lemma Rats_diff [simp]: "\<lbrakk>a \<in> Rats; b \<in> Rats\<rbrakk> \<Longrightarrow> a - b \<in> Rats"
apply (auto simp add: Rats_def)
apply (rule range_eqI)
apply (rule of_rat_diff [symmetric])
done

lemma Rats_mult [simp]: "\<lbrakk>a \<in> Rats; b \<in> Rats\<rbrakk> \<Longrightarrow> a * b \<in> Rats"
apply (auto simp add: Rats_def)
apply (rule range_eqI)
apply (rule of_rat_mult [symmetric])
done

lemma nonzero_Rats_inverse:
  fixes a :: "'a::field_char_0"
  shows "\<lbrakk>a \<in> Rats; a \<noteq> 0\<rbrakk> \<Longrightarrow> inverse a \<in> Rats"
apply (auto simp add: Rats_def)
apply (rule range_eqI)
apply (erule nonzero_of_rat_inverse [symmetric])
done

lemma Rats_inverse [simp]:
  fixes a :: "'a::{field_char_0, field_inverse_zero}"
  shows "a \<in> Rats \<Longrightarrow> inverse a \<in> Rats"
apply (auto simp add: Rats_def)
apply (rule range_eqI)
apply (rule of_rat_inverse [symmetric])
done

lemma nonzero_Rats_divide:
  fixes a b :: "'a::field_char_0"
  shows "\<lbrakk>a \<in> Rats; b \<in> Rats; b \<noteq> 0\<rbrakk> \<Longrightarrow> a / b \<in> Rats"
apply (auto simp add: Rats_def)
apply (rule range_eqI)
apply (erule nonzero_of_rat_divide [symmetric])
done

lemma Rats_divide [simp]:
  fixes a b :: "'a::{field_char_0, field_inverse_zero}"
  shows "\<lbrakk>a \<in> Rats; b \<in> Rats\<rbrakk> \<Longrightarrow> a / b \<in> Rats"
apply (auto simp add: Rats_def)
apply (rule range_eqI)
apply (rule of_rat_divide [symmetric])
done

lemma Rats_power [simp]:
  fixes a :: "'a::field_char_0"
  shows "a \<in> Rats \<Longrightarrow> a ^ n \<in> Rats"
apply (auto simp add: Rats_def)
apply (rule range_eqI)
apply (rule of_rat_power [symmetric])
done

lemma Rats_cases [cases set: Rats]:
  assumes "q \<in> \<rat>"
  obtains (of_rat) r where "q = of_rat r"
proof -
  from `q \<in> \<rat>` have "q \<in> range of_rat" unfolding Rats_def .
  then obtain r where "q = of_rat r" ..
  then show thesis ..
qed

lemma Rats_induct [case_names of_rat, induct set: Rats]:
  "q \<in> \<rat> \<Longrightarrow> (\<And>r. P (of_rat r)) \<Longrightarrow> P q"
  by (rule Rats_cases) auto


subsection {* Implementation of rational numbers as pairs of integers *}

text {* Formal constructor *}

definition Frct :: "int \<times> int \<Rightarrow> rat" where
  [simp]: "Frct p = Fract (fst p) (snd p)"

lemma [code abstype]:
  "Frct (quotient_of q) = q"
  by (cases q) (auto intro: quotient_of_eq)


text {* Numerals *}

declare quotient_of_Fract [code abstract]

definition of_int :: "int \<Rightarrow> rat"
where
  [code_abbrev]: "of_int = Int.of_int"
hide_const (open) of_int

lemma quotient_of_int [code abstract]:
  "quotient_of (Rat.of_int a) = (a, 1)"
  by (simp add: of_int_def of_int_rat quotient_of_Fract)

lemma [code_unfold]:
  "numeral k = Rat.of_int (numeral k)"
  by (simp add: Rat.of_int_def)

lemma [code_unfold]:
  "neg_numeral k = Rat.of_int (neg_numeral k)"
  by (simp add: Rat.of_int_def)

lemma Frct_code_post [code_post]:
  "Frct (0, a) = 0"
  "Frct (a, 0) = 0"
  "Frct (1, 1) = 1"
  "Frct (numeral k, 1) = numeral k"
  "Frct (neg_numeral k, 1) = neg_numeral k"
  "Frct (1, numeral k) = 1 / numeral k"
  "Frct (1, neg_numeral k) = 1 / neg_numeral k"
  "Frct (numeral k, numeral l) = numeral k / numeral l"
  "Frct (numeral k, neg_numeral l) = numeral k / neg_numeral l"
  "Frct (neg_numeral k, numeral l) = neg_numeral k / numeral l"
  "Frct (neg_numeral k, neg_numeral l) = neg_numeral k / neg_numeral l"
  by (simp_all add: Fract_of_int_quotient)


text {* Operations *}

lemma rat_zero_code [code abstract]:
  "quotient_of 0 = (0, 1)"
  by (simp add: Zero_rat_def quotient_of_Fract normalize_def)

lemma rat_one_code [code abstract]:
  "quotient_of 1 = (1, 1)"
  by (simp add: One_rat_def quotient_of_Fract normalize_def)

lemma rat_plus_code [code abstract]:
  "quotient_of (p + q) = (let (a, c) = quotient_of p; (b, d) = quotient_of q
     in normalize (a * d + b * c, c * d))"
  by (cases p, cases q) (simp add: quotient_of_Fract)

lemma rat_uminus_code [code abstract]:
  "quotient_of (- p) = (let (a, b) = quotient_of p in (- a, b))"
  by (cases p) (simp add: quotient_of_Fract)

lemma rat_minus_code [code abstract]:
  "quotient_of (p - q) = (let (a, c) = quotient_of p; (b, d) = quotient_of q
     in normalize (a * d - b * c, c * d))"
  by (cases p, cases q) (simp add: quotient_of_Fract)

lemma rat_times_code [code abstract]:
  "quotient_of (p * q) = (let (a, c) = quotient_of p; (b, d) = quotient_of q
     in normalize (a * b, c * d))"
  by (cases p, cases q) (simp add: quotient_of_Fract)

lemma rat_inverse_code [code abstract]:
  "quotient_of (inverse p) = (let (a, b) = quotient_of p
    in if a = 0 then (0, 1) else (sgn a * b, \<bar>a\<bar>))"
proof (cases p)
  case (Fract a b) then show ?thesis
    by (cases "0::int" a rule: linorder_cases) (simp_all add: quotient_of_Fract gcd_int.commute)
qed

lemma rat_divide_code [code abstract]:
  "quotient_of (p / q) = (let (a, c) = quotient_of p; (b, d) = quotient_of q
     in normalize (a * d, c * b))"
  by (cases p, cases q) (simp add: quotient_of_Fract)

lemma rat_abs_code [code abstract]:
  "quotient_of \<bar>p\<bar> = (let (a, b) = quotient_of p in (\<bar>a\<bar>, b))"
  by (cases p) (simp add: quotient_of_Fract)

lemma rat_sgn_code [code abstract]:
  "quotient_of (sgn p) = (sgn (fst (quotient_of p)), 1)"
proof (cases p)
  case (Fract a b) then show ?thesis
  by (cases "0::int" a rule: linorder_cases) (simp_all add: quotient_of_Fract)
qed

lemma rat_floor_code [code]:
  "floor p = (let (a, b) = quotient_of p in a div b)"
by (cases p) (simp add: quotient_of_Fract floor_Fract)

instantiation rat :: equal
begin

definition [code]:
  "HOL.equal a b \<longleftrightarrow> quotient_of a = quotient_of b"

instance proof
qed (simp add: equal_rat_def quotient_of_inject_eq)

lemma rat_eq_refl [code nbe]:
  "HOL.equal (r::rat) r \<longleftrightarrow> True"
  by (rule equal_refl)

end

lemma rat_less_eq_code [code]:
  "p \<le> q \<longleftrightarrow> (let (a, c) = quotient_of p; (b, d) = quotient_of q in a * d \<le> c * b)"
  by (cases p, cases q) (simp add: quotient_of_Fract mult.commute)

lemma rat_less_code [code]:
  "p < q \<longleftrightarrow> (let (a, c) = quotient_of p; (b, d) = quotient_of q in a * d < c * b)"
  by (cases p, cases q) (simp add: quotient_of_Fract mult.commute)

lemma [code]:
  "of_rat p = (let (a, b) = quotient_of p in of_int a / of_int b)"
  by (cases p) (simp add: quotient_of_Fract of_rat_rat)


text {* Quickcheck *}

definition (in term_syntax)
  valterm_fract :: "int \<times> (unit \<Rightarrow> Code_Evaluation.term) \<Rightarrow> int \<times> (unit \<Rightarrow> Code_Evaluation.term) \<Rightarrow> rat \<times> (unit \<Rightarrow> Code_Evaluation.term)" where
  [code_unfold]: "valterm_fract k l = Code_Evaluation.valtermify Fract {\<cdot>} k {\<cdot>} l"

notation fcomp (infixl "\<circ>>" 60)
notation scomp (infixl "\<circ>\<rightarrow>" 60)

instantiation rat :: random
begin

definition
  "Quickcheck_Random.random i = Quickcheck_Random.random i \<circ>\<rightarrow> (\<lambda>num. Random.range i \<circ>\<rightarrow> (\<lambda>denom. Pair (
     let j = int_of_integer (integer_of_natural (denom + 1))
     in valterm_fract num (j, \<lambda>u. Code_Evaluation.term_of j))))"

instance ..

end

no_notation fcomp (infixl "\<circ>>" 60)
no_notation scomp (infixl "\<circ>\<rightarrow>" 60)

instantiation rat :: exhaustive
begin

definition
  "exhaustive_rat f d = Quickcheck_Exhaustive.exhaustive
    (\<lambda>l. Quickcheck_Exhaustive.exhaustive (\<lambda>k. f (Fract k (int_of_integer (integer_of_natural l) + 1))) d) d"

instance ..

end

instantiation rat :: full_exhaustive
begin

definition
  "full_exhaustive_rat f d = Quickcheck_Exhaustive.full_exhaustive (%(l, _). Quickcheck_Exhaustive.full_exhaustive (%k.
     f (let j = int_of_integer (integer_of_natural l) + 1
        in valterm_fract k (j, %_. Code_Evaluation.term_of j))) d) d"

instance ..

end

instantiation rat :: partial_term_of
begin

instance ..

end

lemma [code]:
  "partial_term_of (ty :: rat itself) (Quickcheck_Narrowing.Narrowing_variable p tt) == Code_Evaluation.Free (STR ''_'') (Typerep.Typerep (STR ''Rat.rat'') [])"
  "partial_term_of (ty :: rat itself) (Quickcheck_Narrowing.Narrowing_constructor 0 [l, k]) ==
     Code_Evaluation.App (Code_Evaluation.Const (STR ''Rat.Frct'')
     (Typerep.Typerep (STR ''fun'') [Typerep.Typerep (STR ''Product_Type.prod'') [Typerep.Typerep (STR ''Int.int'') [], Typerep.Typerep (STR ''Int.int'') []],
        Typerep.Typerep (STR ''Rat.rat'') []])) (Code_Evaluation.App (Code_Evaluation.App (Code_Evaluation.Const (STR ''Product_Type.Pair'') (Typerep.Typerep (STR ''fun'') [Typerep.Typerep (STR ''Int.int'') [], Typerep.Typerep (STR ''fun'') [Typerep.Typerep (STR ''Int.int'') [], Typerep.Typerep (STR ''Product_Type.prod'') [Typerep.Typerep (STR ''Int.int'') [], Typerep.Typerep (STR ''Int.int'') []]]])) (partial_term_of (TYPE(int)) l)) (partial_term_of (TYPE(int)) k))"
by (rule partial_term_of_anything)+

instantiation rat :: narrowing
begin

definition
  "narrowing = Quickcheck_Narrowing.apply (Quickcheck_Narrowing.apply
    (Quickcheck_Narrowing.cons (%nom denom. Fract nom denom)) narrowing) narrowing"

instance ..

end


subsection {* Setup for Nitpick *}

declaration {*
  Nitpick_HOL.register_frac_type @{type_name rat}
   [(@{const_name zero_rat_inst.zero_rat}, @{const_name Nitpick.zero_frac}),
    (@{const_name one_rat_inst.one_rat}, @{const_name Nitpick.one_frac}),
    (@{const_name plus_rat_inst.plus_rat}, @{const_name Nitpick.plus_frac}),
    (@{const_name times_rat_inst.times_rat}, @{const_name Nitpick.times_frac}),
    (@{const_name uminus_rat_inst.uminus_rat}, @{const_name Nitpick.uminus_frac}),
    (@{const_name inverse_rat_inst.inverse_rat}, @{const_name Nitpick.inverse_frac}),
    (@{const_name ord_rat_inst.less_rat}, @{const_name Nitpick.less_frac}),
    (@{const_name ord_rat_inst.less_eq_rat}, @{const_name Nitpick.less_eq_frac}),
    (@{const_name field_char_0_class.of_rat}, @{const_name Nitpick.of_frac})]
*}

lemmas [nitpick_unfold] = inverse_rat_inst.inverse_rat
  one_rat_inst.one_rat ord_rat_inst.less_rat
  ord_rat_inst.less_eq_rat plus_rat_inst.plus_rat times_rat_inst.times_rat
  uminus_rat_inst.uminus_rat zero_rat_inst.zero_rat


subsection {* Float syntax *}

syntax "_Float" :: "float_const \<Rightarrow> 'a"    ("_")

parse_translation {*
  let
    fun mk_number i =
      let
        fun mk 1 = Syntax.const @{const_syntax Num.One}
          | mk i =
              let val (q, r) = Integer.div_mod i 2
              in HOLogic.mk_bit r $ (mk q) end;
      in
        if i = 0 then Syntax.const @{const_syntax Groups.zero}
        else if i > 0 then Syntax.const @{const_syntax Num.numeral} $ mk i
        else Syntax.const @{const_syntax Num.neg_numeral} $ mk (~i)
      end;

    fun mk_frac str =
      let
        val {mant = i, exp = n} = Lexicon.read_float str;
        val exp = Syntax.const @{const_syntax Power.power};
        val ten = mk_number 10;
        val exp10 = if n = 1 then ten else exp $ ten $ mk_number n;
      in Syntax.const @{const_syntax divide} $ mk_number i $ exp10 end;

    fun float_tr [(c as Const (@{syntax_const "_constrain"}, _)) $ t $ u] = c $ float_tr [t] $ u
      | float_tr [t as Const (str, _)] = mk_frac str
      | float_tr ts = raise TERM ("float_tr", ts);
  in [(@{syntax_const "_Float"}, K float_tr)] end
*}

text{* Test: *}
lemma "123.456 = -111.111 + 200 + 30 + 4 + 5/10 + 6/100 + (7/1000::rat)"
  by simp


hide_const (open) normalize positive

lemmas [transfer_rule del] =
  rat.rel_eq_transfer
  Fract.transfer zero_rat.transfer one_rat.transfer plus_rat.transfer
  uminus_rat.transfer times_rat.transfer inverse_rat.transfer
  positive.transfer of_rat.transfer rat.right_unique rat.right_total

lemmas [transfer_domain_rule del] = Domainp_cr_rat rat.domain

text {* De-register @{text "rat"} as a quotient type: *}

declare Quotient_rat[quot_del]

end