Theory Nat (Isabelle2005: October 2005)

# Theory Nat

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theory Nat
imports Wellfounded_Recursion Ring_and_Field
uses [Nat.ML]
begin

    (*  Title:      HOL/Nat.thy
        ID:         $Id: Nat.thy,v 1.59 2005/09/28 22:58:55 wenzelm Exp $
        Author:     Tobias Nipkow and Lawrence C Paulson

    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 Wellfounded_Recursion Ring_and_Field
    begin

    subsection {* Type @{text ind} *}

    typedecl ind

    consts
      Zero_Rep      :: ind
      Suc_Rep       :: "ind => ind"

    axioms
      -- {* the axiom of infinity in 2 parts *}
      inj_Suc_Rep:          "inj Suc_Rep"
      Suc_Rep_not_Zero_Rep: "Suc_Rep x ≠ Zero_Rep"
    finalconsts
      Zero_Rep
      Suc_Rep

    subsection {* Type nat *}

    text {* Type definition *}

    consts
      Nat :: "ind set"

    inductive Nat
    intros
      Zero_RepI: "Zero_Rep : Nat"
      Suc_RepI: "i : Nat ==> Suc_Rep i : Nat"

    global

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

    instance nat :: "{ord, zero, one}" ..

    text {* Abstract constants and syntax *}

    consts
      Suc :: "nat => nat"
      pred_nat :: "(nat * nat) set"

    local

    defs
      Zero_nat_def: "0 == Abs_Nat Zero_Rep"
      Suc_def: "Suc == (%n. Abs_Nat (Suc_Rep (Rep_Nat n)))"
      One_nat_def [simp]: "1 == Suc 0"

      -- {* nat operations *}
      pred_nat_def: "pred_nat == {(m, n). n = Suc m}"

      less_def: "m < n == (m, n) : trancl pred_nat"

      le_def: "m ≤ (n::nat) == ~ (n < m)"

    text {* Induction *}

    theorem 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 Nat.induct])
      apply (iprover elim: Abs_Nat_inverse [THEN subst])
      done

    text {* Distinctness of constructors *}

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

    text {* Injectiveness of @{term Suc} *}

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

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

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

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

    text {* @{typ nat} is a datatype *}

    rep_datatype nat
      distinct  Suc_not_Zero Zero_not_Suc
      inject    Suc_Suc_eq
      induction nat_induct

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

    lemma Suc_n_not_n: "Suc t ≠ t"
      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"} *}

    theorem 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 {* Basic properties of "less than" *}

    lemma wf_pred_nat: "wf pred_nat"
      apply (unfold wf_def pred_nat_def, clarify)
      apply (induct_tac x, blast+)
      done

    lemma wf_less: "wf {(x, y::nat). x < y}"
      apply (unfold less_def)
      apply (rule wf_pred_nat [THEN wf_trancl, THEN wf_subset], blast)
      done

    lemma less_eq: "((m, n) : pred_nat^+) = (m < n)"
      apply (unfold less_def)
      apply (rule refl)
      done

    subsubsection {* Introduction properties *}

    lemma less_trans: "i < j ==> j < k ==> i < (k::nat)"
      apply (unfold less_def)
      apply (rule trans_trancl [THEN transD], assumption+)
      done

    lemma lessI [iff]: "n < Suc n"
      apply (unfold less_def pred_nat_def)
      apply (simp add: r_into_trancl)
      done

    lemma less_SucI: "i < j ==> i < Suc j"
      apply (rule less_trans, assumption)
      apply (rule lessI)
      done

    lemma zero_less_Suc [iff]: "0 < Suc n"
      apply (induct n)
      apply (rule lessI)
      apply (erule less_trans)
      apply (rule lessI)
      done

    subsubsection {* Elimination properties *}

    lemma less_not_sym: "n < m ==> ~ m < (n::nat)"
      apply (unfold less_def)
      apply (blast intro: wf_pred_nat wf_trancl [THEN wf_asym])
      done

    lemma less_asym:
      assumes h1: "(n::nat) < m" and h2: "~ P ==> m < n" shows P
      apply (rule contrapos_np)
      apply (rule less_not_sym)
      apply (rule h1)
      apply (erule h2)
      done

    lemma less_not_refl: "~ n < (n::nat)"
      apply (unfold less_def)
      apply (rule wf_pred_nat [THEN wf_trancl, THEN wf_not_refl])
      done

    lemma less_irrefl [elim!]: "(n::nat) < n ==> R"
      by (rule notE, rule less_not_refl)

    lemma less_not_refl2: "n < m ==> m ≠ (n::nat)" by blast

    lemma less_not_refl3: "(s::nat) < t ==> s ≠ t"
      by (rule not_sym, rule less_not_refl2)

    lemma lessE:
      assumes major: "i < k"
      and p1: "k = Suc i ==> P" and p2: "!!j. i < j ==> k = Suc j ==> P"
      shows P
      apply (rule major [unfolded less_def pred_nat_def, THEN tranclE], simp_all)
      apply (erule p1)
      apply (rule p2)
      apply (simp add: less_def pred_nat_def, assumption)
      done

    lemma not_less0 [iff]: "~ n < (0::nat)"
      by (blast elim: lessE)

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

    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 less_Suc_eq: "(m < Suc n) = (m < n | m = n)"
      by (blast elim!: less_SucE intro: less_trans)

    lemma less_one [iff]: "(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 (induct n) (fast elim: less_trans lessE)+

    text {* "Less than" is a linear ordering *}
    lemma less_linear: "m < n | m = n | n < (m::nat)"
      apply (induct m)
      apply (induct n)
      apply (rule refl [THEN disjI1, THEN disjI2])
      apply (rule zero_less_Suc [THEN disjI1])
      apply (blast intro: Suc_mono less_SucI elim: lessE)
      done

    text {* "Less than" is antisymmetric, sort of *}
    lemma less_antisym: "[| ¬ n < m; n < Suc m |] ==> m = n"
    apply(simp only:less_Suc_eq)
    apply blast
    done

    lemma nat_neq_iff: "((m::nat) ≠ n) = (m < n | n < m)"
      using less_linear by blast

    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"
      apply (simp add: nat_neq_iff)
      apply (blast elim!: less_irrefl less_SucE elim: less_asym)
      done

    lemma Suc_lessD: "Suc m < n ==> m < n"
      apply (induct n)
      apply (fast intro!: lessI [THEN less_SucI] elim: less_trans lessE)+
      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 (blast elim: lessE dest: Suc_lessD)

    lemma Suc_less_eq [iff, code]: "(Suc m < Suc n) = (m < n)"
      apply (rule iffI)
      apply (erule Suc_less_SucD)
      apply (erule Suc_mono)
      done

    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

    lemma [code]: "((n::nat) < 0) = False" by simp
    lemma [code]: "(0 < Suc n) = True" by simp

    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)"
    by (rule_tac m = m and n = n in diff_induct, simp_all)

    text {* Complete induction, aka course-of-values induction *}
    lemma nat_less_induct:
      assumes prem: "!!n. ∀m::nat. m < n --> P m ==> P n" shows "P n"
      apply (rule_tac a=n in wf_induct)
      apply (rule wf_pred_nat [THEN wf_trancl])
      apply (rule prem)
      apply (unfold less_def, assumption)
      done

    lemmas less_induct = nat_less_induct [rule_format, case_names less]

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

    text {* Was @{text le_eq_less_Suc}, but this orientation is more useful *}
    lemma less_Suc_eq_le: "(m < Suc n) = (m ≤ n)"
      by (unfold le_def, rule not_less_eq [symmetric])

    lemma le_imp_less_Suc: "m ≤ n ==> m < Suc n"
      by (rule less_Suc_eq_le [THEN iffD2])

    lemma le0 [iff]: "(0::nat) ≤ n"
      by (unfold le_def, rule not_less0)

    lemma Suc_n_not_le_n: "~ Suc n ≤ n"
      by (simp add: le_def)

    lemma le_0_eq [iff]: "((i::nat) ≤ 0) = (i = 0)"
      by (induct i) (simp_all add: le_def)

    lemma le_Suc_eq: "(m ≤ Suc n) = (m ≤ n | m = Suc n)"
      by (simp del: less_Suc_eq_le 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"
      apply (simp add: le_def less_Suc_eq)
      apply (blast elim!: less_irrefl less_asym)
      done -- {* formerly called lessD *}

    lemma Suc_leD: "Suc(m) ≤ n ==> m ≤ n"
      by (simp add: le_def less_Suc_eq)

    text {* Stronger version of @{text Suc_leD} *}
    lemma Suc_le_lessD: "Suc m ≤ n ==> m < n"
      apply (simp add: le_def less_Suc_eq)
      using less_linear
      apply blast
      done

    lemma Suc_le_eq: "(Suc m ≤ n) = (m < n)"
      by (blast intro: Suc_leI Suc_le_lessD)

    lemma le_SucI: "m ≤ n ==> m ≤ Suc n"
      by (unfold le_def) (blast dest: Suc_lessD)

    lemma less_imp_le: "m < n ==> m ≤ (n::nat)"
      by (unfold le_def) (blast elim: less_asym)

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

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

    lemma le_imp_less_or_eq: "m ≤ n ==> m < n | m = (n::nat)"
      apply (unfold le_def)
      using less_linear
      apply (blast elim: less_irrefl less_asym)
      done

    lemma less_or_eq_imp_le: "m < n | m = n ==> m ≤ (n::nat)"
      apply (unfold le_def)
      using less_linear
      apply (blast elim!: less_irrefl elim: less_asym)
      done

    lemma le_eq_less_or_eq: "(m ≤ (n::nat)) = (m < n | m=n)"
      by (iprover intro: less_or_eq_imp_le le_imp_less_or_eq)

    text {* Useful with @{text Blast}. *}
    lemma eq_imp_le: "(m::nat) = n ==> m ≤ n"
      by (rule less_or_eq_imp_le, rule disjI2)

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

    lemma le_less_trans: "[| i ≤ j; j < k |] ==> i < (k::nat)"
      by (blast dest!: le_imp_less_or_eq intro: less_trans)

    lemma less_le_trans: "[| i < j; j ≤ k |] ==> i < (k::nat)"
      by (blast dest!: le_imp_less_or_eq intro: less_trans)

    lemma le_trans: "[| i ≤ j; j ≤ k |] ==> i ≤ (k::nat)"
      by (blast dest!: le_imp_less_or_eq intro: less_or_eq_imp_le less_trans)

    lemma le_anti_sym: "[| m ≤ n; n ≤ m |] ==> m = (n::nat)"
      by (blast dest!: le_imp_less_or_eq elim!: less_irrefl elim: less_asym)

    lemma Suc_le_mono [iff]: "(Suc n ≤ Suc m) = (n ≤ m)"
      by (simp add: le_simps)

    text {* Axiom @{text order_less_le} of class @{text order}: *}
    lemma nat_less_le: "((m::nat) < n) = (m ≤ n & m ≠ n)"
      by (simp add: le_def nat_neq_iff) (blast elim!: less_asym)

    lemma le_neq_implies_less: "(m::nat) ≤ n ==> m ≠ n ==> m < n"
      by (rule iffD2, rule nat_less_le, rule conjI)

    text {* Axiom @{text linorder_linear} of class @{text linorder}: *}
    lemma nat_le_linear: "(m::nat) ≤ n | n ≤ m"
      apply (simp add: le_eq_less_or_eq)
      using less_linear
      apply blast
      done

    text {* Type {@typ nat} is a wellfounded linear order *}

    instance nat :: "{order, linorder, wellorder}"
      by intro_classes
        (assumption |
          rule le_refl le_trans le_anti_sym nat_less_le nat_le_linear wf_less)+

    lemmas linorder_neqE_nat = linorder_neqE[where 'a = nat]

    lemma not_less_less_Suc_eq: "~ n < m ==> (n < Suc m) = (n = m)"
      by (blast elim!: less_SucE)

    text {*
      Rewrite @{term "n < Suc m"} to @{term "n = m"}
      if @{term "~ n < m"} or @{term "m ≤ n"} hold.
      Not suitable as default simprules because they often lead to looping
    *}
    lemma le_less_Suc_eq: "m ≤ n ==> (n < Suc m) = (n = m)"
      by (rule not_less_less_Suc_eq, rule leD)

    lemmas not_less_simps = not_less_less_Suc_eq le_less_Suc_eq

    text {*
      Re-orientation of the equations @{text "0 = x"} and @{text "1 = x"}.
      No longer added as simprules (they loop)
      but via @{text reorient_simproc} in Bin
    *}

    text {* Polymorphic, not just for @{typ nat} *}
    lemma zero_reorient: "(0 = x) = (x = 0)"
      by auto

    lemma one_reorient: "(1 = x) = (x = 1)"
      by auto

    subsection {* Arithmetic operators *}

    axclass power < type

    consts
      power :: "('a::power) => nat => 'a"            (infixr "^" 80)

    text {* arithmetic operators @{text "+ -"} and @{text "*"} *}

    instance nat :: "{plus, minus, times, power}" ..

    text {* size of a datatype value; overloaded *}
    consts size :: "'a => nat"

    primrec
      add_0:    "0 + n = n"
      add_Suc:  "Suc m + n = Suc (m + n)"

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

    primrec
      mult_0:   "0 * n = 0"
      mult_Suc: "Suc m * n = n + (m * n)"

    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 (case_tac n) simp_all

    lemma gr_implies_not0: "!!n::nat. m<n ==> n ≠ 0"
      by (case_tac n) simp_all

    lemma neq0_conv [iff]: "!!n::nat. (n ≠ 0) = (0 < n)"
      by (case_tac n) simp_all

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

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

    lemma not_gr0 [iff]: "!!n::nat. (~ (0 < n)) = (n = 0)"
      apply (rule iffI)
      apply (rule ccontr, simp_all)
      done

    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 (case_tac m) simp_all

    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

    subsection {* @{text LEAST} theorems for type @{typ nat}*}

    lemma Least_Suc:
         "[| P n; ~ P 0 |] ==> (LEAST n. P n) = Suc (LEAST m. P(Suc m))"
      apply (case_tac "n", auto)
      apply (frule LeastI)
      apply (drule_tac P = "%x. P (Suc x) " in LeastI)
      apply (subgoal_tac " (LEAST x. P x) ≤ Suc (LEAST x. P (Suc x))")
      apply (erule_tac [2] Least_le)
      apply (case_tac "LEAST x. P x", auto)
      apply (drule_tac P = "%x. P (Suc x) " in Least_le)
      apply (blast intro: order_antisym)
      done

    lemma Least_Suc2:
         "[|P n; Q m; ~P 0; !k. P (Suc k) = Q k|] ==> Least P = Suc (Least Q)"
      by (erule (1) Least_Suc [THEN ssubst], simp)

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

    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: min_of_mono)

    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: max_of_mono)

    subsection {* Basic rewrite rules for the arithmetic operators *}

    text {* Difference *}

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

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

    text {*
      Could be (and is, below) generalized in various ways
      However, none of the generalizations are currently in the simpset,
      and I dread to think what happens if I put them in
    *}
    lemma Suc_pred [simp]: "0 < n ==> Suc (n - Suc 0) = n"
      by (simp split add: nat.split)

    declare diff_Suc [simp del, code del]

    subsection {* Addition *}

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

    text {* Associative law for addition *}
    lemma nat_add_assoc: "(m + n) + k = m + ((n + k)::nat)"
      by (induct m) simp_all

    text {* Commutative law for addition *}
    lemma nat_add_commute: "m + n = n + (m::nat)"
      by (induct m) simp_all

    lemma nat_add_left_commute: "x + (y + z) = y + ((x + z)::nat)"
      apply (rule mk_left_commute [of "op +"])
      apply (rule nat_add_assoc)
      apply (rule nat_add_commute)
      done

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

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

    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

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

    lemma add_is_0 [iff]: "!!m::nat. (m + n = 0) = (m = 0 & n = 0)"
      by (case_tac m) simp_all

    lemma add_is_1: "(m+n= Suc 0) = (m= Suc 0 & n=0 | m=0 & n= Suc 0)"
      by (case_tac 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_gr_0 [iff]: "!!m::nat. (0 < m + n) = (0 < m | 0 < n)"
      by (simp del: neq0_conv add: neq0_conv [symmetric])

    lemma add_eq_self_zero: "!!m::nat. m + n = m ==> n = 0"
      apply (drule add_0_right [THEN ssubst])
      apply (simp add: nat_add_assoc del: add_0_right)
      done

    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

    subsection {* Multiplication *}

    text {* right annihilation in product *}
    lemma mult_0_right [simp]: "(m::nat) * 0 = 0"
      by (induct m) simp_all

    text {* right successor law for multiplication *}
    lemma mult_Suc_right [simp]: "m * Suc n = m + (m * n)"
      by (induct m) (simp_all add: nat_add_left_commute)

    text {* Commutative law for multiplication *}
    lemma nat_mult_commute: "m * n = n * (m::nat)"
      by (induct m) simp_all

    text {* addition distributes over multiplication *}
    lemma add_mult_distrib: "(m + n) * k = (m * k) + ((n * k)::nat)"
      by (induct m) (simp_all add: nat_add_assoc nat_add_left_commute)

    lemma add_mult_distrib2: "k * (m + n) = (k * m) + ((k * n)::nat)"
      by (induct m) (simp_all add: nat_add_assoc)

    text {* Associative law for multiplication *}
    lemma nat_mult_assoc: "(m * n) * k = m * ((n * k)::nat)"
      by (induct m) (simp_all add: add_mult_distrib)

    text{*The naturals form a @{text comm_semiring_1_cancel}*}
    instance nat :: comm_semiring_1_cancel
    proof
      fix i j k :: nat
      show "(i + j) + k = i + (j + k)" by (rule nat_add_assoc)
      show "i + j = j + i" by (rule nat_add_commute)
      show "0 + i = i" by simp
      show "(i * j) * k = i * (j * k)" by (rule nat_mult_assoc)
      show "i * j = j * i" by (rule nat_mult_commute)
      show "1 * i = i" by simp
      show "(i + j) * k = i * k + j * k" by (simp add: add_mult_distrib)
      show "0 ≠ (1::nat)" by simp
      assume "k+i = k+j" thus "i=j" by simp
    qed

    lemma mult_is_0 [simp]: "((m::nat) * n = 0) = (m=0 | n=0)"
      apply (induct m)
      apply (induct_tac [2] n, simp_all)
      done

    subsection {* Monotonicity of Addition *}

    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 (erule_tac m1 = 0 in less_imp_Suc_add [THEN exE], simp)
      apply (induct_tac x)
      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

    subsection {* Additional theorems about "less than" *}

    text {* A [clumsy] way of lifting @{text "<"}
      monotonicity to @{text "≤"} monotonicity *}
    lemma less_mono_imp_le_mono:
      assumes lt_mono: "!!i j::nat. i < j ==> f i < f j"
      and le: "i ≤ j" shows "f i ≤ ((f j)::nat)" using le
      apply (simp add: order_le_less)
      apply (blast intro!: lt_mono)
      done

    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 (erule add_lessD1 [THEN less_irrefl])
      done

    lemma not_add_less2 [iff]: "~ (j + i < (i::nat))"
      by (simp add: add_commute not_add_less1)

    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)

    subsection {* Difference *}

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

    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: le_add_diff_inverse add_commute)

    subsection {* More results about difference *}

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

    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_Suc_less [simp]: "0<n ==> n - Suc i < n"
      apply (case_tac "n", safe)
      apply (simp add: le_simps)
      done

    text {* This and the next few suggested by Florian Kammueller *}
    lemma diff_commute: "(i::nat) - j - k = i - k - j"
      by (simp add: diff_diff_left add_commute)

    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 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_assoc)

    lemma le_imp_diff_is_add: "i ≤ (j::nat) ==> (j - i = k) = (j = k + i)"
      apply safe
      apply (simp_all add: diff_add_inverse2)
      done

    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: "i < j  ==> ∃k::nat. 0 < k & i + k = j"
      apply (rule_tac x = "j - i" in exI)
      apply (simp (no_asm_simp) add: add_diff_inverse less_not_sym)
      done

    lemma zero_induct_lemma: "P k ==> (!!n. P (Suc n) ==> P n) ==> P (k - i)"
      apply (induct k i rule: diff_induct)
      apply (simp_all (no_asm))
      apply iprover
      done

    lemma zero_induct: "P k ==> (!!n. P (Suc n) ==> P n) ==> P 0"
      apply (rule diff_self_eq_0 [THEN subst])
      apply (rule zero_induct_lemma, iprover+)
      done

    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 *}

    lemmas nat_distrib =
      add_mult_distrib add_mult_distrib2 diff_mult_distrib diff_mult_distrib2

    subsection {* 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 (case_tac [2] n, simp_all)
      done

    lemma one_le_mult_iff [simp]: "(Suc 0 ≤ m * n) = (1 ≤ m & 1 ≤ n)"
      apply (induct m)
      apply (case_tac [2] n, simp_all)
      done

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

    lemma one_eq_mult_iff [simp]: "(Suc 0 = m * n) = (m = 1 & n = 1)"
      apply (rule trans)
      apply (rule_tac [2] mult_eq_1_iff, fastsimp)
      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 mult_cancel2 [simp]: "(m * k = n * k) = (m = n | (k = (0::nat)))"
      apply (cut_tac less_linear, safe, auto)
      apply (drule mult_less_mono1, assumption, simp)+
      done

    lemma mult_cancel1 [simp]: "(k * m = k * n) = (m = n | (k = (0::nat)))"
      by (simp add: mult_commute [of k])

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

    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 (fastsimp elim!: less_SucE)
      apply (fastsimp dest: mult_less_mono2)
      done

    end

### Type @{text ind}

### Type nat

theorem 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 Suc_neq_Zero:

      Suc m = 0 ==> R

lemma Zero_neq_Suc:

      0 = Suc m ==> R

lemma inj_Suc:

      inj_on Suc N

lemma Suc_inject:

      Suc x = Suc y ==> x = y

lemma Suc_Suc_eq:

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

lemma nat_not_singleton:

      (∀x. x = 0) = False

lemma n_not_Suc_n:

      n ≠ Suc n

lemma Suc_n_not_n:

      Suc t ≠ t

theorem diff_induct:

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

### Basic properties of "less than"

lemma wf_pred_nat:

      wf pred_nat

lemma wf_less:

      wf {(x, y). x < y}

lemma less_eq:

      ((m, n) ∈ pred_nat+) = (m < n)

#### Introduction properties

lemma less_trans:

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

lemma lessI:

      n < Suc n

lemma less_SucI:

      i < j ==> i < Suc j

lemma zero_less_Suc:

      0 < Suc n

#### Elimination properties

lemma less_not_sym:

      n < m ==> ¬ m < n

lemma less_asym:

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

lemma less_not_refl:

      ¬ n < n

lemma less_irrefl:

      n < n ==> R

lemma less_not_refl2:

      n < m ==> m ≠ n

lemma less_not_refl3:

      s < t ==> s ≠ t

lemma lessE:

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

lemma not_less0:

      ¬ n < 0

lemma less_zeroE:

      n < 0 ==> R

lemma less_SucE:

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

lemma less_Suc_eq:

      (m < Suc n) = (m < n ∨ m = 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_linear:

      m < n ∨ m = n ∨ n < m

lemma less_antisym:

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

lemma nat_neq_iff:

      (m ≠ n) = (m < n ∨ n < 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 Suc_lessD:

      Suc m < n ==> m < n

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 Suc_less_eq:

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

lemma less_trans_Suc:

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

lemma

      (n < 0) = False

lemma

      (0 < Suc n) = True

lemma not_less_eq:

      (¬ m < n) = (n < Suc m)

lemma nat_less_induct:

      (!!n. ∀m<n. P m ==> P n) ==> P n

lemmas less_induct:

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

lemmas less_induct:

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

### Properties of "less than or equal"

lemma less_Suc_eq_le:

      (m < Suc n) = (m ≤ n)

lemma le_imp_less_Suc:

      m ≤ n ==> m < Suc n

lemma le0:

      0 ≤ n

lemma Suc_n_not_le_n:

      ¬ Suc n ≤ n

lemma le_0_eq:

      (i ≤ 0) = (i = 0)

lemma le_Suc_eq:

      (m ≤ Suc n) = (m ≤ n ∨ m = 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_leD:

      Suc m ≤ n ==> m ≤ n

lemma Suc_le_lessD:

      Suc m ≤ n ==> m < n

lemma Suc_le_eq:

      (Suc m ≤ n) = (m < n)

lemma le_SucI:

      m ≤ n ==> m ≤ Suc n

lemma less_imp_le:

      m < n ==> m ≤ n

lemmas le_simps:

      m < n ==> m ≤ n

      (m < Suc n) = (m ≤ n)

      (Suc m ≤ n) = (m < n)

lemmas le_simps:

      m < n ==> m ≤ n

      (m < Suc n) = (m ≤ n)

      (Suc m ≤ n) = (m < n)

lemma le_imp_less_or_eq:

      m ≤ n ==> m < n ∨ m = n

lemma less_or_eq_imp_le:

      m < n ∨ m = n ==> m ≤ n

lemma le_eq_less_or_eq:

      (m ≤ n) = (m < n ∨ m = n)

lemma eq_imp_le:

      m = n ==> m ≤ n

lemma le_refl:

      n ≤ n

lemma le_less_trans:

      [| i ≤ j; j < k |] ==> i < k

lemma less_le_trans:

      [| i < j; j ≤ k |] ==> i < k

lemma le_trans:

      [| i ≤ j; j ≤ k |] ==> i ≤ k

lemma le_anti_sym:

      [| m ≤ n; n ≤ m |] ==> m = n

lemma Suc_le_mono:

      (Suc n ≤ Suc m) = (n ≤ m)

lemma nat_less_le:

      (m < n) = (m ≤ n ∧ m ≠ n)

lemma le_neq_implies_less:

      [| m ≤ n; m ≠ n |] ==> m < n

lemma nat_le_linear:

      m ≤ n ∨ n ≤ m

lemmas linorder_neqE_nat:

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

lemmas linorder_neqE_nat:

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

lemma not_less_less_Suc_eq:

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

lemma le_less_Suc_eq:

      m ≤ n ==> (n < Suc m) = (n = m)

lemmas not_less_simps:

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

      m ≤ n ==> (n < Suc m) = (n = m)

lemmas not_less_simps:

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

      m ≤ n ==> (n < Suc m) = (n = m)

lemma zero_reorient:

      ((0::'a) = x) = (x = (0::'a))

lemma one_reorient:

      ((1::'a) = x) = (x = (1::'a))

### Arithmetic operators

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 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 j ∧ j < n))

lemma nat_induct2:

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

### @{text LEAST} theorems for type @{typ nat}

lemma Least_Suc:

      [| P n; ¬ P 0 |] ==> (LEAST n. P n) = Suc (LEAST m. P (Suc m))

lemma Least_Suc2:

      [| P n; Q m; ¬ P 0; ∀k. P (Suc k) = Q k |] ==> Least P = Suc (Least Q)

### @{term min} and @{term max}

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 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)

### Basic rewrite rules for the arithmetic operators

lemma diff_0_eq_0:

      0 - n = 0

lemma diff_Suc_Suc:

      Suc m - Suc n = m - n

lemma Suc_pred:

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

### Addition

lemma add_0_right:

      m + 0 = m

lemma add_Suc_right:

      m + Suc n = Suc (m + n)

lemma

      Suc m + n = m + Suc n

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 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_is_0:

      (m + n = 0) = (m = 0 ∧ n = 0)

lemma add_is_1:

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

lemma one_is_add:

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

lemma add_gr_0:

      (0 < m + n) = (0 < m ∨ 0 < n)

lemma add_eq_self_zero:

      m + n = m ==> n = 0

lemma inj_on_add_nat:

      inj_on (%n. n + k) N

### Multiplication

lemma mult_0_right:

      m * 0 = 0

lemma mult_Suc_right:

      m * Suc n = m + m * n

lemma nat_mult_commute:

      m * n = n * m

lemma add_mult_distrib:

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

lemma add_mult_distrib2:

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

lemma nat_mult_assoc:

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

lemma mult_is_0:

      (m * n = 0) = (m = 0 ∨ n = 0)

### Monotonicity of Addition

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 "less than"

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

### Difference

lemma diff_self_eq_0:

      m - m = 0

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

### More results about difference

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 less_imp_diff_less:

      j < k ==> j - n < k

lemma diff_diff_left:

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

lemma Suc_diff_diff:

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

lemma diff_Suc_less:

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

lemma diff_commute:

      i - j - k = i - k - j

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 diff_add_inverse:

      n + m - n = m

lemma diff_add_inverse2:

      m + n - n = m

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 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 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

lemmas 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

lemmas 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

### 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 < m ∧ 0 < n)

lemma one_le_mult_iff:

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

lemma mult_eq_1_iff:

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

lemma one_eq_mult_iff:

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

lemma mult_less_cancel2:

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

lemma mult_less_cancel1:

      (k * m < k * n) = (0 < k ∧ m < 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 mult_cancel2:

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

lemma mult_cancel1:

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

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 Suc_mult_cancel1:

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

lemma mult_eq_self_implies_10:

      m = m * n ==> n = 1 ∨ m = 0

theorem nat_rec_0:

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

theorem nat_rec_Suc:

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

theorem nat_case_0:

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

theorem nat_case_Suc:

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