Theory Nat

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theory Nat
imports Inductive Ring_and_Field
uses ($ISABELLE_HOME/src/Tools/rat.ML) ($ISABELLE_HOME/src/Provers/Arith/cancel_sums.ML) arith_data.ML ($ISABELLE_HOME/src/Provers/Arith/fast_lin_arith.ML) Tools/lin_arith.ML
begin

(*  Title:      HOL/Nat.thy
    ID:         $Id: Nat.thy,v 1.138 2008/04/25 13:30:34 krauss Exp $
    Author:     Tobias Nipkow and Lawrence C Paulson and Markus Wenzel

Type "nat" is a linear order, and a datatype; arithmetic operators + -
and * (for div, mod and dvd, see theory Divides).
*)

header {* Natural numbers *}

theory Nat
imports Inductive Ring_and_Field
uses
  "~~/src/Tools/rat.ML"
  "~~/src/Provers/Arith/cancel_sums.ML"
  ("arith_data.ML")
  "~~/src/Provers/Arith/fast_lin_arith.ML"
  ("Tools/lin_arith.ML")
begin

subsection {* Type @{text ind} *}

typedecl ind

axiomatization
  Zero_Rep :: ind and
  Suc_Rep :: "ind => ind"
where
  -- {* the axiom of infinity in 2 parts *}
  inj_Suc_Rep:          "inj Suc_Rep" and
  Suc_Rep_not_Zero_Rep: "Suc_Rep x ≠ Zero_Rep"


subsection {* Type nat *}

text {* Type definition *}

inductive Nat :: "ind => bool"
where
    Zero_RepI: "Nat Zero_Rep"
  | Suc_RepI: "Nat i ==> Nat (Suc_Rep i)"

global

typedef (open Nat)
  nat = "Collect Nat"
  by (rule exI, rule CollectI, rule Nat.Zero_RepI)

constdefs
  Suc :: "nat => nat"
  Suc_def:      "Suc == (%n. Abs_Nat (Suc_Rep (Rep_Nat n)))"

local

instantiation nat :: zero
begin

definition Zero_nat_def [code func del]:
  "0 = Abs_Nat Zero_Rep"

instance ..

end

lemma nat_induct: "P 0 ==> (!!n. P n ==> P (Suc n)) ==> P n"
  apply (unfold Zero_nat_def Suc_def)
  apply (rule Rep_Nat_inverse [THEN subst]) -- {* types force good instantiation *}
  apply (erule Rep_Nat [THEN CollectD, THEN Nat.induct])
  apply (iprover elim: Abs_Nat_inverse [OF CollectI, THEN subst])
  done

lemma Suc_not_Zero [iff]: "Suc m ≠ 0"
  by (simp add: Zero_nat_def Suc_def
    Abs_Nat_inject Rep_Nat [THEN CollectD] Suc_RepI Zero_RepI
      Suc_Rep_not_Zero_Rep)

lemma Zero_not_Suc [iff]: "0 ≠ Suc m"
  by (rule not_sym, rule Suc_not_Zero not_sym)

lemma inj_Suc[simp]: "inj_on Suc N"
  by (simp add: Suc_def inj_on_def Abs_Nat_inject Rep_Nat [THEN CollectD] Suc_RepI
                inj_Suc_Rep [THEN inj_eq] Rep_Nat_inject)

lemma Suc_Suc_eq [iff]: "Suc m = Suc n <-> m = n"
  by (rule inj_Suc [THEN inj_eq])

rep_datatype nat
  distinct  Suc_not_Zero Zero_not_Suc
  inject    Suc_Suc_eq
  induction nat_induct

declare nat.induct [case_names 0 Suc, induct type: nat]
declare nat.exhaust [case_names 0 Suc, cases type: nat]

lemmas nat_rec_0 = nat.recs(1)
  and nat_rec_Suc = nat.recs(2)

lemmas nat_case_0 = nat.cases(1)
  and nat_case_Suc = nat.cases(2)


text {* Injectiveness and distinctness lemmas *}

lemma Suc_neq_Zero: "Suc m = 0 ==> R"
by (rule notE, rule Suc_not_Zero)

lemma Zero_neq_Suc: "0 = Suc m ==> R"
by (rule Suc_neq_Zero, erule sym)

lemma Suc_inject: "Suc x = Suc y ==> x = y"
by (rule inj_Suc [THEN injD])

lemma n_not_Suc_n: "n ≠ Suc n"
by (induct n) simp_all

lemma Suc_n_not_n: "Suc n ≠ n"
by (rule not_sym, rule n_not_Suc_n)

text {* A special form of induction for reasoning
  about @{term "m < n"} and @{term "m - n"} *}

lemma diff_induct: "(!!x. P x 0) ==> (!!y. P 0 (Suc y)) ==>
    (!!x y. P x y ==> P (Suc x) (Suc y)) ==> P m n"
  apply (rule_tac x = m in spec)
  apply (induct n)
  prefer 2
  apply (rule allI)
  apply (induct_tac x, iprover+)
  done


subsection {* Arithmetic operators *}

instantiation nat :: "{minus, comm_monoid_add}"
begin

primrec plus_nat
where
  add_0:      "0 + n = (n::nat)"
  | add_Suc:  "Suc m + n = Suc (m + n)"

lemma add_0_right [simp]: "m + 0 = (m::nat)"
  by (induct m) simp_all

lemma add_Suc_right [simp]: "m + Suc n = Suc (m + n)"
  by (induct m) simp_all

lemma add_Suc_shift [code]: "Suc m + n = m + Suc n"
  by simp

primrec minus_nat
where
  diff_0:     "m - 0 = (m::nat)"
  | diff_Suc: "m - Suc n = (case m - n of 0 => 0 | Suc k => k)"

declare diff_Suc [simp del, code del]

lemma diff_0_eq_0 [simp, code]: "0 - n = (0::nat)"
  by (induct n) (simp_all add: diff_Suc)

lemma diff_Suc_Suc [simp, code]: "Suc m - Suc n = m - n"
  by (induct n) (simp_all add: diff_Suc)

instance proof
  fix n m q :: nat
  show "(n + m) + q = n + (m + q)" by (induct n) simp_all
  show "n + m = m + n" by (induct n) simp_all
  show "0 + n = n" by simp
qed

end

instantiation nat :: comm_semiring_1_cancel
begin

definition
  One_nat_def [simp]: "1 = Suc 0"

primrec times_nat
where
  mult_0:     "0 * n = (0::nat)"
  | mult_Suc: "Suc m * n = n + (m * n)"

lemma mult_0_right [simp]: "(m::nat) * 0 = 0"
  by (induct m) simp_all

lemma mult_Suc_right [simp]: "m * Suc n = m + (m * n)"
  by (induct m) (simp_all add: add_left_commute)

lemma add_mult_distrib: "(m + n) * k = (m * k) + ((n * k)::nat)"
  by (induct m) (simp_all add: add_assoc)

instance proof
  fix n m q :: nat
  show "0 ≠ (1::nat)" by simp
  show "1 * n = n" by simp
  show "n * m = m * n" by (induct n) simp_all
  show "(n * m) * q = n * (m * q)" by (induct n) (simp_all add: add_mult_distrib)
  show "(n + m) * q = n * q + m * q" by (rule add_mult_distrib)
  assume "n + m = n + q" thus "m = q" by (induct n) simp_all
qed

end

subsubsection {* Addition *}

lemma nat_add_assoc: "(m + n) + k = m + ((n + k)::nat)"
  by (rule add_assoc)

lemma nat_add_commute: "m + n = n + (m::nat)"
  by (rule add_commute)

lemma nat_add_left_commute: "x + (y + z) = y + ((x + z)::nat)"
  by (rule add_left_commute)

lemma nat_add_left_cancel [simp]: "(k + m = k + n) = (m = (n::nat))"
  by (rule add_left_cancel)

lemma nat_add_right_cancel [simp]: "(m + k = n + k) = (m=(n::nat))"
  by (rule add_right_cancel)

text {* Reasoning about @{text "m + 0 = 0"}, etc. *}

lemma add_is_0 [iff]:
  fixes m n :: nat
  shows "(m + n = 0) = (m = 0 & n = 0)"
  by (cases m) simp_all

lemma add_is_1:
  "(m+n= Suc 0) = (m= Suc 0 & n=0 | m=0 & n= Suc 0)"
  by (cases m) simp_all

lemma one_is_add:
  "(Suc 0 = m + n) = (m = Suc 0 & n = 0 | m = 0 & n = Suc 0)"
  by (rule trans, rule eq_commute, rule add_is_1)

lemma add_eq_self_zero:
  fixes m n :: nat
  shows "m + n = m ==> n = 0"
  by (induct m) simp_all

lemma inj_on_add_nat[simp]: "inj_on (%n::nat. n+k) N"
  apply (induct k)
   apply simp
  apply(drule comp_inj_on[OF _ inj_Suc])
  apply (simp add:o_def)
  done


subsubsection {* Difference *}

lemma diff_self_eq_0 [simp]: "(m::nat) - m = 0"
  by (induct m) simp_all

lemma diff_diff_left: "(i::nat) - j - k = i - (j + k)"
  by (induct i j rule: diff_induct) simp_all

lemma Suc_diff_diff [simp]: "(Suc m - n) - Suc k = m - n - k"
  by (simp add: diff_diff_left)

lemma diff_commute: "(i::nat) - j - k = i - k - j"
  by (simp add: diff_diff_left add_commute)

lemma diff_add_inverse: "(n + m) - n = (m::nat)"
  by (induct n) simp_all

lemma diff_add_inverse2: "(m + n) - n = (m::nat)"
  by (simp add: diff_add_inverse add_commute [of m n])

lemma diff_cancel: "(k + m) - (k + n) = m - (n::nat)"
  by (induct k) simp_all

lemma diff_cancel2: "(m + k) - (n + k) = m - (n::nat)"
  by (simp add: diff_cancel add_commute)

lemma diff_add_0: "n - (n + m) = (0::nat)"
  by (induct n) simp_all

text {* Difference distributes over multiplication *}

lemma diff_mult_distrib: "((m::nat) - n) * k = (m * k) - (n * k)"
by (induct m n rule: diff_induct) (simp_all add: diff_cancel)

lemma diff_mult_distrib2: "k * ((m::nat) - n) = (k * m) - (k * n)"
by (simp add: diff_mult_distrib mult_commute [of k])
  -- {* NOT added as rewrites, since sometimes they are used from right-to-left *}


subsubsection {* Multiplication *}

lemma nat_mult_assoc: "(m * n) * k = m * ((n * k)::nat)"
  by (rule mult_assoc)

lemma nat_mult_commute: "m * n = n * (m::nat)"
  by (rule mult_commute)

lemma add_mult_distrib2: "k * (m + n) = (k * m) + ((k * n)::nat)"
  by (rule right_distrib)

lemma mult_is_0 [simp]: "((m::nat) * n = 0) = (m=0 | n=0)"
  by (induct m) auto

lemmas nat_distrib =
  add_mult_distrib add_mult_distrib2 diff_mult_distrib diff_mult_distrib2

lemma mult_eq_1_iff [simp]: "(m * n = Suc 0) = (m = 1 & n = 1)"
  apply (induct m)
   apply simp
  apply (induct n)
   apply auto
  done

lemma one_eq_mult_iff [simp,noatp]: "(Suc 0 = m * n) = (m = 1 & n = 1)"
  apply (rule trans)
  apply (rule_tac [2] mult_eq_1_iff, fastsimp)
  done

lemma mult_cancel1 [simp]: "(k * m = k * n) = (m = n | (k = (0::nat)))"
proof -
  have "k ≠ 0 ==> k * m = k * n ==> m = n"
  proof (induct n arbitrary: m)
    case 0 then show "m = 0" by simp
  next
    case (Suc n) then show "m = Suc n"
      by (cases m) (simp_all add: eq_commute [of "0"])
  qed
  then show ?thesis by auto
qed

lemma mult_cancel2 [simp]: "(m * k = n * k) = (m = n | (k = (0::nat)))"
  by (simp add: mult_commute)

lemma Suc_mult_cancel1: "(Suc k * m = Suc k * n) = (m = n)"
  by (subst mult_cancel1) simp


subsection {* Orders on @{typ nat} *}

subsubsection {* Operation definition *}

instantiation nat :: linorder
begin

primrec less_eq_nat where
  "(0::nat) ≤ n <-> True"
  | "Suc m ≤ n <-> (case n of 0 => False | Suc n => m ≤ n)"

declare less_eq_nat.simps [simp del, code del]
lemma [code]: "(0::nat) ≤ n <-> True" by (simp add: less_eq_nat.simps)
lemma le0 [iff]: "0 ≤ (n::nat)" by (simp add: less_eq_nat.simps)

definition less_nat where
  less_eq_Suc_le [code func del]: "n < m <-> Suc n ≤ m"

lemma Suc_le_mono [iff]: "Suc n ≤ Suc m <-> n ≤ m"
  by (simp add: less_eq_nat.simps(2))

lemma Suc_le_eq [code]: "Suc m ≤ n <-> m < n"
  unfolding less_eq_Suc_le ..

lemma le_0_eq [iff]: "(n::nat) ≤ 0 <-> n = 0"
  by (induct n) (simp_all add: less_eq_nat.simps(2))

lemma not_less0 [iff]: "¬ n < (0::nat)"
  by (simp add: less_eq_Suc_le)

lemma less_nat_zero_code [code]: "n < (0::nat) <-> False"
  by simp

lemma Suc_less_eq [iff]: "Suc m < Suc n <-> m < n"
  by (simp add: less_eq_Suc_le)

lemma less_Suc_eq_le [code]: "m < Suc n <-> m ≤ n"
  by (simp add: less_eq_Suc_le)

lemma le_SucI: "m ≤ n ==> m ≤ Suc n"
  by (induct m arbitrary: n)
    (simp_all add: less_eq_nat.simps(2) split: nat.splits)

lemma Suc_leD: "Suc m ≤ n ==> m ≤ n"
  by (cases n) (auto intro: le_SucI)

lemma less_SucI: "m < n ==> m < Suc n"
  by (simp add: less_eq_Suc_le) (erule Suc_leD)

lemma Suc_lessD: "Suc m < n ==> m < n"
  by (simp add: less_eq_Suc_le) (erule Suc_leD)

instance
proof
  fix n m :: nat
  have less_imp_le: "n < m ==> n ≤ m"
    unfolding less_eq_Suc_le by (erule Suc_leD)
  have irrefl: "¬ m < m" by (induct m) auto
  have strict: "n ≤ m ==> n ≠ m ==> n < m"
  proof (induct n arbitrary: m)
    case 0 then show ?case
      by (cases m) (simp_all add: less_eq_Suc_le)
  next
    case (Suc n) then show ?case
      by (cases m) (simp_all add: less_eq_Suc_le)
  qed
  show "n < m <-> n ≤ m ∧ n ≠ m"
    by (auto simp add: irrefl intro: less_imp_le strict)
next
  fix n :: nat show "n ≤ n" by (induct n) simp_all
next
  fix n m :: nat assume "n ≤ m" and "m ≤ n"
  then show "n = m"
    by (induct n arbitrary: m)
      (simp_all add: less_eq_nat.simps(2) split: nat.splits)
next
  fix n m q :: nat assume "n ≤ m" and "m ≤ q"
  then show "n ≤ q"
  proof (induct n arbitrary: m q)
    case 0 show ?case by simp
  next
    case (Suc n) then show ?case
      by (simp_all (no_asm_use) add: less_eq_nat.simps(2) split: nat.splits, clarify,
        simp_all (no_asm_use) add: less_eq_nat.simps(2) split: nat.splits, clarify,
        simp_all (no_asm_use) add: less_eq_nat.simps(2) split: nat.splits)
  qed
next
  fix n m :: nat show "n ≤ m ∨ m ≤ n"
    by (induct n arbitrary: m)
      (simp_all add: less_eq_nat.simps(2) split: nat.splits)
qed

end

subsubsection {* Introduction properties *}

lemma lessI [iff]: "n < Suc n"
  by (simp add: less_Suc_eq_le)

lemma zero_less_Suc [iff]: "0 < Suc n"
  by (simp add: less_Suc_eq_le)


subsubsection {* Elimination properties *}

lemma less_not_refl: "~ n < (n::nat)"
  by (rule order_less_irrefl)

lemma less_not_refl2: "n < m ==> m ≠ (n::nat)"
  by (rule not_sym) (rule less_imp_neq) 

lemma less_not_refl3: "(s::nat) < t ==> s ≠ t"
  by (rule less_imp_neq)

lemma less_irrefl_nat: "(n::nat) < n ==> R"
  by (rule notE, rule less_not_refl)

lemma less_zeroE: "(n::nat) < 0 ==> R"
  by (rule notE) (rule not_less0)

lemma less_Suc_eq: "(m < Suc n) = (m < n | m = n)"
  unfolding less_Suc_eq_le le_less ..

lemma less_one [iff, noatp]: "(n < (1::nat)) = (n = 0)"
  by (simp add: less_Suc_eq)

lemma less_Suc0 [iff]: "(n < Suc 0) = (n = 0)"
  by (simp add: less_Suc_eq)

lemma Suc_mono: "m < n ==> Suc m < Suc n"
  by simp

text {* "Less than" is antisymmetric, sort of *}
lemma less_antisym: "[| ¬ n < m; n < Suc m |] ==> m = n"
  unfolding not_less less_Suc_eq_le by (rule antisym)

lemma nat_neq_iff: "((m::nat) ≠ n) = (m < n | n < m)"
  by (rule linorder_neq_iff)

lemma nat_less_cases: assumes major: "(m::nat) < n ==> P n m"
  and eqCase: "m = n ==> P n m" and lessCase: "n<m ==> P n m"
  shows "P n m"
  apply (rule less_linear [THEN disjE])
  apply (erule_tac [2] disjE)
  apply (erule lessCase)
  apply (erule sym [THEN eqCase])
  apply (erule major)
  done


subsubsection {* Inductive (?) properties *}

lemma Suc_lessI: "m < n ==> Suc m ≠ n ==> Suc m < n"
  unfolding less_eq_Suc_le [of m] le_less by simp 

lemma lessE:
  assumes major: "i < k"
  and p1: "k = Suc i ==> P" and p2: "!!j. i < j ==> k = Suc j ==> P"
  shows P
proof -
  from major have "∃j. i ≤ j ∧ k = Suc j"
    unfolding less_eq_Suc_le by (induct k) simp_all
  then have "(∃j. i < j ∧ k = Suc j) ∨ k = Suc i"
    by (clarsimp simp add: less_le)
  with p1 p2 show P by auto
qed

lemma less_SucE: assumes major: "m < Suc n"
  and less: "m < n ==> P" and eq: "m = n ==> P" shows P
  apply (rule major [THEN lessE])
  apply (rule eq, blast)
  apply (rule less, blast)
  done

lemma Suc_lessE: assumes major: "Suc i < k"
  and minor: "!!j. i < j ==> k = Suc j ==> P" shows P
  apply (rule major [THEN lessE])
  apply (erule lessI [THEN minor])
  apply (erule Suc_lessD [THEN minor], assumption)
  done

lemma Suc_less_SucD: "Suc m < Suc n ==> m < n"
  by simp

lemma less_trans_Suc:
  assumes le: "i < j" shows "j < k ==> Suc i < k"
  apply (induct k, simp_all)
  apply (insert le)
  apply (simp add: less_Suc_eq)
  apply (blast dest: Suc_lessD)
  done

text {* Can be used with @{text less_Suc_eq} to get @{term "n = m | n < m"} *}
lemma not_less_eq: "¬ m < n <-> n < Suc m"
  unfolding not_less less_Suc_eq_le ..

lemma not_less_eq_eq: "¬ m ≤ n <-> Suc n ≤ m"
  unfolding not_le Suc_le_eq ..

text {* Properties of "less than or equal" *}

lemma le_imp_less_Suc: "m ≤ n ==> m < Suc n"
  unfolding less_Suc_eq_le .

lemma Suc_n_not_le_n: "~ Suc n ≤ n"
  unfolding not_le less_Suc_eq_le ..

lemma le_Suc_eq: "(m ≤ Suc n) = (m ≤ n | m = Suc n)"
  by (simp add: less_Suc_eq_le [symmetric] less_Suc_eq)

lemma le_SucE: "m ≤ Suc n ==> (m ≤ n ==> R) ==> (m = Suc n ==> R) ==> R"
  by (drule le_Suc_eq [THEN iffD1], iprover+)

lemma Suc_leI: "m < n ==> Suc(m) ≤ n"
  unfolding Suc_le_eq .

text {* Stronger version of @{text Suc_leD} *}
lemma Suc_le_lessD: "Suc m ≤ n ==> m < n"
  unfolding Suc_le_eq .

lemma less_imp_le_nat: "m < n ==> m ≤ (n::nat)"
  unfolding less_eq_Suc_le by (rule Suc_leD)

text {* For instance, @{text "(Suc m < Suc n) = (Suc m ≤ n) = (m < n)"} *}
lemmas le_simps = less_imp_le_nat less_Suc_eq_le Suc_le_eq


text {* Equivalence of @{term "m ≤ n"} and @{term "m < n | m = n"} *}

lemma less_or_eq_imp_le: "m < n | m = n ==> m ≤ (n::nat)"
  unfolding le_less .

lemma le_eq_less_or_eq: "(m ≤ (n::nat)) = (m < n | m=n)"
  by (rule le_less)

text {* Useful with @{text blast}. *}
lemma eq_imp_le: "(m::nat) = n ==> m ≤ n"
  by auto

lemma le_refl: "n ≤ (n::nat)"
  by simp

lemma le_trans: "[| i ≤ j; j ≤ k |] ==> i ≤ (k::nat)"
  by (rule order_trans)

lemma le_anti_sym: "[| m ≤ n; n ≤ m |] ==> m = (n::nat)"
  by (rule antisym)

lemma nat_less_le: "((m::nat) < n) = (m ≤ n & m ≠ n)"
  by (rule less_le)

lemma le_neq_implies_less: "(m::nat) ≤ n ==> m ≠ n ==> m < n"
  unfolding less_le ..

lemma nat_le_linear: "(m::nat) ≤ n | n ≤ m"
  by (rule linear)

lemmas linorder_neqE_nat = linorder_neqE [where 'a = nat]

lemma le_less_Suc_eq: "m ≤ n ==> (n < Suc m) = (n = m)"
  unfolding less_Suc_eq_le by auto

lemma not_less_less_Suc_eq: "~ n < m ==> (n < Suc m) = (n = m)"
  unfolding not_less by (rule le_less_Suc_eq)

lemmas not_less_simps = not_less_less_Suc_eq le_less_Suc_eq

text {* These two rules ease the use of primitive recursion.
NOTE USE OF @{text "=="} *}
lemma def_nat_rec_0: "(!!n. f n == nat_rec c h n) ==> f 0 = c"
by simp

lemma def_nat_rec_Suc: "(!!n. f n == nat_rec c h n) ==> f (Suc n) = h n (f n)"
by simp

lemma not0_implies_Suc: "n ≠ 0 ==> ∃m. n = Suc m"
by (cases n) simp_all

lemma gr0_implies_Suc: "n > 0 ==> ∃m. n = Suc m"
by (cases n) simp_all

lemma gr_implies_not0: fixes n :: nat shows "m<n ==> n ≠ 0"
by (cases n) simp_all

lemma neq0_conv[iff]: fixes n :: nat shows "(n ≠ 0) = (0 < n)"
by (cases n) simp_all

text {* This theorem is useful with @{text blast} *}
lemma gr0I: "((n::nat) = 0 ==> False) ==> 0 < n"
by (rule neq0_conv[THEN iffD1], iprover)

lemma gr0_conv_Suc: "(0 < n) = (∃m. n = Suc m)"
by (fast intro: not0_implies_Suc)

lemma not_gr0 [iff,noatp]: "!!n::nat. (~ (0 < n)) = (n = 0)"
using neq0_conv by blast

lemma Suc_le_D: "(Suc n ≤ m') ==> (? m. m' = Suc m)"
by (induct m') simp_all

text {* Useful in certain inductive arguments *}
lemma less_Suc_eq_0_disj: "(m < Suc n) = (m = 0 | (∃j. m = Suc j & j < n))"
by (cases m) simp_all


subsubsection {* @{term min} and @{term max} *}

lemma mono_Suc: "mono Suc"
by (rule monoI) simp

lemma min_0L [simp]: "min 0 n = (0::nat)"
by (rule min_leastL) simp

lemma min_0R [simp]: "min n 0 = (0::nat)"
by (rule min_leastR) simp

lemma min_Suc_Suc [simp]: "min (Suc m) (Suc n) = Suc (min m n)"
by (simp add: mono_Suc min_of_mono)

lemma min_Suc1:
   "min (Suc n) m = (case m of 0 => 0 | Suc m' => Suc(min n m'))"
by (simp split: nat.split)

lemma min_Suc2:
   "min m (Suc n) = (case m of 0 => 0 | Suc m' => Suc(min m' n))"
by (simp split: nat.split)

lemma max_0L [simp]: "max 0 n = (n::nat)"
by (rule max_leastL) simp

lemma max_0R [simp]: "max n 0 = (n::nat)"
by (rule max_leastR) simp

lemma max_Suc_Suc [simp]: "max (Suc m) (Suc n) = Suc(max m n)"
by (simp add: mono_Suc max_of_mono)

lemma max_Suc1:
   "max (Suc n) m = (case m of 0 => Suc n | Suc m' => Suc(max n m'))"
by (simp split: nat.split)

lemma max_Suc2:
   "max m (Suc n) = (case m of 0 => Suc n | Suc m' => Suc(max m' n))"
by (simp split: nat.split)


subsubsection {* Monotonicity of Addition *}

lemma Suc_pred [simp]: "n>0 ==> Suc (n - Suc 0) = n"
by (simp add: diff_Suc split: nat.split)

lemma nat_add_left_cancel_le [simp]: "(k + m ≤ k + n) = (m≤(n::nat))"
by (induct k) simp_all

lemma nat_add_left_cancel_less [simp]: "(k + m < k + n) = (m<(n::nat))"
by (induct k) simp_all

lemma add_gr_0 [iff]: "!!m::nat. (m + n > 0) = (m>0 | n>0)"
by(auto dest:gr0_implies_Suc)

text {* strict, in 1st argument *}
lemma add_less_mono1: "i < j ==> i + k < j + (k::nat)"
by (induct k) simp_all

text {* strict, in both arguments *}
lemma add_less_mono: "[|i < j; k < l|] ==> i + k < j + (l::nat)"
  apply (rule add_less_mono1 [THEN less_trans], assumption+)
  apply (induct j, simp_all)
  done

text {* Deleted @{text less_natE}; use @{text "less_imp_Suc_add RS exE"} *}
lemma less_imp_Suc_add: "m < n ==> (∃k. n = Suc (m + k))"
  apply (induct n)
  apply (simp_all add: order_le_less)
  apply (blast elim!: less_SucE
               intro!: add_0_right [symmetric] add_Suc_right [symmetric])
  done

text {* strict, in 1st argument; proof is by induction on @{text "k > 0"} *}
lemma mult_less_mono2: "(i::nat) < j ==> 0<k ==> k * i < k * j"
apply(auto simp: gr0_conv_Suc)
apply (induct_tac m)
apply (simp_all add: add_less_mono)
done

text{*The naturals form an ordered @{text comm_semiring_1_cancel}*}
instance nat :: ordered_semidom
proof
  fix i j k :: nat
  show "0 < (1::nat)" by simp
  show "i ≤ j ==> k + i ≤ k + j" by simp
  show "i < j ==> 0 < k ==> k * i < k * j" by (simp add: mult_less_mono2)
qed

lemma nat_mult_1: "(1::nat) * n = n"
by simp

lemma nat_mult_1_right: "n * (1::nat) = n"
by simp


subsubsection {* Additional theorems about @{term "op ≤"} *}

text {* Complete induction, aka course-of-values induction *}

lemma less_induct [case_names less]:
  fixes P :: "nat => bool"
  assumes step: "!!x. (!!y. y < x ==> P y) ==> P x"
  shows "P a"
proof - 
  have "!!z. z≤a ==> P z"
  proof (induct a)
    case (0 z)
    have "P 0" by (rule step) auto
    thus ?case using 0 by auto
  next
    case (Suc x z)
    then have "z ≤ x ∨ z = Suc x" by (simp add: le_Suc_eq)
    thus ?case
    proof
      assume "z ≤ x" thus "P z" by (rule Suc(1))
    next
      assume z: "z = Suc x"
      show "P z"
        by (rule step) (rule Suc(1), simp add: z le_simps)
    qed
  qed
  thus ?thesis by auto
qed

lemma nat_less_induct:
  assumes "!!n. ∀m::nat. m < n --> P m ==> P n" shows "P n"
  using assms less_induct by blast

lemma measure_induct_rule [case_names less]:
  fixes f :: "'a => nat"
  assumes step: "!!x. (!!y. f y < f x ==> P y) ==> P x"
  shows "P a"
by (induct m≡"f a" arbitrary: a rule: less_induct) (auto intro: step)

text {* old style induction rules: *}
lemma measure_induct:
  fixes f :: "'a => nat"
  shows "(!!x. ∀y. f y < f x --> P y ==> P x) ==> P a"
  by (rule measure_induct_rule [of f P a]) iprover

lemma full_nat_induct:
  assumes step: "(!!n. (ALL m. Suc m <= n --> P m) ==> P n)"
  shows "P n"
  by (rule less_induct) (auto intro: step simp:le_simps)

text{*An induction rule for estabilishing binary relations*}
lemma less_Suc_induct:
  assumes less:  "i < j"
     and  step:  "!!i. P i (Suc i)"
     and  trans: "!!i j k. P i j ==> P j k ==> P i k"
  shows "P i j"
proof -
  from less obtain k where j: "j = Suc(i+k)" by (auto dest: less_imp_Suc_add)
  have "P i (Suc (i + k))"
  proof (induct k)
    case 0
    show ?case by (simp add: step)
  next
    case (Suc k)
    thus ?case by (auto intro: assms)
  qed
  thus "P i j" by (simp add: j)
qed

lemma nat_induct2: "[|P 0; P (Suc 0); !!k. P k ==> P (Suc (Suc k))|] ==> P n"
  apply (rule nat_less_induct)
  apply (case_tac n)
  apply (case_tac [2] nat)
  apply (blast intro: less_trans)+
  done

text {* The method of infinite descent, frequently used in number theory.
Provided by Roelof Oosterhuis.
$P(n)$ is true for all $n\in\mathbb{N}$ if
\begin{itemize}
  \item case ``0'': given $n=0$ prove $P(n)$,
  \item case ``smaller'': given $n>0$ and $\neg P(n)$ prove there exists
        a smaller integer $m$ such that $\neg P(m)$.
\end{itemize} *}

text{* A compact version without explicit base case: *}
lemma infinite_descent:
  "[| !!n::nat. ¬ P n ==>  ∃m<n. ¬  P m |] ==>  P n"
by (induct n rule: less_induct, auto)

lemma infinite_descent0[case_names 0 smaller]: 
  "[| P 0; !!n. n>0 ==> ¬ P n ==> (∃m::nat. m < n ∧ ¬P m) |] ==> P n"
by (rule infinite_descent) (case_tac "n>0", auto)

text {*
Infinite descent using a mapping to $\mathbb{N}$:
$P(x)$ is true for all $x\in D$ if there exists a $V: D \to \mathbb{N}$ and
\begin{itemize}
\item case ``0'': given $V(x)=0$ prove $P(x)$,
\item case ``smaller'': given $V(x)>0$ and $\neg P(x)$ prove there exists a $y \in D$ such that $V(y)<V(x)$ and $~\neg P(y)$.
\end{itemize}
NB: the proof also shows how to use the previous lemma. *}

corollary infinite_descent0_measure [case_names 0 smaller]:
  assumes A0: "!!x. V x = (0::nat) ==> P x"
    and   A1: "!!x. V x > 0 ==> ¬P x ==> (∃y. V y < V x ∧ ¬P y)"
  shows "P x"
proof -
  obtain n where "n = V x" by auto
  moreover have "!!x. V x = n ==> P x"
  proof (induct n rule: infinite_descent0)
    case 0 -- "i.e. $V(x) = 0$"
    with A0 show "P x" by auto
  next -- "now $n>0$ and $P(x)$ does not hold for some $x$ with $V(x)=n$"
    case (smaller n)
    then obtain x where vxn: "V x = n " and "V x > 0 ∧ ¬ P x" by auto
    with A1 obtain y where "V y < V x ∧ ¬ P y" by auto
    with vxn obtain m where "m = V y ∧ m<n ∧ ¬ P y" by auto
    then show ?case by auto
  qed
  ultimately show "P x" by auto
qed

text{* Again, without explicit base case: *}
lemma infinite_descent_measure:
assumes "!!x. ¬ P x ==> ∃y. (V::'a=>nat) y < V x ∧ ¬ P y" shows "P x"
proof -
  from assms obtain n where "n = V x" by auto
  moreover have "!!x. V x = n ==> P x"
  proof (induct n rule: infinite_descent, auto)
    fix x assume "¬ P x"
    with assms show "∃m < V x. ∃y. V y = m ∧ ¬ P y" by auto
  qed
  ultimately show "P x" by auto
qed

text {* A [clumsy] way of lifting @{text "<"}
  monotonicity to @{text "≤"} monotonicity *}
lemma less_mono_imp_le_mono:
  "[| !!i j::nat. i < j ==> f i < f j; i ≤ j |] ==> f i ≤ ((f j)::nat)"
by (simp add: order_le_less) (blast)


text {* non-strict, in 1st argument *}
lemma add_le_mono1: "i ≤ j ==> i + k ≤ j + (k::nat)"
by (rule add_right_mono)

text {* non-strict, in both arguments *}
lemma add_le_mono: "[| i ≤ j;  k ≤ l |] ==> i + k ≤ j + (l::nat)"
by (rule add_mono)

lemma le_add2: "n ≤ ((m + n)::nat)"
by (insert add_right_mono [of 0 m n], simp)

lemma le_add1: "n ≤ ((n + m)::nat)"
by (simp add: add_commute, rule le_add2)

lemma less_add_Suc1: "i < Suc (i + m)"
by (rule le_less_trans, rule le_add1, rule lessI)

lemma less_add_Suc2: "i < Suc (m + i)"
by (rule le_less_trans, rule le_add2, rule lessI)

lemma less_iff_Suc_add: "(m < n) = (∃k. n = Suc (m + k))"
by (iprover intro!: less_add_Suc1 less_imp_Suc_add)

lemma trans_le_add1: "(i::nat) ≤ j ==> i ≤ j + m"
by (rule le_trans, assumption, rule le_add1)

lemma trans_le_add2: "(i::nat) ≤ j ==> i ≤ m + j"
by (rule le_trans, assumption, rule le_add2)

lemma trans_less_add1: "(i::nat) < j ==> i < j + m"
by (rule less_le_trans, assumption, rule le_add1)

lemma trans_less_add2: "(i::nat) < j ==> i < m + j"
by (rule less_le_trans, assumption, rule le_add2)

lemma add_lessD1: "i + j < (k::nat) ==> i < k"
apply (rule le_less_trans [of _ "i+j"])
apply (simp_all add: le_add1)
done

lemma not_add_less1 [iff]: "~ (i + j < (i::nat))"
apply (rule notI)
apply (drule add_lessD1)
apply (erule less_irrefl [THEN notE])
done

lemma not_add_less2 [iff]: "~ (j + i < (i::nat))"
by (simp add: add_commute)

lemma add_leD1: "m + k ≤ n ==> m ≤ (n::nat)"
apply (rule order_trans [of _ "m+k"])
apply (simp_all add: le_add1)
done

lemma add_leD2: "m + k ≤ n ==> k ≤ (n::nat)"
apply (simp add: add_commute)
apply (erule add_leD1)
done

lemma add_leE: "(m::nat) + k ≤ n ==> (m ≤ n ==> k ≤ n ==> R) ==> R"
by (blast dest: add_leD1 add_leD2)

text {* needs @{text "!!k"} for @{text add_ac} to work *}
lemma less_add_eq_less: "!!k::nat. k < l ==> m + l = k + n ==> m < n"
by (force simp del: add_Suc_right
    simp add: less_iff_Suc_add add_Suc_right [symmetric] add_ac)


subsubsection {* More results about difference *}

text {* Addition is the inverse of subtraction:
  if @{term "n ≤ m"} then @{term "n + (m - n) = m"}. *}
lemma add_diff_inverse: "~  m < n ==> n + (m - n) = (m::nat)"
by (induct m n rule: diff_induct) simp_all

lemma le_add_diff_inverse [simp]: "n ≤ m ==> n + (m - n) = (m::nat)"
by (simp add: add_diff_inverse linorder_not_less)

lemma le_add_diff_inverse2 [simp]: "n ≤ m ==> (m - n) + n = (m::nat)"
by (simp add: add_commute)

lemma Suc_diff_le: "n ≤ m ==> Suc m - n = Suc (m - n)"
by (induct m n rule: diff_induct) simp_all

lemma diff_less_Suc: "m - n < Suc m"
apply (induct m n rule: diff_induct)
apply (erule_tac [3] less_SucE)
apply (simp_all add: less_Suc_eq)
done

lemma diff_le_self [simp]: "m - n ≤ (m::nat)"
by (induct m n rule: diff_induct) (simp_all add: le_SucI)

lemma le_iff_add: "(m::nat) ≤ n = (∃k. n = m + k)"
  by (auto simp: le_add1 dest!: le_add_diff_inverse sym [of _ n])

lemma less_imp_diff_less: "(j::nat) < k ==> j - n < k"
by (rule le_less_trans, rule diff_le_self)

lemma diff_Suc_less [simp]: "0<n ==> n - Suc i < n"
by (cases n) (auto simp add: le_simps)

lemma diff_add_assoc: "k ≤ (j::nat) ==> (i + j) - k = i + (j - k)"
by (induct j k rule: diff_induct) simp_all

lemma diff_add_assoc2: "k ≤ (j::nat) ==> (j + i) - k = (j - k) + i"
by (simp add: add_commute diff_add_assoc)

lemma le_imp_diff_is_add: "i ≤ (j::nat) ==> (j - i = k) = (j = k + i)"
by (auto simp add: diff_add_inverse2)

lemma diff_is_0_eq [simp]: "((m::nat) - n = 0) = (m ≤ n)"
by (induct m n rule: diff_induct) simp_all

lemma diff_is_0_eq' [simp]: "m ≤ n ==> (m::nat) - n = 0"
by (rule iffD2, rule diff_is_0_eq)

lemma zero_less_diff [simp]: "(0 < n - (m::nat)) = (m < n)"
by (induct m n rule: diff_induct) simp_all

lemma less_imp_add_positive:
  assumes "i < j"
  shows "∃k::nat. 0 < k & i + k = j"
proof
  from assms show "0 < j - i & i + (j - i) = j"
    by (simp add: order_less_imp_le)
qed

text {* a nice rewrite for bounded subtraction *}
lemma nat_minus_add_max:
  fixes n m :: nat
  shows "n - m + m = max n m"
    by (simp add: max_def not_le order_less_imp_le)

lemma nat_diff_split:
  "P(a - b::nat) = ((a<b --> P 0) & (ALL d. a = b + d --> P d))"
    -- {* elimination of @{text -} on @{text nat} *}
by (cases "a < b")
  (auto simp add: diff_is_0_eq [THEN iffD2] diff_add_inverse
    not_less le_less dest!: sym [of a] sym [of b] add_eq_self_zero)

lemma nat_diff_split_asm:
  "P(a - b::nat) = (~ (a < b & ~ P 0 | (EX d. a = b + d & ~ P d)))"
    -- {* elimination of @{text -} on @{text nat} in assumptions *}
by (auto split: nat_diff_split)


subsubsection {* Monotonicity of Multiplication *}

lemma mult_le_mono1: "i ≤ (j::nat) ==> i * k ≤ j * k"
by (simp add: mult_right_mono)

lemma mult_le_mono2: "i ≤ (j::nat) ==> k * i ≤ k * j"
by (simp add: mult_left_mono)

text {* @{text "≤"} monotonicity, BOTH arguments *}
lemma mult_le_mono: "i ≤ (j::nat) ==> k ≤ l ==> i * k ≤ j * l"
by (simp add: mult_mono)

lemma mult_less_mono1: "(i::nat) < j ==> 0 < k ==> i * k < j * k"
by (simp add: mult_strict_right_mono)

text{*Differs from the standard @{text zero_less_mult_iff} in that
      there are no negative numbers.*}
lemma nat_0_less_mult_iff [simp]: "(0 < (m::nat) * n) = (0 < m & 0 < n)"
  apply (induct m)
   apply simp
  apply (case_tac n)
   apply simp_all
  done

lemma one_le_mult_iff [simp]: "(Suc 0 ≤ m * n) = (1 ≤ m & 1 ≤ n)"
  apply (induct m)
   apply simp
  apply (case_tac n)
   apply simp_all
  done

lemma mult_less_cancel2 [simp]: "((m::nat) * k < n * k) = (0 < k & m < n)"
  apply (safe intro!: mult_less_mono1)
  apply (case_tac k, auto)
  apply (simp del: le_0_eq add: linorder_not_le [symmetric])
  apply (blast intro: mult_le_mono1)
  done

lemma mult_less_cancel1 [simp]: "(k * (m::nat) < k * n) = (0 < k & m < n)"
by (simp add: mult_commute [of k])

lemma mult_le_cancel1 [simp]: "(k * (m::nat) ≤ k * n) = (0 < k --> m ≤ n)"
by (simp add: linorder_not_less [symmetric], auto)

lemma mult_le_cancel2 [simp]: "((m::nat) * k ≤ n * k) = (0 < k --> m ≤ n)"
by (simp add: linorder_not_less [symmetric], auto)

lemma Suc_mult_less_cancel1: "(Suc k * m < Suc k * n) = (m < n)"
by (subst mult_less_cancel1) simp

lemma Suc_mult_le_cancel1: "(Suc k * m ≤ Suc k * n) = (m ≤ n)"
by (subst mult_le_cancel1) simp

lemma le_square: "m ≤ m * (m::nat)"
  by (cases m) (auto intro: le_add1)

lemma le_cube: "(m::nat) ≤ m * (m * m)"
  by (cases m) (auto intro: le_add1)

text {* Lemma for @{text gcd} *}
lemma mult_eq_self_implies_10: "(m::nat) = m * n ==> n = 1 | m = 0"
  apply (drule sym)
  apply (rule disjCI)
  apply (rule nat_less_cases, erule_tac [2] _)
   apply (drule_tac [2] mult_less_mono2)
    apply (auto)
  done

text {* the lattice order on @{typ nat} *}

instantiation nat :: distrib_lattice
begin

definition
  "(inf :: nat => nat => nat) = min"

definition
  "(sup :: nat => nat => nat) = max"

instance by intro_classes
  (auto simp add: inf_nat_def sup_nat_def max_def not_le min_def
    intro: order_less_imp_le antisym elim!: order_trans order_less_trans)

end


subsection {* Embedding of the Naturals into any
  @{text semiring_1}: @{term of_nat} *}

context semiring_1
begin

primrec
  of_nat :: "nat => 'a"
where
  of_nat_0:     "of_nat 0 = 0"
  | of_nat_Suc: "of_nat (Suc m) = 1 + of_nat m"

lemma of_nat_1 [simp]: "of_nat 1 = 1"
  by simp

lemma of_nat_add [simp]: "of_nat (m + n) = of_nat m + of_nat n"
  by (induct m) (simp_all add: add_ac)

lemma of_nat_mult: "of_nat (m * n) = of_nat m * of_nat n"
  by (induct m) (simp_all add: add_ac left_distrib)

definition
  of_nat_aux :: "nat => 'a => 'a"
where
  [code func del]: "of_nat_aux n i = of_nat n + i"

lemma of_nat_aux_code [code]:
  "of_nat_aux 0 i = i"
  "of_nat_aux (Suc n) i = of_nat_aux n (i + 1)" -- {* tail recursive *}
  by (simp_all add: of_nat_aux_def add_ac)

lemma of_nat_code [code]:
  "of_nat n = of_nat_aux n 0"
  by (simp add: of_nat_aux_def)

end

text{*Class for unital semirings with characteristic zero.
 Includes non-ordered rings like the complex numbers.*}

class semiring_char_0 = semiring_1 +
  assumes of_nat_eq_iff [simp]: "of_nat m = of_nat n <-> m = n"
begin

text{*Special cases where either operand is zero*}

lemma of_nat_0_eq_iff [simp, noatp]: "0 = of_nat n <-> 0 = n"
  by (rule of_nat_eq_iff [of 0, simplified])

lemma of_nat_eq_0_iff [simp, noatp]: "of_nat m = 0 <-> m = 0"
  by (rule of_nat_eq_iff [of _ 0, simplified])

lemma inj_of_nat: "inj of_nat"
  by (simp add: inj_on_def)

end

context ordered_semidom
begin

lemma zero_le_imp_of_nat: "0 ≤ of_nat m"
  apply (induct m, simp_all)
  apply (erule order_trans)
  apply (rule ord_le_eq_trans [OF _ add_commute])
  apply (rule less_add_one [THEN less_imp_le])
  done

lemma less_imp_of_nat_less: "m < n ==> of_nat m < of_nat n"
  apply (induct m n rule: diff_induct, simp_all)
  apply (insert add_less_le_mono [OF zero_less_one zero_le_imp_of_nat], force)
  done

lemma of_nat_less_imp_less: "of_nat m < of_nat n ==> m < n"
  apply (induct m n rule: diff_induct, simp_all)
  apply (insert zero_le_imp_of_nat)
  apply (force simp add: not_less [symmetric])
  done

lemma of_nat_less_iff [simp]: "of_nat m < of_nat n <-> m < n"
  by (blast intro: of_nat_less_imp_less less_imp_of_nat_less)

lemma of_nat_le_iff [simp]: "of_nat m ≤ of_nat n <-> m ≤ n"
  by (simp add: not_less [symmetric] linorder_not_less [symmetric])

text{*Every @{text ordered_semidom} has characteristic zero.*}

subclass semiring_char_0
  by unfold_locales (simp add: eq_iff order_eq_iff)

text{*Special cases where either operand is zero*}

lemma of_nat_0_le_iff [simp]: "0 ≤ of_nat n"
  by (rule of_nat_le_iff [of 0, simplified])

lemma of_nat_le_0_iff [simp, noatp]: "of_nat m ≤ 0 <-> m = 0"
  by (rule of_nat_le_iff [of _ 0, simplified])

lemma of_nat_0_less_iff [simp]: "0 < of_nat n <-> 0 < n"
  by (rule of_nat_less_iff [of 0, simplified])

lemma of_nat_less_0_iff [simp]: "¬ of_nat m < 0"
  by (rule of_nat_less_iff [of _ 0, simplified])

end

context ring_1
begin

lemma of_nat_diff: "n ≤ m ==> of_nat (m - n) = of_nat m - of_nat n"
  by (simp add: compare_rls of_nat_add [symmetric])

end

context ordered_idom
begin

lemma abs_of_nat [simp]: "¦of_nat n¦ = of_nat n"
  unfolding abs_if by auto

end

lemma of_nat_id [simp]: "of_nat n = n"
  by (induct n) auto

lemma of_nat_eq_id [simp]: "of_nat = id"
  by (auto simp add: expand_fun_eq)


subsection {* The Set of Natural Numbers *}

context semiring_1
begin

definition
  Nats  :: "'a set" where
  "Nats = range of_nat"

notation (xsymbols)
  Nats  ("\<nat>")

lemma of_nat_in_Nats [simp]: "of_nat n ∈ \<nat>"
  by (simp add: Nats_def)

lemma Nats_0 [simp]: "0 ∈ \<nat>"
apply (simp add: Nats_def)
apply (rule range_eqI)
apply (rule of_nat_0 [symmetric])
done

lemma Nats_1 [simp]: "1 ∈ \<nat>"
apply (simp add: Nats_def)
apply (rule range_eqI)
apply (rule of_nat_1 [symmetric])
done

lemma Nats_add [simp]: "a ∈ \<nat> ==> b ∈ \<nat> ==> a + b ∈ \<nat>"
apply (auto simp add: Nats_def)
apply (rule range_eqI)
apply (rule of_nat_add [symmetric])
done

lemma Nats_mult [simp]: "a ∈ \<nat> ==> b ∈ \<nat> ==> a * b ∈ \<nat>"
apply (auto simp add: Nats_def)
apply (rule range_eqI)
apply (rule of_nat_mult [symmetric])
done

end


subsection {* Further Arithmetic Facts Concerning the Natural Numbers *}

lemma subst_equals:
  assumes 1: "t = s" and 2: "u = t"
  shows "u = s"
  using 2 1 by (rule trans)

use "arith_data.ML"
declaration {* K ArithData.setup *}

use "Tools/lin_arith.ML"
declaration {* K LinArith.setup *}

lemmas [arith_split] = nat_diff_split split_min split_max

text{*Subtraction laws, mostly by Clemens Ballarin*}

lemma diff_less_mono: "[| a < (b::nat); c ≤ a |] ==> a-c < b-c"
by arith

lemma less_diff_conv: "(i < j-k) = (i+k < (j::nat))"
by arith

lemma le_diff_conv: "(j-k ≤ (i::nat)) = (j ≤ i+k)"
by arith

lemma le_diff_conv2: "k ≤ j ==> (i ≤ j-k) = (i+k ≤ (j::nat))"
by arith

lemma diff_diff_cancel [simp]: "i ≤ (n::nat) ==> n - (n - i) = i"
by arith

lemma le_add_diff: "k ≤ (n::nat) ==> m ≤ n + m - k"
by arith

(*Replaces the previous diff_less and le_diff_less, which had the stronger
  second premise n≤m*)
lemma diff_less[simp]: "!!m::nat. [| 0<n; 0<m |] ==> m - n < m"
by arith

text {* Simplification of relational expressions involving subtraction *}

lemma diff_diff_eq: "[| k ≤ m;  k ≤ (n::nat) |] ==> ((m-k) - (n-k)) = (m-n)"
by (simp split add: nat_diff_split)

lemma eq_diff_iff: "[| k ≤ m;  k ≤ (n::nat) |] ==> (m-k = n-k) = (m=n)"
by (auto split add: nat_diff_split)

lemma less_diff_iff: "[| k ≤ m;  k ≤ (n::nat) |] ==> (m-k < n-k) = (m<n)"
by (auto split add: nat_diff_split)

lemma le_diff_iff: "[| k ≤ m;  k ≤ (n::nat) |] ==> (m-k ≤ n-k) = (m≤n)"
by (auto split add: nat_diff_split)

text{*(Anti)Monotonicity of subtraction -- by Stephan Merz*}

(* Monotonicity of subtraction in first argument *)
lemma diff_le_mono: "m ≤ (n::nat) ==> (m-l) ≤ (n-l)"
by (simp split add: nat_diff_split)

lemma diff_le_mono2: "m ≤ (n::nat) ==> (l-n) ≤ (l-m)"
by (simp split add: nat_diff_split)

lemma diff_less_mono2: "[| m < (n::nat); m<l |] ==> (l-n) < (l-m)"
by (simp split add: nat_diff_split)

lemma diffs0_imp_equal: "!!m::nat. [| m-n = 0; n-m = 0 |] ==>  m=n"
by (simp split add: nat_diff_split)

lemma min_diff: "min (m - (i::nat)) (n - i) = min m n - i"
unfolding min_def by auto

lemma inj_on_diff_nat: 
  assumes k_le_n: "∀n ∈ N. k ≤ (n::nat)"
  shows "inj_on (λn. n - k) N"
proof (rule inj_onI)
  fix x y
  assume a: "x ∈ N" "y ∈ N" "x - k = y - k"
  with k_le_n have "x - k + k = y - k + k" by auto
  with a k_le_n show "x = y" by auto
qed

text{*Rewriting to pull differences out*}

lemma diff_diff_right [simp]: "k≤j --> i - (j - k) = i + (k::nat) - j"
by arith

lemma diff_Suc_diff_eq1 [simp]: "k ≤ j ==> m - Suc (j - k) = m + k - Suc j"
by arith

lemma diff_Suc_diff_eq2 [simp]: "k ≤ j ==> Suc (j - k) - m = Suc j - (k + m)"
by arith

text{*Lemmas for ex/Factorization*}

lemma one_less_mult: "[| Suc 0 < n; Suc 0 < m |] ==> Suc 0 < m*n"
by (cases m) auto

lemma n_less_m_mult_n: "[| Suc 0 < n; Suc 0 < m |] ==> n<m*n"
by (cases m) auto

lemma n_less_n_mult_m: "[| Suc 0 < n; Suc 0 < m |] ==> n<n*m"
by (cases m) auto

text {* Specialized induction principles that work "backwards": *}

lemma inc_induct[consumes 1, case_names base step]:
  assumes less: "i <= j"
  assumes base: "P j"
  assumes step: "!!i. [| i < j; P (Suc i) |] ==> P i"
  shows "P i"
  using less
proof (induct d=="j - i" arbitrary: i)
  case (0 i)
  hence "i = j" by simp
  with base show ?case by simp
next
  case (Suc d i)
  hence "i < j" "P (Suc i)"
    by simp_all
  thus "P i" by (rule step)
qed

lemma strict_inc_induct[consumes 1, case_names base step]:
  assumes less: "i < j"
  assumes base: "!!i. j = Suc i ==> P i"
  assumes step: "!!i. [| i < j; P (Suc i) |] ==> P i"
  shows "P i"
  using less
proof (induct d=="j - i - 1" arbitrary: i)
  case (0 i)
  with `i < j` have "j = Suc i" by simp
  with base show ?case by simp
next
  case (Suc d i)
  hence "i < j" "P (Suc i)"
    by simp_all
  thus "P i" by (rule step)
qed

lemma zero_induct_lemma: "P k ==> (!!n. P (Suc n) ==> P n) ==> P (k - i)"
  using inc_induct[of "k - i" k P, simplified] by blast

lemma zero_induct: "P k ==> (!!n. P (Suc n) ==> P n) ==> P 0"
  using inc_induct[of 0 k P] by blast

lemma nat_not_singleton: "(∀x. x = (0::nat)) = False"
  by auto

(*The others are
      i - j - k = i - (j + k),
      k ≤ j ==> j - k + i = j + i - k,
      k ≤ j ==> i + (j - k) = i + j - k *)
lemmas add_diff_assoc = diff_add_assoc [symmetric]
lemmas add_diff_assoc2 = diff_add_assoc2[symmetric]
declare diff_diff_left [simp]  add_diff_assoc [simp] add_diff_assoc2[simp]

text{*At present we prove no analogue of @{text not_less_Least} or @{text
Least_Suc}, since there appears to be no need.*}

subsection {* size of a datatype value *}

class size = type +
  fixes size :: "'a => nat" -- {* see further theory @{text Wellfounded} *}

end

Type @{text ind}

Type nat

lemma nat_induct:

  [| P 0; !!n. P n ==> P (Suc n) |] ==> P n

lemma Suc_not_Zero:

  Suc m  0

lemma Zero_not_Suc:

  0  Suc m

lemma inj_Suc:

  inj_on Suc N

lemma Suc_Suc_eq:

  (Suc m = Suc n) = (m = n)

lemma nat_rec_0:

  nat_rec f1.0 f2.0 0 = f1.0

and nat_rec_Suc:

  nat_rec f1.0 f2.0 (Suc nat) = f2.0 nat (nat_rec f1.0 f2.0 nat)

lemma nat_case_0:

  nat_case f1.0 f2.0 0 = f1.0

and nat_case_Suc:

  nat_case f1.0 f2.0 (Suc nat) = f2.0 nat

lemma Suc_neq_Zero:

  Suc m = 0 ==> R

lemma Zero_neq_Suc:

  0 = Suc m ==> R

lemma Suc_inject:

  Suc x = Suc y ==> x = y

lemma n_not_Suc_n:

  n  Suc n

lemma Suc_n_not_n:

  Suc n  n

lemma diff_induct:

  [| !!x. P x 0; !!y. P 0 (Suc y); !!x y. P x y ==> P (Suc x) (Suc y) |] ==> P m n

Arithmetic operators

lemma add_0_right:

  m + 0 = m

lemma add_Suc_right:

  m + Suc n = Suc (m + n)

lemma add_Suc_shift:

  Suc m + n = m + Suc n

lemma diff_0_eq_0:

  0 - n = 0

lemma diff_Suc_Suc:

  Suc m - Suc n = m - n

lemma mult_0_right:

  m * 0 = 0

lemma mult_Suc_right:

  m * Suc n = m + m * n

lemma add_mult_distrib:

  (m + n) * k = m * k + n * k

Addition

lemma nat_add_assoc:

  m + n + k = m + (n + k)

lemma nat_add_commute:

  m + n = n + m

lemma nat_add_left_commute:

  x + (y + z) = y + (x + z)

lemma nat_add_left_cancel:

  (k + m = k + n) = (m = n)

lemma nat_add_right_cancel:

  (m + k = n + k) = (m = n)

lemma add_is_0:

  (m + n = 0) = (m = 0n = 0)

lemma add_is_1:

  (m + n = Suc 0) = (m = Suc 0n = 0m = 0n = Suc 0)

lemma one_is_add:

  (Suc 0 = m + n) = (m = Suc 0n = 0m = 0n = Suc 0)

lemma add_eq_self_zero:

  m + n = m ==> n = 0

lemma inj_on_add_nat:

  inj_on (λn. n + k) N

Difference

lemma diff_self_eq_0:

  m - m = 0

lemma diff_diff_left:

  i - j - k = i - (j + k)

lemma Suc_diff_diff:

  Suc m - n - Suc k = m - n - k

lemma diff_commute:

  i - j - k = i - k - j

lemma diff_add_inverse:

  n + m - n = m

lemma diff_add_inverse2:

  m + n - n = m

lemma diff_cancel:

  k + m - (k + n) = m - n

lemma diff_cancel2:

  m + k - (n + k) = m - n

lemma diff_add_0:

  n - (n + m) = 0

lemma diff_mult_distrib:

  (m - n) * k = m * k - n * k

lemma diff_mult_distrib2:

  k * (m - n) = k * m - k * n

Multiplication

lemma nat_mult_assoc:

  m * n * k = m * (n * k)

lemma nat_mult_commute:

  m * n = n * m

lemma add_mult_distrib2:

  k * (m + n) = k * m + k * n

lemma mult_is_0:

  (m * n = 0) = (m = 0n = 0)

lemma nat_distrib:

  (m + n) * k = m * k + n * k
  k * (m + n) = k * m + k * n
  (m - n) * k = m * k - n * k
  k * (m - n) = k * m - k * n

lemma mult_eq_1_iff:

  (m * n = Suc 0) = (m = 1n = 1)

lemma one_eq_mult_iff:

  (Suc 0 = m * n) = (m = 1n = 1)

lemma mult_cancel1:

  (k * m = k * n) = (m = nk = 0)

lemma mult_cancel2:

  (m * k = n * k) = (m = nk = 0)

lemma Suc_mult_cancel1:

  (Suc k * m = Suc k * n) = (m = n)

Orders on @{typ nat}

Operation definition

lemma

  (0  n) = True

lemma le0:

  0  n

lemma Suc_le_mono:

  (Suc n  Suc m) = (n  m)

lemma Suc_le_eq:

  (Suc m  n) = (m < n)

lemma le_0_eq:

  (n  0) = (n = 0)

lemma not_less0:

  ¬ n < 0

lemma less_nat_zero_code:

  (n < 0) = False

lemma Suc_less_eq:

  (Suc m < Suc n) = (m < n)

lemma less_Suc_eq_le:

  (m < Suc n) = (m  n)

lemma le_SucI:

  m  n ==> m  Suc n

lemma Suc_leD:

  Suc m  n ==> m  n

lemma less_SucI:

  m < n ==> m < Suc n

lemma Suc_lessD:

  Suc m < n ==> m < n

Introduction properties

lemma lessI:

  n < Suc n

lemma zero_less_Suc:

  0 < Suc n

Elimination properties

lemma less_not_refl:

  ¬ n < n

lemma less_not_refl2:

  n < m ==> m  n

lemma less_not_refl3:

  s < t ==> s  t

lemma less_irrefl_nat:

  n < n ==> R

lemma less_zeroE:

  n < 0 ==> R

lemma less_Suc_eq:

  (m < Suc n) = (m < nm = n)

lemma less_one:

  (n < 1) = (n = 0)

lemma less_Suc0:

  (n < Suc 0) = (n = 0)

lemma Suc_mono:

  m < n ==> Suc m < Suc n

lemma less_antisym:

  [| ¬ n < m; n < Suc m |] ==> m = n

lemma nat_neq_iff:

  (m  n) = (m < nn < m)

lemma nat_less_cases:

  [| m < n ==> P n m; m = n ==> P n m; n < m ==> P n m |] ==> P n m

Inductive (?) properties

lemma Suc_lessI:

  [| m < n; Suc m  n |] ==> Suc m < n

lemma lessE:

  [| i < k; k = Suc i ==> P; !!j. [| i < j; k = Suc j |] ==> P |] ==> P

lemma less_SucE:

  [| m < Suc n; m < n ==> P; m = n ==> P |] ==> P

lemma Suc_lessE:

  [| Suc i < k; !!j. [| i < j; k = Suc j |] ==> P |] ==> P

lemma Suc_less_SucD:

  Suc m < Suc n ==> m < n

lemma less_trans_Suc:

  [| i < j; j < k |] ==> Suc i < k

lemma not_less_eq:

  m < n) = (n < Suc m)

lemma not_less_eq_eq:

  m  n) = (Suc n  m)

lemma le_imp_less_Suc:

  m  n ==> m < Suc n

lemma Suc_n_not_le_n:

  ¬ Suc n  n

lemma le_Suc_eq:

  (m  Suc n) = (m  nm = Suc n)

lemma le_SucE:

  [| m  Suc n; m  n ==> R; m = Suc n ==> R |] ==> R

lemma Suc_leI:

  m < n ==> Suc m  n

lemma Suc_le_lessD:

  Suc m  n ==> m < n

lemma less_imp_le_nat:

  m < n ==> m  n

lemma le_simps:

  m < n ==> m  n
  (m < Suc n) = (m  n)
  (Suc m  n) = (m < n)

lemma less_or_eq_imp_le:

  m < nm = n ==> m  n

lemma le_eq_less_or_eq:

  (m  n) = (m < nm = n)

lemma eq_imp_le:

  m = n ==> m  n

lemma le_refl:

  n  n

lemma le_trans:

  [| i  j; j  k |] ==> i  k

lemma le_anti_sym:

  [| m  n; n  m |] ==> m = n

lemma nat_less_le:

  (m < n) = (m  nm  n)

lemma le_neq_implies_less:

  [| m  n; m  n |] ==> m < n

lemma nat_le_linear:

  m  nn  m

lemma linorder_neqE_nat:

  [| x  y; x < y ==> R; y < x ==> R |] ==> R

lemma le_less_Suc_eq:

  m  n ==> (n < Suc m) = (n = m)

lemma not_less_less_Suc_eq:

  ¬ n < m ==> (n < Suc m) = (n = m)

lemma not_less_simps:

  ¬ n < m ==> (n < Suc m) = (n = m)
  m  n ==> (n < Suc m) = (n = m)

lemma def_nat_rec_0:

  (!!n. f n == nat_rec c h n) ==> f 0 = c

lemma def_nat_rec_Suc:

  (!!n. f n == nat_rec c h n) ==> f (Suc n) = h n (f n)

lemma not0_implies_Suc:

  n  0 ==> ∃m. n = Suc m

lemma gr0_implies_Suc:

  0 < n ==> ∃m. n = Suc m

lemma gr_implies_not0:

  m < n ==> n  0

lemma neq0_conv:

  (n  0) = (0 < n)

lemma gr0I:

  (n = 0 ==> False) ==> 0 < n

lemma gr0_conv_Suc:

  (0 < n) = (∃m. n = Suc m)

lemma not_gr0:

  0 < n) = (n = 0)

lemma Suc_le_D:

  Suc n  m' ==> ∃m. m' = Suc m

lemma less_Suc_eq_0_disj:

  (m < Suc n) = (m = 0 ∨ (∃j. m = Suc jj < n))

@{term min} and @{term max}

lemma mono_Suc:

  mono Suc

lemma min_0L:

  min 0 n = 0

lemma min_0R:

  min n 0 = 0

lemma min_Suc_Suc:

  min (Suc m) (Suc n) = Suc (min m n)

lemma min_Suc1:

  min (Suc n) m = (case m of 0 => 0 | Suc m' => Suc (min n m'))

lemma min_Suc2:

  min m (Suc n) = (case m of 0 => 0 | Suc m' => Suc (min m' n))

lemma max_0L:

  max 0 n = n

lemma max_0R:

  max n 0 = n

lemma max_Suc_Suc:

  max (Suc m) (Suc n) = Suc (max m n)

lemma max_Suc1:

  max (Suc n) m = (case m of 0 => Suc n | Suc m' => Suc (max n m'))

lemma max_Suc2:

  max m (Suc n) = (case m of 0 => Suc n | Suc m' => Suc (max m' n))

Monotonicity of Addition

lemma Suc_pred:

  0 < n ==> Suc (n - Suc 0) = n

lemma nat_add_left_cancel_le:

  (k + m  k + n) = (m  n)

lemma nat_add_left_cancel_less:

  (k + m < k + n) = (m < n)

lemma add_gr_0:

  (0 < m + n) = (0 < m0 < n)

lemma add_less_mono1:

  i < j ==> i + k < j + k

lemma add_less_mono:

  [| i < j; k < l |] ==> i + k < j + l

lemma less_imp_Suc_add:

  m < n ==> ∃k. n = Suc (m + k)

lemma mult_less_mono2:

  [| i < j; 0 < k |] ==> k * i < k * j

lemma nat_mult_1:

  1 * n = n

lemma nat_mult_1_right:

  n * 1 = n

Additional theorems about @{term "op ≤"}

lemma less_induct:

  (!!x. (!!y. y < x ==> P y) ==> P x) ==> P a

lemma nat_less_induct:

  (!!n. ∀m<n. P m ==> P n) ==> P n

lemma measure_induct_rule:

  (!!x. (!!y. f y < f x ==> P y) ==> P x) ==> P a

lemma measure_induct:

  (!!x. ∀y. f y < f x --> P y ==> P x) ==> P a

lemma full_nat_induct:

  (!!n. ∀m. Suc m  n --> P m ==> P n) ==> P n

lemma less_Suc_induct:

  [| i < j; !!i. P i (Suc i); !!i j k. [| P i j; P j k |] ==> P i k |] ==> P i j

lemma nat_induct2:

  [| P 0; P (Suc 0); !!k. P k ==> P (Suc (Suc k)) |] ==> P n

lemma infinite_descent:

  (!!n. ¬ P n ==> ∃m<n. ¬ P m) ==> P n

lemma infinite_descent0:

  [| P 0; !!n. [| 0 < n; ¬ P n |] ==> ∃m<n. ¬ P m |] ==> P n

corollary infinite_descent0_measure:

  [| !!x. V x = 0 ==> P x; !!x. [| 0 < V x; ¬ P x |] ==> ∃y. V y < V x ∧ ¬ P y |]
  ==> P x

lemma infinite_descent_measure:

  (!!x. ¬ P x ==> ∃y. V y < V x ∧ ¬ P y) ==> P x

lemma less_mono_imp_le_mono:

  [| !!i j. i < j ==> f i < f j; i  j |] ==> f i  f j

lemma add_le_mono1:

  i  j ==> i + k  j + k

lemma add_le_mono:

  [| i  j; k  l |] ==> i + k  j + l

lemma le_add2:

  n  m + n

lemma le_add1:

  n  n + m

lemma less_add_Suc1:

  i < Suc (i + m)

lemma less_add_Suc2:

  i < Suc (m + i)

lemma less_iff_Suc_add:

  (m < n) = (∃k. n = Suc (m + k))

lemma trans_le_add1:

  i  j ==> i  j + m

lemma trans_le_add2:

  i  j ==> i  m + j

lemma trans_less_add1:

  i < j ==> i < j + m

lemma trans_less_add2:

  i < j ==> i < m + j

lemma add_lessD1:

  i + j < k ==> i < k

lemma not_add_less1:

  ¬ i + j < i

lemma not_add_less2:

  ¬ j + i < i

lemma add_leD1:

  m + k  n ==> m  n

lemma add_leD2:

  m + k  n ==> k  n

lemma add_leE:

  [| m + k  n; [| m  n; k  n |] ==> R |] ==> R

lemma less_add_eq_less:

  [| k < l; m + l = k + n |] ==> m < n

More results about difference

lemma add_diff_inverse:

  ¬ m < n ==> n + (m - n) = m

lemma le_add_diff_inverse:

  n  m ==> n + (m - n) = m

lemma le_add_diff_inverse2:

  n  m ==> m - n + n = m

lemma Suc_diff_le:

  n  m ==> Suc m - n = Suc (m - n)

lemma diff_less_Suc:

  m - n < Suc m

lemma diff_le_self:

  m - n  m

lemma le_iff_add:

  (m  n) = (∃k. n = m + k)

lemma less_imp_diff_less:

  j < k ==> j - n < k

lemma diff_Suc_less:

  0 < n ==> n - Suc i < n

lemma diff_add_assoc:

  k  j ==> i + j - k = i + (j - k)

lemma diff_add_assoc2:

  k  j ==> j + i - k = j - k + i

lemma le_imp_diff_is_add:

  i  j ==> (j - i = k) = (j = k + i)

lemma diff_is_0_eq:

  (m - n = 0) = (m  n)

lemma diff_is_0_eq':

  m  n ==> m - n = 0

lemma zero_less_diff:

  (0 < n - m) = (m < n)

lemma less_imp_add_positive:

  i < j ==> ∃k>0. i + k = j

lemma nat_minus_add_max:

  n - m + m = max n m

lemma nat_diff_split:

  P (a - b) = ((a < b --> P 0) ∧ (∀d. a = b + d --> P d))

lemma nat_diff_split_asm:

  P (a - b) = (¬ (a < b ∧ ¬ P 0 ∨ (∃d. a = b + d ∧ ¬ P d)))

Monotonicity of Multiplication

lemma mult_le_mono1:

  i  j ==> i * k  j * k

lemma mult_le_mono2:

  i  j ==> k * i  k * j

lemma mult_le_mono:

  [| i  j; k  l |] ==> i * k  j * l

lemma mult_less_mono1:

  [| i < j; 0 < k |] ==> i * k < j * k

lemma nat_0_less_mult_iff:

  (0 < m * n) = (0 < m0 < n)

lemma one_le_mult_iff:

  (Suc 0  m * n) = (1  m1  n)

lemma mult_less_cancel2:

  (m * k < n * k) = (0 < km < n)

lemma mult_less_cancel1:

  (k * m < k * n) = (0 < km < n)

lemma mult_le_cancel1:

  (k * m  k * n) = (0 < k --> m  n)

lemma mult_le_cancel2:

  (m * k  n * k) = (0 < k --> m  n)

lemma Suc_mult_less_cancel1:

  (Suc k * m < Suc k * n) = (m < n)

lemma Suc_mult_le_cancel1:

  (Suc k * m  Suc k * n) = (m  n)

lemma le_square:

  m  m * m

lemma le_cube:

  m  m * (m * m)

lemma mult_eq_self_implies_10:

  m = m * n ==> n = 1m = 0

Embedding of the Naturals into any @{text semiring_1}: @{term of_nat}

lemma of_nat_1:

  of_nat 1 = (1::'a)

lemma of_nat_add:

  of_nat (m + n) = of_nat m + of_nat n

lemma of_nat_mult:

  of_nat (m * n) = of_nat m * of_nat n

lemma of_nat_aux_code:

  of_nat_aux 0 i = i
  of_nat_aux (Suc n) i = of_nat_aux n (i + (1::'a))

lemma of_nat_code:

  of_nat n = of_nat_aux n (0::'a)

lemma of_nat_0_eq_iff:

  ((0::'a) = of_nat n) = (0 = n)

lemma of_nat_eq_0_iff:

  (of_nat m = (0::'a)) = (m = 0)

lemma inj_of_nat:

  inj of_nat

lemma zero_le_imp_of_nat:

  (0::'a)  of_nat m

lemma less_imp_of_nat_less:

  m < n ==> of_nat m < of_nat n

lemma of_nat_less_imp_less:

  of_nat m < of_nat n ==> m < n

lemma of_nat_less_iff:

  (of_nat m < of_nat n) = (m < n)

lemma of_nat_le_iff:

  (of_nat m  of_nat n) = (m  n)

lemma of_nat_0_le_iff:

  (0::'a)  of_nat n

lemma of_nat_le_0_iff:

  (of_nat m  (0::'a)) = (m = 0)

lemma of_nat_0_less_iff:

  ((0::'a) < of_nat n) = (0 < n)

lemma of_nat_less_0_iff:

  ¬ of_nat m < (0::'a)

lemma of_nat_diff:

  n  m ==> of_nat (m - n) = of_nat m - of_nat n

lemma abs_of_nat:

  ¦of_nat n¦ = of_nat n

lemma of_nat_id:

  of_nat n = n

lemma of_nat_eq_id:

  of_nat = id

The Set of Natural Numbers

lemma of_nat_in_Nats:

  of_nat nNats

lemma Nats_0:

  (0::'a) ∈ Nats

lemma Nats_1:

  (1::'a) ∈ Nats

lemma Nats_add:

  [| aNats; bNats |] ==> a + bNats

lemma Nats_mult:

  [| aNats; bNats |] ==> a * bNats

Further Arithmetic Facts Concerning the Natural Numbers

lemma subst_equals:

  [| t = s; u = t |] ==> u = s

lemma

  P (a - b) = ((a < b --> P 0) ∧ (∀d. a = b + d --> P d))
  P (min i j) = ((i  j --> P i) ∧ (¬ i  j --> P j))
  P (max i j) = ((i  j --> P j) ∧ (¬ i  j --> P i))

lemma diff_less_mono:

  [| a < b; c  a |] ==> a - c < b - c

lemma less_diff_conv:

  (i < j - k) = (i + k < j)

lemma le_diff_conv:

  (j - k  i) = (j  i + k)

lemma le_diff_conv2:

  k  j ==> (i  j - k) = (i + k  j)

lemma diff_diff_cancel:

  i  n ==> n - (n - i) = i

lemma le_add_diff:

  k  n ==> m  n + m - k

lemma diff_less:

  [| 0 < n; 0 < m |] ==> m - n < m

lemma diff_diff_eq:

  [| k  m; k  n |] ==> m - k - (n - k) = m - n

lemma eq_diff_iff:

  [| k  m; k  n |] ==> (m - k = n - k) = (m = n)

lemma less_diff_iff:

  [| k  m; k  n |] ==> (m - k < n - k) = (m < n)

lemma le_diff_iff:

  [| k  m; k  n |] ==> (m - k  n - k) = (m  n)

lemma diff_le_mono:

  m  n ==> m - l  n - l

lemma diff_le_mono2:

  m  n ==> l - n  l - m

lemma diff_less_mono2:

  [| m < n; m < l |] ==> l - n < l - m

lemma diffs0_imp_equal:

  [| m - n = 0; n - m = 0 |] ==> m = n

lemma min_diff:

  min (m - i) (n - i) = min m n - i

lemma inj_on_diff_nat:

  nN. k  n ==> inj_on (λn. n - k) N

lemma diff_diff_right:

  k  j --> i - (j - k) = i + k - j

lemma diff_Suc_diff_eq1:

  k  j ==> m - Suc (j - k) = m + k - Suc j

lemma diff_Suc_diff_eq2:

  k  j ==> Suc (j - k) - m = Suc j - (k + m)

lemma one_less_mult:

  [| Suc 0 < n; Suc 0 < m |] ==> Suc 0 < m * n

lemma n_less_m_mult_n:

  [| Suc 0 < n; Suc 0 < m |] ==> n < m * n

lemma n_less_n_mult_m:

  [| Suc 0 < n; Suc 0 < m |] ==> n < n * m

lemma inc_induct:

  [| i  j; P j; !!i. [| i < j; P (Suc i) |] ==> P i |] ==> P i

lemma strict_inc_induct:

  [| i < j; !!i. j = Suc i ==> P i; !!i. [| i < j; P (Suc i) |] ==> P i |] ==> P i

lemma zero_induct_lemma:

  [| P k; !!n. P (Suc n) ==> P n |] ==> P (k - i)

lemma zero_induct:

  [| P k; !!n. P (Suc n) ==> P n |] ==> P 0

lemma nat_not_singleton:

  (∀x. x = 0) = False

lemma add_diff_assoc:

  k  j ==> i + (j - k) = i + j - k

lemma add_diff_assoc2:

  k  j ==> j - k + i = j + i - k

size of a datatype value