# Theory IntDiv

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theory IntDiv
imports SetInterval Recdef
uses (IntDiv_setup.ML)
begin

    (*  Title:      HOL/IntDiv.thy
        ID:         $Id: IntDiv.thy,v 1.39 2005/09/20 12:03:37 wenzelm Exp $
        Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
        Copyright   1999  University of Cambridge

    *)

    header{*The Division Operators div and mod; the Divides Relation dvd*}

    theory IntDiv
    imports SetInterval Recdef
    uses ("IntDiv_setup.ML")
    begin

    declare zless_nat_conj [simp]

    constdefs
      quorem :: "(int*int) * (int*int) => bool"
        --{*definition of quotient and remainder*}
        "quorem == %((a,b), (q,r)).
                          a = b*q + r &
                          (if 0 < b then 0≤r & r<b else b<r & r ≤ 0)"

      adjust :: "[int, int*int] => int*int"
        --{*for the division algorithm*}
        "adjust b == %(q,r). if 0 ≤ r-b then (2*q + 1, r-b)
                             else (2*q, r)"

    text{*algorithm for the case @{text "a≥0, b>0"}*}
    consts posDivAlg :: "int*int => int*int"
    recdef posDivAlg "measure (%(a,b). nat(a - b + 1))"
        "posDivAlg (a,b) =
           (if (a<b | b≤0) then (0,a)
            else adjust b (posDivAlg(a, 2*b)))"

    text{*algorithm for the case @{text "a<0, b>0"}*}
    consts negDivAlg :: "int*int => int*int"
    recdef negDivAlg "measure (%(a,b). nat(- a - b))"
        "negDivAlg (a,b) =
           (if (0≤a+b | b≤0) then (-1,a+b)
            else adjust b (negDivAlg(a, 2*b)))"

    text{*algorithm for the general case @{term "b≠0"}*}
    constdefs
      negateSnd :: "int*int => int*int"
        "negateSnd == %(q,r). (q,-r)"

      divAlg :: "int*int => int*int"
        --{*The full division algorithm considers all possible signs for a, b
           including the special case @{text "a=0, b<0"} because
           @{term negDivAlg} requires @{term "a<0"}.*}
        "divAlg ==
           %(a,b). if 0≤a then
                      if 0≤b then posDivAlg (a,b)
                      else if a=0 then (0,0)
                           else negateSnd (negDivAlg (-a,-b))
                   else
                      if 0<b then negDivAlg (a,b)
                      else         negateSnd (posDivAlg (-a,-b))"

    instance
      int :: "Divides.div" ..       --{*avoid clash with 'div' token*}

    text{*The operators are defined with reference to the algorithm, which is
    proved to satisfy the specification.*}
    defs
      div_def:   "a div b == fst (divAlg (a,b))"
      mod_def:   "a mod b == snd (divAlg (a,b))"

    text{*
    Here is the division algorithm in ML:

    \begin{verbatim}
        fun posDivAlg (a,b) =
          if a<b then (0,a)
          else let val (q,r) = posDivAlg(a, 2*b)
                   in  if 0≤r-b then (2*q+1, r-b) else (2*q, r)
               end

        fun negDivAlg (a,b) =
          if 0≤a+b then (~1,a+b)
          else let val (q,r) = negDivAlg(a, 2*b)
                   in  if 0≤r-b then (2*q+1, r-b) else (2*q, r)
               end;

        fun negateSnd (q,r:int) = (q,~r);

        fun divAlg (a,b) = if 0≤a then
                              if b>0 then posDivAlg (a,b)
                               else if a=0 then (0,0)
                                    else negateSnd (negDivAlg (~a,~b))
                           else
                              if 0<b then negDivAlg (a,b)
                              else        negateSnd (posDivAlg (~a,~b));
    \end{verbatim}
    *}

    subsection{*Uniqueness and Monotonicity of Quotients and Remainders*}

    lemma unique_quotient_lemma:
         "[| b*q' + r'  ≤ b*q + r;  0 ≤ r';  r' < b;  r < b |]
          ==> q' ≤ (q::int)"
    apply (subgoal_tac "r' + b * (q'-q) ≤ r")
     prefer 2 apply (simp add: right_diff_distrib)
    apply (subgoal_tac "0 < b * (1 + q - q') ")
    apply (erule_tac [2] order_le_less_trans)
     prefer 2 apply (simp add: right_diff_distrib right_distrib)
    apply (subgoal_tac "b * q' < b * (1 + q) ")
     prefer 2 apply (simp add: right_diff_distrib right_distrib)
    apply (simp add: mult_less_cancel_left)
    done

    lemma unique_quotient_lemma_neg:
         "[| b*q' + r' ≤ b*q + r;  r ≤ 0;  b < r;  b < r' |]
          ==> q ≤ (q'::int)"
    by (rule_tac b = "-b" and r = "-r'" and r' = "-r" in unique_quotient_lemma,
        auto)

    lemma unique_quotient:
         "[| quorem ((a,b), (q,r));  quorem ((a,b), (q',r'));  b ≠ 0 |]
          ==> q = q'"
    apply (simp add: quorem_def linorder_neq_iff split: split_if_asm)
    apply (blast intro: order_antisym
                 dest: order_eq_refl [THEN unique_quotient_lemma]
                 order_eq_refl [THEN unique_quotient_lemma_neg] sym)+
    done

    lemma unique_remainder:
         "[| quorem ((a,b), (q,r));  quorem ((a,b), (q',r'));  b ≠ 0 |]
          ==> r = r'"
    apply (subgoal_tac "q = q'")
     apply (simp add: quorem_def)
    apply (blast intro: unique_quotient)
    done

    subsection{*Correctness of @{term posDivAlg}, the Algorithm for Non-Negative Dividends*}

    text{*And positive divisors*}

    lemma adjust_eq [simp]:
         "adjust b (q,r) =
          (let diff = r-b in
            if 0 ≤ diff then (2*q + 1, diff)
                         else (2*q, r))"
    by (simp add: Let_def adjust_def)

    declare posDivAlg.simps [simp del]

    text{*use with a simproc to avoid repeatedly proving the premise*}
    lemma posDivAlg_eqn:
         "0 < b ==>
          posDivAlg (a,b) = (if a<b then (0,a) else adjust b (posDivAlg(a, 2*b)))"
    by (rule posDivAlg.simps [THEN trans], simp)

    text{*Correctness of @{term posDivAlg}: it computes quotients correctly*}
    theorem posDivAlg_correct [rule_format]:
         "0 ≤ a --> 0 < b --> quorem ((a, b), posDivAlg (a, b))"
    apply (induct_tac a b rule: posDivAlg.induct, auto)
     apply (simp_all add: quorem_def)
     (*base case: a<b*)
     apply (simp add: posDivAlg_eqn)
    (*main argument*)
    apply (subst posDivAlg_eqn, simp_all)
    apply (erule splitE)
    apply (auto simp add: right_distrib Let_def)
    done

    subsection{*Correctness of @{term negDivAlg}, the Algorithm for Negative Dividends*}

    text{*And positive divisors*}

    declare negDivAlg.simps [simp del]

    text{*use with a simproc to avoid repeatedly proving the premise*}
    lemma negDivAlg_eqn:
         "0 < b ==>
          negDivAlg (a,b) =
           (if 0≤a+b then (-1,a+b) else adjust b (negDivAlg(a, 2*b)))"
    by (rule negDivAlg.simps [THEN trans], simp)

    (*Correctness of negDivAlg: it computes quotients correctly
      It doesn't work if a=0 because the 0/b equals 0, not -1*)
    lemma negDivAlg_correct [rule_format]:
         "a < 0 --> 0 < b --> quorem ((a, b), negDivAlg (a, b))"
    apply (induct_tac a b rule: negDivAlg.induct, auto)
     apply (simp_all add: quorem_def)
     (*base case: 0≤a+b*)
     apply (simp add: negDivAlg_eqn)
    (*main argument*)
    apply (subst negDivAlg_eqn, assumption)
    apply (erule splitE)
    apply (auto simp add: right_distrib Let_def)
    done

    subsection{*Existence Shown by Proving the Division Algorithm to be Correct*}

    (*the case a=0*)
    lemma quorem_0: "b ≠ 0 ==> quorem ((0,b), (0,0))"
    by (auto simp add: quorem_def linorder_neq_iff)

    lemma posDivAlg_0 [simp]: "posDivAlg (0, b) = (0, 0)"
    by (subst posDivAlg.simps, auto)

    lemma negDivAlg_minus1 [simp]: "negDivAlg (-1, b) = (-1, b - 1)"
    by (subst negDivAlg.simps, auto)

    lemma negateSnd_eq [simp]: "negateSnd(q,r) = (q,-r)"
    by (simp add: negateSnd_def)

    lemma quorem_neg: "quorem ((-a,-b), qr) ==> quorem ((a,b), negateSnd qr)"
    by (auto simp add: split_ifs quorem_def)

    lemma divAlg_correct: "b ≠ 0 ==> quorem ((a,b), divAlg(a,b))"
    by (force simp add: linorder_neq_iff quorem_0 divAlg_def quorem_neg
                        posDivAlg_correct negDivAlg_correct)

    text{*Arbitrary definitions for division by zero.  Useful to simplify
        certain equations.*}

    lemma DIVISION_BY_ZERO [simp]: "a div (0::int) = 0 & a mod (0::int) = a"
    by (simp add: div_def mod_def divAlg_def posDivAlg.simps)

    text{*Basic laws about division and remainder*}

    lemma zmod_zdiv_equality: "(a::int) = b * (a div b) + (a mod b)"
    apply (case_tac "b = 0", simp)
    apply (cut_tac a = a and b = b in divAlg_correct)
    apply (auto simp add: quorem_def div_def mod_def)
    done

    lemma zdiv_zmod_equality: "(b * (a div b) + (a mod b)) + k = (a::int)+k"
    by(simp add: zmod_zdiv_equality[symmetric])

    lemma zdiv_zmod_equality2: "((a div b) * b + (a mod b)) + k = (a::int)+k"
    by(simp add: mult_commute zmod_zdiv_equality[symmetric])

    use "IntDiv_setup.ML"

    lemma pos_mod_conj : "(0::int) < b ==> 0 ≤ a mod b & a mod b < b"
    apply (cut_tac a = a and b = b in divAlg_correct)
    apply (auto simp add: quorem_def mod_def)
    done

    lemmas pos_mod_sign[simp]  = pos_mod_conj [THEN conjunct1, standard]
       and pos_mod_bound[simp] = pos_mod_conj [THEN conjunct2, standard]

    lemma neg_mod_conj : "b < (0::int) ==> a mod b ≤ 0 & b < a mod b"
    apply (cut_tac a = a and b = b in divAlg_correct)
    apply (auto simp add: quorem_def div_def mod_def)
    done

    lemmas neg_mod_sign[simp]  = neg_mod_conj [THEN conjunct1, standard]
       and neg_mod_bound[simp] = neg_mod_conj [THEN conjunct2, standard]

    subsection{*General Properties of div and mod*}

    lemma quorem_div_mod: "b ≠ 0 ==> quorem ((a, b), (a div b, a mod b))"
    apply (cut_tac a = a and b = b in zmod_zdiv_equality)
    apply (force simp add: quorem_def linorder_neq_iff)
    done

    lemma quorem_div: "[| quorem((a,b),(q,r));  b ≠ 0 |] ==> a div b = q"
    by (simp add: quorem_div_mod [THEN unique_quotient])

    lemma quorem_mod: "[| quorem((a,b),(q,r));  b ≠ 0 |] ==> a mod b = r"
    by (simp add: quorem_div_mod [THEN unique_remainder])

    lemma div_pos_pos_trivial: "[| (0::int) ≤ a;  a < b |] ==> a div b = 0"
    apply (rule quorem_div)
    apply (auto simp add: quorem_def)
    done

    lemma div_neg_neg_trivial: "[| a ≤ (0::int);  b < a |] ==> a div b = 0"
    apply (rule quorem_div)
    apply (auto simp add: quorem_def)
    done

    lemma div_pos_neg_trivial: "[| (0::int) < a;  a+b ≤ 0 |] ==> a div b = -1"
    apply (rule quorem_div)
    apply (auto simp add: quorem_def)
    done

    (*There is no div_neg_pos_trivial because  0 div b = 0 would supersede it*)

    lemma mod_pos_pos_trivial: "[| (0::int) ≤ a;  a < b |] ==> a mod b = a"
    apply (rule_tac q = 0 in quorem_mod)
    apply (auto simp add: quorem_def)
    done

    lemma mod_neg_neg_trivial: "[| a ≤ (0::int);  b < a |] ==> a mod b = a"
    apply (rule_tac q = 0 in quorem_mod)
    apply (auto simp add: quorem_def)
    done

    lemma mod_pos_neg_trivial: "[| (0::int) < a;  a+b ≤ 0 |] ==> a mod b = a+b"
    apply (rule_tac q = "-1" in quorem_mod)
    apply (auto simp add: quorem_def)
    done

    text{*There is no @{text mod_neg_pos_trivial}.*}

    (*Simpler laws such as -a div b = -(a div b) FAIL, but see just below*)
    lemma zdiv_zminus_zminus [simp]: "(-a) div (-b) = a div (b::int)"
    apply (case_tac "b = 0", simp)
    apply (simp add: quorem_div_mod [THEN quorem_neg, simplified,
                                     THEN quorem_div, THEN sym])

    done

    (*Simpler laws such as -a mod b = -(a mod b) FAIL, but see just below*)
    lemma zmod_zminus_zminus [simp]: "(-a) mod (-b) = - (a mod (b::int))"
    apply (case_tac "b = 0", simp)
    apply (subst quorem_div_mod [THEN quorem_neg, simplified, THEN quorem_mod],
           auto)
    done

    subsection{*Laws for div and mod with Unary Minus*}

    lemma zminus1_lemma:
         "quorem((a,b),(q,r))
          ==> quorem ((-a,b), (if r=0 then -q else -q - 1),
                              (if r=0 then 0 else b-r))"
    by (force simp add: split_ifs quorem_def linorder_neq_iff right_diff_distrib)

    lemma zdiv_zminus1_eq_if:
         "b ≠ (0::int)
          ==> (-a) div b =
              (if a mod b = 0 then - (a div b) else  - (a div b) - 1)"
    by (blast intro: quorem_div_mod [THEN zminus1_lemma, THEN quorem_div])

    lemma zmod_zminus1_eq_if:
         "(-a::int) mod b = (if a mod b = 0 then 0 else  b - (a mod b))"
    apply (case_tac "b = 0", simp)
    apply (blast intro: quorem_div_mod [THEN zminus1_lemma, THEN quorem_mod])
    done

    lemma zdiv_zminus2: "a div (-b) = (-a::int) div b"
    by (cut_tac a = "-a" in zdiv_zminus_zminus, auto)

    lemma zmod_zminus2: "a mod (-b) = - ((-a::int) mod b)"
    by (cut_tac a = "-a" and b = b in zmod_zminus_zminus, auto)

    lemma zdiv_zminus2_eq_if:
         "b ≠ (0::int)
          ==> a div (-b) =
              (if a mod b = 0 then - (a div b) else  - (a div b) - 1)"
    by (simp add: zdiv_zminus1_eq_if zdiv_zminus2)

    lemma zmod_zminus2_eq_if:
         "a mod (-b::int) = (if a mod b = 0 then 0 else  (a mod b) - b)"
    by (simp add: zmod_zminus1_eq_if zmod_zminus2)

    subsection{*Division of a Number by Itself*}

    lemma self_quotient_aux1: "[| (0::int) < a; a = r + a*q; r < a |] ==> 1 ≤ q"
    apply (subgoal_tac "0 < a*q")
     apply (simp add: zero_less_mult_iff, arith)
    done

    lemma self_quotient_aux2: "[| (0::int) < a; a = r + a*q; 0 ≤ r |] ==> q ≤ 1"
    apply (subgoal_tac "0 ≤ a* (1-q) ")
     apply (simp add: zero_le_mult_iff)
    apply (simp add: right_diff_distrib)
    done

    lemma self_quotient: "[| quorem((a,a),(q,r));  a ≠ (0::int) |] ==> q = 1"
    apply (simp add: split_ifs quorem_def linorder_neq_iff)
    apply (rule order_antisym, safe, simp_all)
    apply (rule_tac [3] a = "-a" and r = "-r" in self_quotient_aux1)
    apply (rule_tac a = "-a" and r = "-r" in self_quotient_aux2)
    apply (force intro: self_quotient_aux1 self_quotient_aux2 simp add: add_commute)+
    done

    lemma self_remainder: "[| quorem((a,a),(q,r));  a ≠ (0::int) |] ==> r = 0"
    apply (frule self_quotient, assumption)
    apply (simp add: quorem_def)
    done

    lemma zdiv_self [simp]: "a ≠ 0 ==> a div a = (1::int)"
    by (simp add: quorem_div_mod [THEN self_quotient])

    (*Here we have 0 mod 0 = 0, also assumed by Knuth (who puts m mod 0 = 0) *)
    lemma zmod_self [simp]: "a mod a = (0::int)"
    apply (case_tac "a = 0", simp)
    apply (simp add: quorem_div_mod [THEN self_remainder])
    done

    subsection{*Computation of Division and Remainder*}

    lemma zdiv_zero [simp]: "(0::int) div b = 0"
    by (simp add: div_def divAlg_def)

    lemma div_eq_minus1: "(0::int) < b ==> -1 div b = -1"
    by (simp add: div_def divAlg_def)

    lemma zmod_zero [simp]: "(0::int) mod b = 0"
    by (simp add: mod_def divAlg_def)

    lemma zdiv_minus1: "(0::int) < b ==> -1 div b = -1"
    by (simp add: div_def divAlg_def)

    lemma zmod_minus1: "(0::int) < b ==> -1 mod b = b - 1"
    by (simp add: mod_def divAlg_def)

    text{*a positive, b positive *}

    lemma div_pos_pos: "[| 0 < a;  0 ≤ b |] ==> a div b = fst (posDivAlg(a,b))"
    by (simp add: div_def divAlg_def)

    lemma mod_pos_pos: "[| 0 < a;  0 ≤ b |] ==> a mod b = snd (posDivAlg(a,b))"
    by (simp add: mod_def divAlg_def)

    text{*a negative, b positive *}

    lemma div_neg_pos: "[| a < 0;  0 < b |] ==> a div b = fst (negDivAlg(a,b))"
    by (simp add: div_def divAlg_def)

    lemma mod_neg_pos: "[| a < 0;  0 < b |] ==> a mod b = snd (negDivAlg(a,b))"
    by (simp add: mod_def divAlg_def)

    text{*a positive, b negative *}

    lemma div_pos_neg:
         "[| 0 < a;  b < 0 |] ==> a div b = fst (negateSnd(negDivAlg(-a,-b)))"
    by (simp add: div_def divAlg_def)

    lemma mod_pos_neg:
         "[| 0 < a;  b < 0 |] ==> a mod b = snd (negateSnd(negDivAlg(-a,-b)))"
    by (simp add: mod_def divAlg_def)

    text{*a negative, b negative *}

    lemma div_neg_neg:
         "[| a < 0;  b ≤ 0 |] ==> a div b = fst (negateSnd(posDivAlg(-a,-b)))"
    by (simp add: div_def divAlg_def)

    lemma mod_neg_neg:
         "[| a < 0;  b ≤ 0 |] ==> a mod b = snd (negateSnd(posDivAlg(-a,-b)))"
    by (simp add: mod_def divAlg_def)

    text {*Simplify expresions in which div and mod combine numerical constants*}

    lemmas div_pos_pos_number_of =
        div_pos_pos [of "number_of v" "number_of w", standard]
    declare div_pos_pos_number_of [simp]

    lemmas div_neg_pos_number_of =
        div_neg_pos [of "number_of v" "number_of w", standard]
    declare div_neg_pos_number_of [simp]

    lemmas div_pos_neg_number_of =
        div_pos_neg [of "number_of v" "number_of w", standard]
    declare div_pos_neg_number_of [simp]

    lemmas div_neg_neg_number_of =
        div_neg_neg [of "number_of v" "number_of w", standard]
    declare div_neg_neg_number_of [simp]

    lemmas mod_pos_pos_number_of =
        mod_pos_pos [of "number_of v" "number_of w", standard]
    declare mod_pos_pos_number_of [simp]

    lemmas mod_neg_pos_number_of =
        mod_neg_pos [of "number_of v" "number_of w", standard]
    declare mod_neg_pos_number_of [simp]

    lemmas mod_pos_neg_number_of =
        mod_pos_neg [of "number_of v" "number_of w", standard]
    declare mod_pos_neg_number_of [simp]

    lemmas mod_neg_neg_number_of =
        mod_neg_neg [of "number_of v" "number_of w", standard]
    declare mod_neg_neg_number_of [simp]

    lemmas posDivAlg_eqn_number_of =
        posDivAlg_eqn [of "number_of v" "number_of w", standard]
    declare posDivAlg_eqn_number_of [simp]

    lemmas negDivAlg_eqn_number_of =
        negDivAlg_eqn [of "number_of v" "number_of w", standard]
    declare negDivAlg_eqn_number_of [simp]

    text{*Special-case simplification *}

    lemma zmod_1 [simp]: "a mod (1::int) = 0"
    apply (cut_tac a = a and b = 1 in pos_mod_sign)
    apply (cut_tac [2] a = a and b = 1 in pos_mod_bound)
    apply (auto simp del:pos_mod_bound pos_mod_sign)
    done

    lemma zdiv_1 [simp]: "a div (1::int) = a"
    by (cut_tac a = a and b = 1 in zmod_zdiv_equality, auto)

    lemma zmod_minus1_right [simp]: "a mod (-1::int) = 0"
    apply (cut_tac a = a and b = "-1" in neg_mod_sign)
    apply (cut_tac [2] a = a and b = "-1" in neg_mod_bound)
    apply (auto simp del: neg_mod_sign neg_mod_bound)
    done

    lemma zdiv_minus1_right [simp]: "a div (-1::int) = -a"
    by (cut_tac a = a and b = "-1" in zmod_zdiv_equality, auto)

    (** The last remaining special cases for constant arithmetic:
        1 div z and 1 mod z **)

    lemmas div_pos_pos_1_number_of =
        div_pos_pos [OF int_0_less_1, of "number_of w", standard]
    declare div_pos_pos_1_number_of [simp]

    lemmas div_pos_neg_1_number_of =
        div_pos_neg [OF int_0_less_1, of "number_of w", standard]
    declare div_pos_neg_1_number_of [simp]

    lemmas mod_pos_pos_1_number_of =
        mod_pos_pos [OF int_0_less_1, of "number_of w", standard]
    declare mod_pos_pos_1_number_of [simp]

    lemmas mod_pos_neg_1_number_of =
        mod_pos_neg [OF int_0_less_1, of "number_of w", standard]
    declare mod_pos_neg_1_number_of [simp]

    lemmas posDivAlg_eqn_1_number_of =
        posDivAlg_eqn [of concl: 1 "number_of w", standard]
    declare posDivAlg_eqn_1_number_of [simp]

    lemmas negDivAlg_eqn_1_number_of =
        negDivAlg_eqn [of concl: 1 "number_of w", standard]
    declare negDivAlg_eqn_1_number_of [simp]

    subsection{*Monotonicity in the First Argument (Dividend)*}

    lemma zdiv_mono1: "[| a ≤ a';  0 < (b::int) |] ==> a div b ≤ a' div b"
    apply (cut_tac a = a and b = b in zmod_zdiv_equality)
    apply (cut_tac a = a' and b = b in zmod_zdiv_equality)
    apply (rule unique_quotient_lemma)
    apply (erule subst)
    apply (erule subst, simp_all)
    done

    lemma zdiv_mono1_neg: "[| a ≤ a';  (b::int) < 0 |] ==> a' div b ≤ a div b"
    apply (cut_tac a = a and b = b in zmod_zdiv_equality)
    apply (cut_tac a = a' and b = b in zmod_zdiv_equality)
    apply (rule unique_quotient_lemma_neg)
    apply (erule subst)
    apply (erule subst, simp_all)
    done

    subsection{*Monotonicity in the Second Argument (Divisor)*}

    lemma q_pos_lemma:
         "[| 0 ≤ b'*q' + r'; r' < b';  0 < b' |] ==> 0 ≤ (q'::int)"
    apply (subgoal_tac "0 < b'* (q' + 1) ")
     apply (simp add: zero_less_mult_iff)
    apply (simp add: right_distrib)
    done

    lemma zdiv_mono2_lemma:
         "[| b*q + r = b'*q' + r';  0 ≤ b'*q' + r';
             r' < b';  0 ≤ r;  0 < b';  b' ≤ b |]
          ==> q ≤ (q'::int)"
    apply (frule q_pos_lemma, assumption+)
    apply (subgoal_tac "b*q < b* (q' + 1) ")
     apply (simp add: mult_less_cancel_left)
    apply (subgoal_tac "b*q = r' - r + b'*q'")
     prefer 2 apply simp
    apply (simp (no_asm_simp) add: right_distrib)
    apply (subst add_commute, rule zadd_zless_mono, arith)
    apply (rule mult_right_mono, auto)
    done

    lemma zdiv_mono2:
         "[| (0::int) ≤ a;  0 < b';  b' ≤ b |] ==> a div b ≤ a div b'"
    apply (subgoal_tac "b ≠ 0")
     prefer 2 apply arith
    apply (cut_tac a = a and b = b in zmod_zdiv_equality)
    apply (cut_tac a = a and b = b' in zmod_zdiv_equality)
    apply (rule zdiv_mono2_lemma)
    apply (erule subst)
    apply (erule subst, simp_all)
    done

    lemma q_neg_lemma:
         "[| b'*q' + r' < 0;  0 ≤ r';  0 < b' |] ==> q' ≤ (0::int)"
    apply (subgoal_tac "b'*q' < 0")
     apply (simp add: mult_less_0_iff, arith)
    done

    lemma zdiv_mono2_neg_lemma:
         "[| b*q + r = b'*q' + r';  b'*q' + r' < 0;
             r < b;  0 ≤ r';  0 < b';  b' ≤ b |]
          ==> q' ≤ (q::int)"
    apply (frule q_neg_lemma, assumption+)
    apply (subgoal_tac "b*q' < b* (q + 1) ")
     apply (simp add: mult_less_cancel_left)
    apply (simp add: right_distrib)
    apply (subgoal_tac "b*q' ≤ b'*q'")
     prefer 2 apply (simp add: mult_right_mono_neg, arith)
    done

    lemma zdiv_mono2_neg:
         "[| a < (0::int);  0 < b';  b' ≤ b |] ==> a div b' ≤ a div b"
    apply (cut_tac a = a and b = b in zmod_zdiv_equality)
    apply (cut_tac a = a and b = b' in zmod_zdiv_equality)
    apply (rule zdiv_mono2_neg_lemma)
    apply (erule subst)
    apply (erule subst, simp_all)
    done

    subsection{*More Algebraic Laws for div and mod*}

    text{*proving (a*b) div c = a * (b div c) + a * (b mod c) *}

    lemma zmult1_lemma:
         "[| quorem((b,c),(q,r));  c ≠ 0 |]
          ==> quorem ((a*b, c), (a*q + a*r div c, a*r mod c))"
    by (force simp add: split_ifs quorem_def linorder_neq_iff right_distrib)

    lemma zdiv_zmult1_eq: "(a*b) div c = a*(b div c) + a*(b mod c) div (c::int)"
    apply (case_tac "c = 0", simp)
    apply (blast intro: quorem_div_mod [THEN zmult1_lemma, THEN quorem_div])
    done

    lemma zmod_zmult1_eq: "(a*b) mod c = a*(b mod c) mod (c::int)"
    apply (case_tac "c = 0", simp)
    apply (blast intro: quorem_div_mod [THEN zmult1_lemma, THEN quorem_mod])
    done

    lemma zmod_zmult1_eq': "(a*b) mod (c::int) = ((a mod c) * b) mod c"
    apply (rule trans)
    apply (rule_tac s = "b*a mod c" in trans)
    apply (rule_tac [2] zmod_zmult1_eq)
    apply (simp_all add: mult_commute)
    done

    lemma zmod_zmult_distrib: "(a*b) mod (c::int) = ((a mod c) * (b mod c)) mod c"
    apply (rule zmod_zmult1_eq' [THEN trans])
    apply (rule zmod_zmult1_eq)
    done

    lemma zdiv_zmult_self1 [simp]: "b ≠ (0::int) ==> (a*b) div b = a"
    by (simp add: zdiv_zmult1_eq)

    lemma zdiv_zmult_self2 [simp]: "b ≠ (0::int) ==> (b*a) div b = a"
    by (subst mult_commute, erule zdiv_zmult_self1)

    lemma zmod_zmult_self1 [simp]: "(a*b) mod b = (0::int)"
    by (simp add: zmod_zmult1_eq)

    lemma zmod_zmult_self2 [simp]: "(b*a) mod b = (0::int)"
    by (simp add: mult_commute zmod_zmult1_eq)

    lemma zmod_eq_0_iff: "(m mod d = 0) = (EX q::int. m = d*q)"
    proof
      assume "m mod d = 0"
      with zmod_zdiv_equality[of m d] show "EX q::int. m = d*q" by auto
    next
      assume "EX q::int. m = d*q"
      thus "m mod d = 0" by auto
    qed

    lemmas zmod_eq_0D = zmod_eq_0_iff [THEN iffD1]
    declare zmod_eq_0D [dest!]

    text{*proving (a+b) div c = a div c + b div c + ((a mod c + b mod c) div c) *}

    lemma zadd1_lemma:
         "[| quorem((a,c),(aq,ar));  quorem((b,c),(bq,br));  c ≠ 0 |]
          ==> quorem ((a+b, c), (aq + bq + (ar+br) div c, (ar+br) mod c))"
    by (force simp add: split_ifs quorem_def linorder_neq_iff right_distrib)

    (*NOT suitable for rewriting: the RHS has an instance of the LHS*)
    lemma zdiv_zadd1_eq:
         "(a+b) div (c::int) = a div c + b div c + ((a mod c + b mod c) div c)"
    apply (case_tac "c = 0", simp)
    apply (blast intro: zadd1_lemma [OF quorem_div_mod quorem_div_mod] quorem_div)
    done

    lemma zmod_zadd1_eq: "(a+b) mod (c::int) = (a mod c + b mod c) mod c"
    apply (case_tac "c = 0", simp)
    apply (blast intro: zadd1_lemma [OF quorem_div_mod quorem_div_mod] quorem_mod)
    done

    lemma mod_div_trivial [simp]: "(a mod b) div b = (0::int)"
    apply (case_tac "b = 0", simp)
    apply (auto simp add: linorder_neq_iff div_pos_pos_trivial div_neg_neg_trivial)
    done

    lemma mod_mod_trivial [simp]: "(a mod b) mod b = a mod (b::int)"
    apply (case_tac "b = 0", simp)
    apply (force simp add: linorder_neq_iff mod_pos_pos_trivial mod_neg_neg_trivial)
    done

    lemma zmod_zadd_left_eq: "(a+b) mod (c::int) = ((a mod c) + b) mod c"
    apply (rule trans [symmetric])
    apply (rule zmod_zadd1_eq, simp)
    apply (rule zmod_zadd1_eq [symmetric])
    done

    lemma zmod_zadd_right_eq: "(a+b) mod (c::int) = (a + (b mod c)) mod c"
    apply (rule trans [symmetric])
    apply (rule zmod_zadd1_eq, simp)
    apply (rule zmod_zadd1_eq [symmetric])
    done

    lemma zdiv_zadd_self1[simp]: "a ≠ (0::int) ==> (a+b) div a = b div a + 1"
    by (simp add: zdiv_zadd1_eq)

    lemma zdiv_zadd_self2[simp]: "a ≠ (0::int) ==> (b+a) div a = b div a + 1"
    by (simp add: zdiv_zadd1_eq)

    lemma zmod_zadd_self1[simp]: "(a+b) mod a = b mod (a::int)"
    apply (case_tac "a = 0", simp)
    apply (simp add: zmod_zadd1_eq)
    done

    lemma zmod_zadd_self2[simp]: "(b+a) mod a = b mod (a::int)"
    apply (case_tac "a = 0", simp)
    apply (simp add: zmod_zadd1_eq)
    done

    subsection{*Proving  @{term "a div (b*c) = (a div b) div c"} *}

    (*The condition c>0 seems necessary.  Consider that 7 div ~6 = ~2 but
      7 div 2 div ~3 = 3 div ~3 = ~1.  The subcase (a div b) mod c = 0 seems
      to cause particular problems.*)

    text{*first, four lemmas to bound the remainder for the cases b<0 and b>0 *}

    lemma zmult2_lemma_aux1: "[| (0::int) < c;  b < r;  r ≤ 0 |] ==> b*c < b*(q mod c) + r"
    apply (subgoal_tac "b * (c - q mod c) < r * 1")
    apply (simp add: right_diff_distrib)
    apply (rule order_le_less_trans)
    apply (erule_tac [2] mult_strict_right_mono)
    apply (rule mult_left_mono_neg)
    apply (auto simp add: compare_rls add_commute [of 1]
                          add1_zle_eq pos_mod_bound)
    done

    lemma zmult2_lemma_aux2:
         "[| (0::int) < c;   b < r;  r ≤ 0 |] ==> b * (q mod c) + r ≤ 0"
    apply (subgoal_tac "b * (q mod c) ≤ 0")
     apply arith
    apply (simp add: mult_le_0_iff)
    done

    lemma zmult2_lemma_aux3: "[| (0::int) < c;  0 ≤ r;  r < b |] ==> 0 ≤ b * (q mod c) + r"
    apply (subgoal_tac "0 ≤ b * (q mod c) ")
    apply arith
    apply (simp add: zero_le_mult_iff)
    done

    lemma zmult2_lemma_aux4: "[| (0::int) < c; 0 ≤ r; r < b |] ==> b * (q mod c) + r < b * c"
    apply (subgoal_tac "r * 1 < b * (c - q mod c) ")
    apply (simp add: right_diff_distrib)
    apply (rule order_less_le_trans)
    apply (erule mult_strict_right_mono)
    apply (rule_tac [2] mult_left_mono)
    apply (auto simp add: compare_rls add_commute [of 1]
                          add1_zle_eq pos_mod_bound)
    done

    lemma zmult2_lemma: "[| quorem ((a,b), (q,r));  b ≠ 0;  0 < c |]
          ==> quorem ((a, b*c), (q div c, b*(q mod c) + r))"
    by (auto simp add: mult_ac quorem_def linorder_neq_iff
                       zero_less_mult_iff right_distrib [symmetric]
                       zmult2_lemma_aux1 zmult2_lemma_aux2 zmult2_lemma_aux3 zmult2_lemma_aux4)

    lemma zdiv_zmult2_eq: "(0::int) < c ==> a div (b*c) = (a div b) div c"
    apply (case_tac "b = 0", simp)
    apply (force simp add: quorem_div_mod [THEN zmult2_lemma, THEN quorem_div])
    done

    lemma zmod_zmult2_eq:
         "(0::int) < c ==> a mod (b*c) = b*(a div b mod c) + a mod b"
    apply (case_tac "b = 0", simp)
    apply (force simp add: quorem_div_mod [THEN zmult2_lemma, THEN quorem_mod])
    done

    subsection{*Cancellation of Common Factors in div*}

    lemma zdiv_zmult_zmult1_aux1:
         "[| (0::int) < b;  c ≠ 0 |] ==> (c*a) div (c*b) = a div b"
    by (subst zdiv_zmult2_eq, auto)

    lemma zdiv_zmult_zmult1_aux2:
         "[| b < (0::int);  c ≠ 0 |] ==> (c*a) div (c*b) = a div b"
    apply (subgoal_tac " (c * (-a)) div (c * (-b)) = (-a) div (-b) ")
    apply (rule_tac [2] zdiv_zmult_zmult1_aux1, auto)
    done

    lemma zdiv_zmult_zmult1: "c ≠ (0::int) ==> (c*a) div (c*b) = a div b"
    apply (case_tac "b = 0", simp)
    apply (auto simp add: linorder_neq_iff zdiv_zmult_zmult1_aux1 zdiv_zmult_zmult1_aux2)
    done

    lemma zdiv_zmult_zmult2: "c ≠ (0::int) ==> (a*c) div (b*c) = a div b"
    apply (drule zdiv_zmult_zmult1)
    apply (auto simp add: mult_commute)
    done

    subsection{*Distribution of Factors over mod*}

    lemma zmod_zmult_zmult1_aux1:
         "[| (0::int) < b;  c ≠ 0 |] ==> (c*a) mod (c*b) = c * (a mod b)"
    by (subst zmod_zmult2_eq, auto)

    lemma zmod_zmult_zmult1_aux2:
         "[| b < (0::int);  c ≠ 0 |] ==> (c*a) mod (c*b) = c * (a mod b)"
    apply (subgoal_tac " (c * (-a)) mod (c * (-b)) = c * ((-a) mod (-b))")
    apply (rule_tac [2] zmod_zmult_zmult1_aux1, auto)
    done

    lemma zmod_zmult_zmult1: "(c*a) mod (c*b) = (c::int) * (a mod b)"
    apply (case_tac "b = 0", simp)
    apply (case_tac "c = 0", simp)
    apply (auto simp add: linorder_neq_iff zmod_zmult_zmult1_aux1 zmod_zmult_zmult1_aux2)
    done

    lemma zmod_zmult_zmult2: "(a*c) mod (b*c) = (a mod b) * (c::int)"
    apply (cut_tac c = c in zmod_zmult_zmult1)
    apply (auto simp add: mult_commute)
    done

    subsection {*Splitting Rules for div and mod*}

    text{*The proofs of the two lemmas below are essentially identical*}

    lemma split_pos_lemma:
     "0<k ==>
        P(n div k :: int)(n mod k) = (∀i j. 0≤j & j<k & n = k*i + j --> P i j)"
    apply (rule iffI, clarify)
     apply (erule_tac P="P ?x ?y" in rev_mp)
     apply (subst zmod_zadd1_eq)
     apply (subst zdiv_zadd1_eq)
     apply (simp add: div_pos_pos_trivial mod_pos_pos_trivial)
    txt{*converse direction*}
    apply (drule_tac x = "n div k" in spec)
    apply (drule_tac x = "n mod k" in spec, simp)
    done

    lemma split_neg_lemma:
     "k<0 ==>
        P(n div k :: int)(n mod k) = (∀i j. k<j & j≤0 & n = k*i + j --> P i j)"
    apply (rule iffI, clarify)
     apply (erule_tac P="P ?x ?y" in rev_mp)
     apply (subst zmod_zadd1_eq)
     apply (subst zdiv_zadd1_eq)
     apply (simp add: div_neg_neg_trivial mod_neg_neg_trivial)
    txt{*converse direction*}
    apply (drule_tac x = "n div k" in spec)
    apply (drule_tac x = "n mod k" in spec, simp)
    done

    lemma split_zdiv:
     "P(n div k :: int) =
      ((k = 0 --> P 0) &
       (0<k --> (∀i j. 0≤j & j<k & n = k*i + j --> P i)) &
       (k<0 --> (∀i j. k<j & j≤0 & n = k*i + j --> P i)))"
    apply (case_tac "k=0", simp)
    apply (simp only: linorder_neq_iff)
    apply (erule disjE)
     apply (simp_all add: split_pos_lemma [of concl: "%x y. P x"]
                          split_neg_lemma [of concl: "%x y. P x"])
    done

    lemma split_zmod:
     "P(n mod k :: int) =
      ((k = 0 --> P n) &
       (0<k --> (∀i j. 0≤j & j<k & n = k*i + j --> P j)) &
       (k<0 --> (∀i j. k<j & j≤0 & n = k*i + j --> P j)))"
    apply (case_tac "k=0", simp)
    apply (simp only: linorder_neq_iff)
    apply (erule disjE)
     apply (simp_all add: split_pos_lemma [of concl: "%x y. P y"]
                          split_neg_lemma [of concl: "%x y. P y"])
    done

    (* Enable arith to deal with div 2 and mod 2: *)
    declare split_zdiv [of _ _ "number_of k", simplified, standard, arith_split]
    declare split_zmod [of _ _ "number_of k", simplified, standard, arith_split]

    subsection{*Speeding up the Division Algorithm with Shifting*}

    text{*computing div by shifting *}

    lemma pos_zdiv_mult_2: "(0::int) ≤ a ==> (1 + 2*b) div (2*a) = b div a"
    proof cases
      assume "a=0"
        thus ?thesis by simp
    next
      assume "a≠0" and le_a: "0≤a"
      hence a_pos: "1 ≤ a" by arith
      hence one_less_a2: "1 < 2*a" by arith
      hence le_2a: "2 * (1 + b mod a) ≤ 2 * a"
        by (simp add: mult_le_cancel_left add_commute [of 1] add1_zle_eq)
      with a_pos have "0 ≤ b mod a" by simp
      hence le_addm: "0 ≤ 1 mod (2*a) + 2*(b mod a)"
        by (simp add: mod_pos_pos_trivial one_less_a2)
      with  le_2a
      have "(1 mod (2*a) + 2*(b mod a)) div (2*a) = 0"
        by (simp add: div_pos_pos_trivial le_addm mod_pos_pos_trivial one_less_a2
                      right_distrib)
      thus ?thesis
        by (subst zdiv_zadd1_eq,
            simp add: zdiv_zmult_zmult1 zmod_zmult_zmult1 one_less_a2
                      div_pos_pos_trivial)
    qed

    lemma neg_zdiv_mult_2: "a ≤ (0::int) ==> (1 + 2*b) div (2*a) = (b+1) div a"
    apply (subgoal_tac " (1 + 2* (-b - 1)) div (2 * (-a)) = (-b - 1) div (-a) ")
    apply (rule_tac [2] pos_zdiv_mult_2)
    apply (auto simp add: minus_mult_right [symmetric] right_diff_distrib)
    apply (subgoal_tac " (-1 - (2 * b)) = - (1 + (2 * b))")
    apply (simp only: zdiv_zminus_zminus diff_minus minus_add_distrib [symmetric],
           simp)
    done

    (*Not clear why this must be proved separately; probably number_of causes
      simplification problems*)
    lemma not_0_le_lemma: "~ 0 ≤ x ==> x ≤ (0::int)"
    by auto

    lemma zdiv_number_of_BIT[simp]:
         "number_of (v BIT b) div number_of (w BIT bit.B0) =
              (if b=bit.B0 | (0::int) ≤ number_of w
               then number_of v div (number_of w)
               else (number_of v + (1::int)) div (number_of w))"
    apply (simp only: number_of_eq Bin_simps UNIV_I split: split_if)
    apply (simp add: zdiv_zmult_zmult1 pos_zdiv_mult_2 neg_zdiv_mult_2 add_ac
                split: bit.split)
    done

    subsection{*Computing mod by Shifting (proofs resemble those for div)*}

    lemma pos_zmod_mult_2:
         "(0::int) ≤ a ==> (1 + 2*b) mod (2*a) = 1 + 2 * (b mod a)"
    apply (case_tac "a = 0", simp)
    apply (subgoal_tac "1 < a * 2")
     prefer 2 apply arith
    apply (subgoal_tac "2* (1 + b mod a) ≤ 2*a")
     apply (rule_tac [2] mult_left_mono)
    apply (auto simp add: add_commute [of 1] mult_commute add1_zle_eq
                          pos_mod_bound)
    apply (subst zmod_zadd1_eq)
    apply (simp add: zmod_zmult_zmult2 mod_pos_pos_trivial)
    apply (rule mod_pos_pos_trivial)
    apply (auto simp add: mod_pos_pos_trivial left_distrib)
    apply (subgoal_tac "0 ≤ b mod a", arith, simp)
    done

    lemma neg_zmod_mult_2:
         "a ≤ (0::int) ==> (1 + 2*b) mod (2*a) = 2 * ((b+1) mod a) - 1"
    apply (subgoal_tac "(1 + 2* (-b - 1)) mod (2* (-a)) =
                        1 + 2* ((-b - 1) mod (-a))")
    apply (rule_tac [2] pos_zmod_mult_2)
    apply (auto simp add: minus_mult_right [symmetric] right_diff_distrib)
    apply (subgoal_tac " (-1 - (2 * b)) = - (1 + (2 * b))")
     prefer 2 apply simp
    apply (simp only: zmod_zminus_zminus diff_minus minus_add_distrib [symmetric])
    done

    lemma zmod_number_of_BIT [simp]:
         "number_of (v BIT b) mod number_of (w BIT bit.B0) =
          (case b of
              bit.B0 => 2 * (number_of v mod number_of w)
            | bit.B1 => if (0::int) ≤ number_of w
                    then 2 * (number_of v mod number_of w) + 1
                    else 2 * ((number_of v + (1::int)) mod number_of w) - 1)"
    apply (simp only: number_of_eq Bin_simps UNIV_I split: bit.split)
    apply (simp add: zmod_zmult_zmult1 pos_zmod_mult_2
                     not_0_le_lemma neg_zmod_mult_2 add_ac)
    done

    subsection{*Quotients of Signs*}

    lemma div_neg_pos_less0: "[| a < (0::int);  0 < b |] ==> a div b < 0"
    apply (subgoal_tac "a div b ≤ -1", force)
    apply (rule order_trans)
    apply (rule_tac a' = "-1" in zdiv_mono1)
    apply (auto simp add: zdiv_minus1)
    done

    lemma div_nonneg_neg_le0: "[| (0::int) ≤ a;  b < 0 |] ==> a div b ≤ 0"
    by (drule zdiv_mono1_neg, auto)

    lemma pos_imp_zdiv_nonneg_iff: "(0::int) < b ==> (0 ≤ a div b) = (0 ≤ a)"
    apply auto
    apply (drule_tac [2] zdiv_mono1)
    apply (auto simp add: linorder_neq_iff)
    apply (simp (no_asm_use) add: linorder_not_less [symmetric])
    apply (blast intro: div_neg_pos_less0)
    done

    lemma neg_imp_zdiv_nonneg_iff:
         "b < (0::int) ==> (0 ≤ a div b) = (a ≤ (0::int))"
    apply (subst zdiv_zminus_zminus [symmetric])
    apply (subst pos_imp_zdiv_nonneg_iff, auto)
    done

    (*But not (a div b ≤ 0 iff a≤0); consider a=1, b=2 when a div b = 0.*)
    lemma pos_imp_zdiv_neg_iff: "(0::int) < b ==> (a div b < 0) = (a < 0)"
    by (simp add: linorder_not_le [symmetric] pos_imp_zdiv_nonneg_iff)

    (*Again the law fails for ≤: consider a = -1, b = -2 when a div b = 0*)
    lemma neg_imp_zdiv_neg_iff: "b < (0::int) ==> (a div b < 0) = (0 < a)"
    by (simp add: linorder_not_le [symmetric] neg_imp_zdiv_nonneg_iff)

    subsection {* The Divides Relation *}

    lemma zdvd_iff_zmod_eq_0: "(m dvd n) = (n mod m = (0::int))"
    by(simp add:dvd_def zmod_eq_0_iff)

    lemma zdvd_0_right [iff]: "(m::int) dvd 0"
    by (simp add: dvd_def)

    lemma zdvd_0_left [iff]: "(0 dvd (m::int)) = (m = 0)"
      by (simp add: dvd_def)

    lemma zdvd_1_left [iff]: "1 dvd (m::int)"
      by (simp add: dvd_def)

    lemma zdvd_refl [simp]: "m dvd (m::int)"
    by (auto simp add: dvd_def intro: zmult_1_right [symmetric])

    lemma zdvd_trans: "m dvd n ==> n dvd k ==> m dvd (k::int)"
    by (auto simp add: dvd_def intro: mult_assoc)

    lemma zdvd_zminus_iff: "(m dvd -n) = (m dvd (n::int))"
      apply (simp add: dvd_def, auto)
       apply (rule_tac [!] x = "-k" in exI, auto)
      done

    lemma zdvd_zminus2_iff: "(-m dvd n) = (m dvd (n::int))"
      apply (simp add: dvd_def, auto)
       apply (rule_tac [!] x = "-k" in exI, auto)
      done

    lemma zdvd_anti_sym:
        "0 < m ==> 0 < n ==> m dvd n ==> n dvd m ==> m = (n::int)"
      apply (simp add: dvd_def, auto)
      apply (simp add: mult_assoc zero_less_mult_iff zmult_eq_1_iff)
      done

    lemma zdvd_zadd: "k dvd m ==> k dvd n ==> k dvd (m + n :: int)"
      apply (simp add: dvd_def)
      apply (blast intro: right_distrib [symmetric])
      done

    lemma zdvd_zdiff: "k dvd m ==> k dvd n ==> k dvd (m - n :: int)"
      apply (simp add: dvd_def)
      apply (blast intro: right_diff_distrib [symmetric])
      done

    lemma zdvd_zdiffD: "k dvd m - n ==> k dvd n ==> k dvd (m::int)"
      apply (subgoal_tac "m = n + (m - n)")
       apply (erule ssubst)
       apply (blast intro: zdvd_zadd, simp)
      done

    lemma zdvd_zmult: "k dvd (n::int) ==> k dvd m * n"
      apply (simp add: dvd_def)
      apply (blast intro: mult_left_commute)
      done

    lemma zdvd_zmult2: "k dvd (m::int) ==> k dvd m * n"
      apply (subst mult_commute)
      apply (erule zdvd_zmult)
      done

    lemma zdvd_triv_right [iff]: "(k::int) dvd m * k"
      apply (rule zdvd_zmult)
      apply (rule zdvd_refl)
      done

    lemma zdvd_triv_left [iff]: "(k::int) dvd k * m"
      apply (rule zdvd_zmult2)
      apply (rule zdvd_refl)
      done

    lemma zdvd_zmultD2: "j * k dvd n ==> j dvd (n::int)"
      apply (simp add: dvd_def)
      apply (simp add: mult_assoc, blast)
      done

    lemma zdvd_zmultD: "j * k dvd n ==> k dvd (n::int)"
      apply (rule zdvd_zmultD2)
      apply (subst mult_commute, assumption)
      done

    lemma zdvd_zmult_mono: "i dvd m ==> j dvd (n::int) ==> i * j dvd m * n"
      apply (simp add: dvd_def, clarify)
      apply (rule_tac x = "k * ka" in exI)
      apply (simp add: mult_ac)
      done

    lemma zdvd_reduce: "(k dvd n + k * m) = (k dvd (n::int))"
      apply (rule iffI)
       apply (erule_tac [2] zdvd_zadd)
       apply (subgoal_tac "n = (n + k * m) - k * m")
        apply (erule ssubst)
        apply (erule zdvd_zdiff, simp_all)
      done

    lemma zdvd_zmod: "f dvd m ==> f dvd (n::int) ==> f dvd m mod n"
      apply (simp add: dvd_def)
      apply (auto simp add: zmod_zmult_zmult1)
      done

    lemma zdvd_zmod_imp_zdvd: "k dvd m mod n ==> k dvd n ==> k dvd (m::int)"
      apply (subgoal_tac "k dvd n * (m div n) + m mod n")
       apply (simp add: zmod_zdiv_equality [symmetric])
      apply (simp only: zdvd_zadd zdvd_zmult2)
      done

    lemma zdvd_not_zless: "0 < m ==> m < n ==> ¬ n dvd (m::int)"
      apply (simp add: dvd_def, auto)
      apply (subgoal_tac "0 < n")
       prefer 2
       apply (blast intro: order_less_trans)
      apply (simp add: zero_less_mult_iff)
      apply (subgoal_tac "n * k < n * 1")
       apply (drule mult_less_cancel_left [THEN iffD1], auto)
      done

    lemma int_dvd_iff: "(int m dvd z) = (m dvd nat (abs z))"
      apply (auto simp add: dvd_def nat_abs_mult_distrib)
      apply (auto simp add: nat_eq_iff abs_if split add: split_if_asm)
       apply (rule_tac x = "-(int k)" in exI)
      apply (auto simp add: int_mult)
      done

    lemma dvd_int_iff: "(z dvd int m) = (nat (abs z) dvd m)"
      apply (auto simp add: dvd_def abs_if int_mult)
        apply (rule_tac [3] x = "nat k" in exI)
        apply (rule_tac [2] x = "-(int k)" in exI)
        apply (rule_tac x = "nat (-k)" in exI)
        apply (cut_tac [3] k = m in int_less_0_conv)
        apply (cut_tac k = m in int_less_0_conv)
        apply (auto simp add: zero_le_mult_iff mult_less_0_iff
          nat_mult_distrib [symmetric] nat_eq_iff2)
      done

    lemma nat_dvd_iff: "(nat z dvd m) = (if 0 ≤ z then (z dvd int m) else m = 0)"
      apply (auto simp add: dvd_def int_mult)
      apply (rule_tac x = "nat k" in exI)
      apply (cut_tac k = m in int_less_0_conv)
      apply (auto simp add: zero_le_mult_iff mult_less_0_iff
        nat_mult_distrib [symmetric] nat_eq_iff2)
      done

    lemma zminus_dvd_iff [iff]: "(-z dvd w) = (z dvd (w::int))"
      apply (auto simp add: dvd_def)
       apply (rule_tac [!] x = "-k" in exI, auto)
      done

    lemma dvd_zminus_iff [iff]: "(z dvd -w) = (z dvd (w::int))"
      apply (auto simp add: dvd_def)
       apply (drule minus_equation_iff [THEN iffD1])
       apply (rule_tac [!] x = "-k" in exI, auto)
      done

    lemma zdvd_imp_le: "[| z dvd n; 0 < n |] ==> z ≤ (n::int)"
      apply (rule_tac z=n in int_cases)
      apply (auto simp add: dvd_int_iff)
      apply (rule_tac z=z in int_cases)
      apply (auto simp add: dvd_imp_le)
      done

    subsection{*Integer Powers*}

    instance int :: power ..

    primrec
      "p ^ 0 = 1"
      "p ^ (Suc n) = (p::int) * (p ^ n)"

    instance int :: recpower
    proof
      fix z :: int
      fix n :: nat
      show "z^0 = 1" by simp
      show "z^(Suc n) = z * (z^n)" by simp
    qed

    lemma zpower_zmod: "((x::int) mod m)^y mod m = x^y mod m"
    apply (induct "y", auto)
    apply (rule zmod_zmult1_eq [THEN trans])
    apply (simp (no_asm_simp))
    apply (rule zmod_zmult_distrib [symmetric])
    done

    lemma zpower_zadd_distrib: "x^(y+z) = ((x^y)*(x^z)::int)"
      by (rule Power.power_add)

    lemma zpower_zpower: "(x^y)^z = (x^(y*z)::int)"
      by (rule Power.power_mult [symmetric])

    lemma zero_less_zpower_abs_iff [simp]:
         "(0 < (abs x)^n) = (x ≠ (0::int) | n=0)"
    apply (induct "n")
    apply (auto simp add: zero_less_mult_iff)
    done

    lemma zero_le_zpower_abs [simp]: "(0::int) <= (abs x)^n"
    apply (induct "n")
    apply (auto simp add: zero_le_mult_iff)
    done

    lemma int_power: "int (m^n) = (int m) ^ n"
      by (induct n, simp_all add: int_mult)

    text{*Compatibility binding*}
    lemmas zpower_int = int_power [symmetric]

    lemma zdiv_int: "int (a div b) = (int a) div (int b)"
    apply (subst split_div, auto)
    apply (subst split_zdiv, auto)
    apply (rule_tac a="int (b * i) + int j" and b="int b" and r="int j" and r'=ja in IntDiv.unique_quotient)
    apply (auto simp add: IntDiv.quorem_def int_eq_of_nat)
    done

    lemma zmod_int: "int (a mod b) = (int a) mod (int b)"
    apply (subst split_mod, auto)
    apply (subst split_zmod, auto)
    apply (rule_tac a="int (b * i) + int j" and b="int b" and q="int i" and q'=ia
           in unique_remainder)
    apply (auto simp add: IntDiv.quorem_def int_eq_of_nat)
    done

    text{*Suggested by Matthias Daum*}
    lemma int_power_div_base:
         "[|0 < m; 0 < k|] ==> k ^ m div k = (k::int) ^ (m - Suc 0)"
    apply (subgoal_tac "k ^ m = k ^ ((m - 1) + 1)")
     apply (erule ssubst)
     apply (simp only: power_add)
     apply simp_all
    done

    ML
    {*
    val quorem_def = thm "quorem_def";

    val unique_quotient = thm "unique_quotient";
    val unique_remainder = thm "unique_remainder";
    val adjust_eq = thm "adjust_eq";
    val posDivAlg_eqn = thm "posDivAlg_eqn";
    val posDivAlg_correct = thm "posDivAlg_correct";
    val negDivAlg_eqn = thm "negDivAlg_eqn";
    val negDivAlg_correct = thm "negDivAlg_correct";
    val quorem_0 = thm "quorem_0";
    val posDivAlg_0 = thm "posDivAlg_0";
    val negDivAlg_minus1 = thm "negDivAlg_minus1";
    val negateSnd_eq = thm "negateSnd_eq";
    val quorem_neg = thm "quorem_neg";
    val divAlg_correct = thm "divAlg_correct";
    val DIVISION_BY_ZERO = thm "DIVISION_BY_ZERO";
    val zmod_zdiv_equality = thm "zmod_zdiv_equality";
    val pos_mod_conj = thm "pos_mod_conj";
    val pos_mod_sign = thm "pos_mod_sign";
    val neg_mod_conj = thm "neg_mod_conj";
    val neg_mod_sign = thm "neg_mod_sign";
    val quorem_div_mod = thm "quorem_div_mod";
    val quorem_div = thm "quorem_div";
    val quorem_mod = thm "quorem_mod";
    val div_pos_pos_trivial = thm "div_pos_pos_trivial";
    val div_neg_neg_trivial = thm "div_neg_neg_trivial";
    val div_pos_neg_trivial = thm "div_pos_neg_trivial";
    val mod_pos_pos_trivial = thm "mod_pos_pos_trivial";
    val mod_neg_neg_trivial = thm "mod_neg_neg_trivial";
    val mod_pos_neg_trivial = thm "mod_pos_neg_trivial";
    val zdiv_zminus_zminus = thm "zdiv_zminus_zminus";
    val zmod_zminus_zminus = thm "zmod_zminus_zminus";
    val zdiv_zminus1_eq_if = thm "zdiv_zminus1_eq_if";
    val zmod_zminus1_eq_if = thm "zmod_zminus1_eq_if";
    val zdiv_zminus2 = thm "zdiv_zminus2";
    val zmod_zminus2 = thm "zmod_zminus2";
    val zdiv_zminus2_eq_if = thm "zdiv_zminus2_eq_if";
    val zmod_zminus2_eq_if = thm "zmod_zminus2_eq_if";
    val self_quotient = thm "self_quotient";
    val self_remainder = thm "self_remainder";
    val zdiv_self = thm "zdiv_self";
    val zmod_self = thm "zmod_self";
    val zdiv_zero = thm "zdiv_zero";
    val div_eq_minus1 = thm "div_eq_minus1";
    val zmod_zero = thm "zmod_zero";
    val zdiv_minus1 = thm "zdiv_minus1";
    val zmod_minus1 = thm "zmod_minus1";
    val div_pos_pos = thm "div_pos_pos";
    val mod_pos_pos = thm "mod_pos_pos";
    val div_neg_pos = thm "div_neg_pos";
    val mod_neg_pos = thm "mod_neg_pos";
    val div_pos_neg = thm "div_pos_neg";
    val mod_pos_neg = thm "mod_pos_neg";
    val div_neg_neg = thm "div_neg_neg";
    val mod_neg_neg = thm "mod_neg_neg";
    val zmod_1 = thm "zmod_1";
    val zdiv_1 = thm "zdiv_1";
    val zmod_minus1_right = thm "zmod_minus1_right";
    val zdiv_minus1_right = thm "zdiv_minus1_right";
    val zdiv_mono1 = thm "zdiv_mono1";
    val zdiv_mono1_neg = thm "zdiv_mono1_neg";
    val zdiv_mono2 = thm "zdiv_mono2";
    val zdiv_mono2_neg = thm "zdiv_mono2_neg";
    val zdiv_zmult1_eq = thm "zdiv_zmult1_eq";
    val zmod_zmult1_eq = thm "zmod_zmult1_eq";
    val zmod_zmult1_eq' = thm "zmod_zmult1_eq'";
    val zmod_zmult_distrib = thm "zmod_zmult_distrib";
    val zdiv_zmult_self1 = thm "zdiv_zmult_self1";
    val zdiv_zmult_self2 = thm "zdiv_zmult_self2";
    val zmod_zmult_self1 = thm "zmod_zmult_self1";
    val zmod_zmult_self2 = thm "zmod_zmult_self2";
    val zmod_eq_0_iff = thm "zmod_eq_0_iff";
    val zdiv_zadd1_eq = thm "zdiv_zadd1_eq";
    val zmod_zadd1_eq = thm "zmod_zadd1_eq";
    val mod_div_trivial = thm "mod_div_trivial";
    val mod_mod_trivial = thm "mod_mod_trivial";
    val zmod_zadd_left_eq = thm "zmod_zadd_left_eq";
    val zmod_zadd_right_eq = thm "zmod_zadd_right_eq";
    val zdiv_zadd_self1 = thm "zdiv_zadd_self1";
    val zdiv_zadd_self2 = thm "zdiv_zadd_self2";
    val zmod_zadd_self1 = thm "zmod_zadd_self1";
    val zmod_zadd_self2 = thm "zmod_zadd_self2";
    val zdiv_zmult2_eq = thm "zdiv_zmult2_eq";
    val zmod_zmult2_eq = thm "zmod_zmult2_eq";
    val zdiv_zmult_zmult1 = thm "zdiv_zmult_zmult1";
    val zdiv_zmult_zmult2 = thm "zdiv_zmult_zmult2";
    val zmod_zmult_zmult1 = thm "zmod_zmult_zmult1";
    val zmod_zmult_zmult2 = thm "zmod_zmult_zmult2";
    val pos_zdiv_mult_2 = thm "pos_zdiv_mult_2";
    val neg_zdiv_mult_2 = thm "neg_zdiv_mult_2";
    val zdiv_number_of_BIT = thm "zdiv_number_of_BIT";
    val pos_zmod_mult_2 = thm "pos_zmod_mult_2";
    val neg_zmod_mult_2 = thm "neg_zmod_mult_2";
    val zmod_number_of_BIT = thm "zmod_number_of_BIT";
    val div_neg_pos_less0 = thm "div_neg_pos_less0";
    val div_nonneg_neg_le0 = thm "div_nonneg_neg_le0";
    val pos_imp_zdiv_nonneg_iff = thm "pos_imp_zdiv_nonneg_iff";
    val neg_imp_zdiv_nonneg_iff = thm "neg_imp_zdiv_nonneg_iff";
    val pos_imp_zdiv_neg_iff = thm "pos_imp_zdiv_neg_iff";
    val neg_imp_zdiv_neg_iff = thm "neg_imp_zdiv_neg_iff";

    val zpower_zmod = thm "zpower_zmod";
    val zpower_zadd_distrib = thm "zpower_zadd_distrib";
    val zpower_zpower = thm "zpower_zpower";
    val zero_less_zpower_abs_iff = thm "zero_less_zpower_abs_iff";
    val zero_le_zpower_abs = thm "zero_le_zpower_abs";
    val zpower_int = thm "zpower_int";
    *}

    end

### Uniqueness and Monotonicity of Quotients and Remainders

lemma unique_quotient_lemma:

      [| b * q' + r' ≤ b * q + r; 0 ≤ r'; r' < b; r < b |] ==> q' ≤ q

lemma unique_quotient_lemma_neg:

      [| b * q' + r' ≤ b * q + r; r ≤ 0; b < r; b < r' |] ==> q ≤ q'

lemma unique_quotient:

      [| IntDiv.quorem ((a, b), q, r); IntDiv.quorem ((a, b), q', r'); b ≠ 0 |]
      ==> q = q'

lemma unique_remainder:

      [| IntDiv.quorem ((a, b), q, r); IntDiv.quorem ((a, b), q', r'); b ≠ 0 |]
      ==> r = r'

### Correctness of @{term posDivAlg}, the Algorithm for Non-Negative Dividends

lemma adjust_eq:

      adjust b (q, r) =
      (let diff = r - b in if 0 ≤ diff then (2 * q + 1, diff) else (2 * q, r))

lemma posDivAlg_eqn:

      0 < b
      ==> posDivAlg (a, b) =
          (if a < b then (0, a) else adjust b (posDivAlg (a, 2 * b)))

theorem posDivAlg_correct:

      [| 0 ≤ a; 0 < b |] ==> IntDiv.quorem ((a, b), posDivAlg (a, b))

### Correctness of @{term negDivAlg}, the Algorithm for Negative Dividends

lemma negDivAlg_eqn:

      0 < b
      ==> negDivAlg (a, b) =
          (if 0 ≤ a + b then (-1, a + b) else adjust b (negDivAlg (a, 2 * b)))

lemma negDivAlg_correct:

      [| a < 0; 0 < b |] ==> IntDiv.quorem ((a, b), negDivAlg (a, b))

### Existence Shown by Proving the Division Algorithm to be Correct

lemma quorem_0:

      b ≠ 0 ==> IntDiv.quorem ((0, b), 0, 0)

lemma posDivAlg_0:

      posDivAlg (0, b) = (0, 0)

lemma negDivAlg_minus1:

      negDivAlg (-1, b) = (-1, b - 1)

lemma negateSnd_eq:

      negateSnd (q, r) = (q, - r)

lemma quorem_neg:

      IntDiv.quorem ((- a, - b), qr) ==> IntDiv.quorem ((a, b), negateSnd qr)

lemma divAlg_correct:

      b ≠ 0 ==> IntDiv.quorem ((a, b), divAlg (a, b))

lemma DIVISION_BY_ZERO:

      a div 0 = 0 ∧ a mod 0 = a

lemma zmod_zdiv_equality:

      a = b * (a div b) + a mod b

lemma zdiv_zmod_equality:

      b * (a div b) + a mod b + k = a + k

lemma zdiv_zmod_equality2:

      a div b * b + a mod b + k = a + k

lemma pos_mod_conj:

      0 < b ==> 0 ≤ a mod b ∧ a mod b < b

lemmas pos_mod_sign:

      0 < b ==> 0 ≤ a mod b

and pos_mod_bound:

      0 < b ==> a mod b < b

lemmas pos_mod_sign:

      0 < b ==> 0 ≤ a mod b

and pos_mod_bound:

      0 < b ==> a mod b < b

lemma neg_mod_conj:

      b < 0 ==> a mod b ≤ 0 ∧ b < a mod b

lemmas neg_mod_sign:

      b < 0 ==> a mod b ≤ 0

and neg_mod_bound:

      b < 0 ==> b < a mod b

lemmas neg_mod_sign:

      b < 0 ==> a mod b ≤ 0

and neg_mod_bound:

      b < 0 ==> b < a mod b

### General Properties of div and mod

lemma quorem_div_mod:

      b ≠ 0 ==> IntDiv.quorem ((a, b), a div b, a mod b)

lemma quorem_div:

      [| IntDiv.quorem ((a, b), q, r); b ≠ 0 |] ==> a div b = q

lemma quorem_mod:

      [| IntDiv.quorem ((a, b), q, r); b ≠ 0 |] ==> a mod b = r

lemma div_pos_pos_trivial:

      [| 0 ≤ a; a < b |] ==> a div b = 0

lemma div_neg_neg_trivial:

      [| a ≤ 0; b < a |] ==> a div b = 0

lemma div_pos_neg_trivial:

      [| 0 < a; a + b ≤ 0 |] ==> a div b = -1

lemma mod_pos_pos_trivial:

      [| 0 ≤ a; a < b |] ==> a mod b = a

lemma mod_neg_neg_trivial:

      [| a ≤ 0; b < a |] ==> a mod b = a

lemma mod_pos_neg_trivial:

      [| 0 < a; a + b ≤ 0 |] ==> a mod b = a + b

lemma zdiv_zminus_zminus:

      - a div - b = a div b

lemma zmod_zminus_zminus:

      - a mod - b = - (a mod b)

### Laws for div and mod with Unary Minus

lemma zminus1_lemma:

      IntDiv.quorem ((a, b), q, r)
      ==> IntDiv.quorem
           ((- a, b), if r = 0 then - q else - q - 1, if r = 0 then 0 else b - r)

lemma zdiv_zminus1_eq_if:

      b ≠ 0 ==> - a div b = (if a mod b = 0 then - (a div b) else - (a div b) - 1)

lemma zmod_zminus1_eq_if:

      - a mod b = (if a mod b = 0 then 0 else b - a mod b)

lemma zdiv_zminus2:

      a div - b = - a div b

lemma zmod_zminus2:

      a mod - b = - (- a mod b)

lemma zdiv_zminus2_eq_if:

      b ≠ 0 ==> a div - b = (if a mod b = 0 then - (a div b) else - (a div b) - 1)

lemma zmod_zminus2_eq_if:

      a mod - b = (if a mod b = 0 then 0 else a mod b - b)

### Division of a Number by Itself

lemma self_quotient_aux1:

      [| 0 < a; a = r + a * q; r < a |] ==> 1 ≤ q

lemma self_quotient_aux2:

      [| 0 < a; a = r + a * q; 0 ≤ r |] ==> q ≤ 1

lemma self_quotient:

      [| IntDiv.quorem ((a, a), q, r); a ≠ 0 |] ==> q = 1

lemma self_remainder:

      [| IntDiv.quorem ((a, a), q, r); a ≠ 0 |] ==> r = 0

lemma zdiv_self:

      a ≠ 0 ==> a div a = 1

lemma zmod_self:

      a mod a = 0

### Computation of Division and Remainder

lemma zdiv_zero:

      0 div b = 0

lemma div_eq_minus1:

      0 < b ==> -1 div b = -1

lemma zmod_zero:

      0 mod b = 0

lemma zdiv_minus1:

      0 < b ==> -1 div b = -1

lemma zmod_minus1:

      0 < b ==> -1 mod b = b - 1

lemma div_pos_pos:

      [| 0 < a; 0 ≤ b |] ==> a div b = fst (posDivAlg (a, b))

lemma mod_pos_pos:

      [| 0 < a; 0 ≤ b |] ==> a mod b = snd (posDivAlg (a, b))

lemma div_neg_pos:

      [| a < 0; 0 < b |] ==> a div b = fst (negDivAlg (a, b))

lemma mod_neg_pos:

      [| a < 0; 0 < b |] ==> a mod b = snd (negDivAlg (a, b))

lemma div_pos_neg:

      [| 0 < a; b < 0 |] ==> a div b = fst (negateSnd (negDivAlg (- a, - b)))

lemma mod_pos_neg:

      [| 0 < a; b < 0 |] ==> a mod b = snd (negateSnd (negDivAlg (- a, - b)))

lemma div_neg_neg:

      [| a < 0; b ≤ 0 |] ==> a div b = fst (negateSnd (posDivAlg (- a, - b)))

lemma mod_neg_neg:

      [| a < 0; b ≤ 0 |] ==> a mod b = snd (negateSnd (posDivAlg (- a, - b)))

lemmas div_pos_pos_number_of:

      [| 0 < number_of v; 0 ≤ number_of w |]
      ==> number_of v div number_of w = fst (posDivAlg (number_of v, number_of w))

lemmas div_pos_pos_number_of:

      [| 0 < number_of v; 0 ≤ number_of w |]
      ==> number_of v div number_of w = fst (posDivAlg (number_of v, number_of w))

lemmas div_neg_pos_number_of:

      [| number_of v < 0; 0 < number_of w |]
      ==> number_of v div number_of w = fst (negDivAlg (number_of v, number_of w))

lemmas div_neg_pos_number_of:

      [| number_of v < 0; 0 < number_of w |]
      ==> number_of v div number_of w = fst (negDivAlg (number_of v, number_of w))

lemmas div_pos_neg_number_of:

      [| 0 < number_of v; number_of w < 0 |]
      ==> number_of v div number_of w =
          fst (negateSnd (negDivAlg (- number_of v, - number_of w)))

lemmas div_pos_neg_number_of:

      [| 0 < number_of v; number_of w < 0 |]
      ==> number_of v div number_of w =
          fst (negateSnd (negDivAlg (- number_of v, - number_of w)))

lemmas div_neg_neg_number_of:

      [| number_of v < 0; number_of w ≤ 0 |]
      ==> number_of v div number_of w =
          fst (negateSnd (posDivAlg (- number_of v, - number_of w)))

lemmas div_neg_neg_number_of:

      [| number_of v < 0; number_of w ≤ 0 |]
      ==> number_of v div number_of w =
          fst (negateSnd (posDivAlg (- number_of v, - number_of w)))

lemmas mod_pos_pos_number_of:

      [| 0 < number_of v; 0 ≤ number_of w |]
      ==> number_of v mod number_of w = snd (posDivAlg (number_of v, number_of w))

lemmas mod_pos_pos_number_of:

      [| 0 < number_of v; 0 ≤ number_of w |]
      ==> number_of v mod number_of w = snd (posDivAlg (number_of v, number_of w))

lemmas mod_neg_pos_number_of:

      [| number_of v < 0; 0 < number_of w |]
      ==> number_of v mod number_of w = snd (negDivAlg (number_of v, number_of w))

lemmas mod_neg_pos_number_of:

      [| number_of v < 0; 0 < number_of w |]
      ==> number_of v mod number_of w = snd (negDivAlg (number_of v, number_of w))

lemmas mod_pos_neg_number_of:

      [| 0 < number_of v; number_of w < 0 |]
      ==> number_of v mod number_of w =
          snd (negateSnd (negDivAlg (- number_of v, - number_of w)))

lemmas mod_pos_neg_number_of:

      [| 0 < number_of v; number_of w < 0 |]
      ==> number_of v mod number_of w =
          snd (negateSnd (negDivAlg (- number_of v, - number_of w)))

lemmas mod_neg_neg_number_of:

      [| number_of v < 0; number_of w ≤ 0 |]
      ==> number_of v mod number_of w =
          snd (negateSnd (posDivAlg (- number_of v, - number_of w)))

lemmas mod_neg_neg_number_of:

      [| number_of v < 0; number_of w ≤ 0 |]
      ==> number_of v mod number_of w =
          snd (negateSnd (posDivAlg (- number_of v, - number_of w)))

lemmas posDivAlg_eqn_number_of:

      0 < number_of v
      ==> posDivAlg (number_of w, number_of v) =
          (if number_of w < number_of v then (0, number_of w)
           else adjust (number_of v) (posDivAlg (number_of w, 2 * number_of v)))

lemmas posDivAlg_eqn_number_of:

      0 < number_of v
      ==> posDivAlg (number_of w, number_of v) =
          (if number_of w < number_of v then (0, number_of w)
           else adjust (number_of v) (posDivAlg (number_of w, 2 * number_of v)))

lemmas negDivAlg_eqn_number_of:

      0 < number_of v
      ==> negDivAlg (number_of w, number_of v) =
          (if 0 ≤ number_of w + number_of v then (-1, number_of w + number_of v)
           else adjust (number_of v) (negDivAlg (number_of w, 2 * number_of v)))

lemmas negDivAlg_eqn_number_of:

      0 < number_of v
      ==> negDivAlg (number_of w, number_of v) =
          (if 0 ≤ number_of w + number_of v then (-1, number_of w + number_of v)
           else adjust (number_of v) (negDivAlg (number_of w, 2 * number_of v)))

lemma zmod_1:

      a mod 1 = 0

lemma zdiv_1:

      a div 1 = a

lemma zmod_minus1_right:

      a mod -1 = 0

lemma zdiv_minus1_right:

      a div -1 = - a

lemmas div_pos_pos_1_number_of:

      0 ≤ number_of w ==> 1 div number_of w = fst (posDivAlg (1, number_of w))

lemmas div_pos_pos_1_number_of:

      0 ≤ number_of w ==> 1 div number_of w = fst (posDivAlg (1, number_of w))

lemmas div_pos_neg_1_number_of:

      number_of w < 0
      ==> 1 div number_of w = fst (negateSnd (negDivAlg (- 1, - number_of w)))

lemmas div_pos_neg_1_number_of:

      number_of w < 0
      ==> 1 div number_of w = fst (negateSnd (negDivAlg (- 1, - number_of w)))

lemmas mod_pos_pos_1_number_of:

      0 ≤ number_of w ==> 1 mod number_of w = snd (posDivAlg (1, number_of w))

lemmas mod_pos_pos_1_number_of:

      0 ≤ number_of w ==> 1 mod number_of w = snd (posDivAlg (1, number_of w))

lemmas mod_pos_neg_1_number_of:

      number_of w < 0
      ==> 1 mod number_of w = snd (negateSnd (negDivAlg (- 1, - number_of w)))

lemmas mod_pos_neg_1_number_of:

      number_of w < 0
      ==> 1 mod number_of w = snd (negateSnd (negDivAlg (- 1, - number_of w)))

lemmas posDivAlg_eqn_1_number_of:

      0 < number_of w
      ==> posDivAlg (1, number_of w) =
          (if 1 < number_of w then (0, 1)
           else adjust (number_of w) (posDivAlg (1, 2 * number_of w)))

lemmas posDivAlg_eqn_1_number_of:

      0 < number_of w
      ==> posDivAlg (1, number_of w) =
          (if 1 < number_of w then (0, 1)
           else adjust (number_of w) (posDivAlg (1, 2 * number_of w)))

lemmas negDivAlg_eqn_1_number_of:

      0 < number_of w
      ==> negDivAlg (1, number_of w) =
          (if 0 ≤ 1 + number_of w then (-1, 1 + number_of w)
           else adjust (number_of w) (negDivAlg (1, 2 * number_of w)))

lemmas negDivAlg_eqn_1_number_of:

      0 < number_of w
      ==> negDivAlg (1, number_of w) =
          (if 0 ≤ 1 + number_of w then (-1, 1 + number_of w)
           else adjust (number_of w) (negDivAlg (1, 2 * number_of w)))

### Monotonicity in the First Argument (Dividend)

lemma zdiv_mono1:

      [| a ≤ a'; 0 < b |] ==> a div b ≤ a' div b

lemma zdiv_mono1_neg:

      [| a ≤ a'; b < 0 |] ==> a' div b ≤ a div b

### Monotonicity in the Second Argument (Divisor)

lemma q_pos_lemma:

      [| 0 ≤ b' * q' + r'; r' < b'; 0 < b' |] ==> 0 ≤ q'

lemma zdiv_mono2_lemma:

      [| b * q + r = b' * q' + r'; 0 ≤ b' * q' + r'; r' < b'; 0 ≤ r; 0 < b'; b' ≤ b |]
      ==> q ≤ q'

lemma zdiv_mono2:

      [| 0 ≤ a; 0 < b'; b' ≤ b |] ==> a div b ≤ a div b'

lemma q_neg_lemma:

      [| b' * q' + r' < 0; 0 ≤ r'; 0 < b' |] ==> q' ≤ 0

lemma zdiv_mono2_neg_lemma:

      [| b * q + r = b' * q' + r'; b' * q' + r' < 0; r < b; 0 ≤ r'; 0 < b'; b' ≤ b |]
      ==> q' ≤ q

lemma zdiv_mono2_neg:

      [| a < 0; 0 < b'; b' ≤ b |] ==> a div b' ≤ a div b

### More Algebraic Laws for div and mod

lemma zmult1_lemma:

      [| IntDiv.quorem ((b, c), q, r); c ≠ 0 |]
      ==> IntDiv.quorem ((a * b, c), a * q + a * r div c, a * r mod c)

lemma zdiv_zmult1_eq:

      a * b div c = a * (b div c) + a * (b mod c) div c

lemma zmod_zmult1_eq:

      a * b mod c = a * (b mod c) mod c

lemma zmod_zmult1_eq':

      a * b mod c = a mod c * b mod c

lemma zmod_zmult_distrib:

      a * b mod c = a mod c * (b mod c) mod c

lemma zdiv_zmult_self1:

      b ≠ 0 ==> a * b div b = a

lemma zdiv_zmult_self2:

      b ≠ 0 ==> b * a div b = a

lemma zmod_zmult_self1:

      a * b mod b = 0

lemma zmod_zmult_self2:

      b * a mod b = 0

lemma zmod_eq_0_iff:

      (m mod d = 0) = (∃q. m = d * q)

lemmas zmod_eq_0D:

      m1 mod d1 = 0 ==> ∃q. m1 = d1 * q

lemmas zmod_eq_0D:

      m1 mod d1 = 0 ==> ∃q. m1 = d1 * q

lemma zadd1_lemma:

      [| IntDiv.quorem ((a, c), aq, ar); IntDiv.quorem ((b, c), bq, br); c ≠ 0 |]
      ==> IntDiv.quorem ((a + b, c), aq + bq + (ar + br) div c, (ar + br) mod c)

lemma zdiv_zadd1_eq:

      (a + b) div c = a div c + b div c + (a mod c + b mod c) div c

lemma zmod_zadd1_eq:

      (a + b) mod c = (a mod c + b mod c) mod c

lemma mod_div_trivial:

      a mod b div b = 0

lemma mod_mod_trivial:

      a mod b mod b = a mod b

lemma zmod_zadd_left_eq:

      (a + b) mod c = (a mod c + b) mod c

lemma zmod_zadd_right_eq:

      (a + b) mod c = (a + b mod c) mod c

lemma zdiv_zadd_self1:

      a ≠ 0 ==> (a + b) div a = b div a + 1

lemma zdiv_zadd_self2:

      a ≠ 0 ==> (b + a) div a = b div a + 1

lemma zmod_zadd_self1:

      (a + b) mod a = b mod a

lemma zmod_zadd_self2:

      (b + a) mod a = b mod a

### Proving @{term "a div (b*c) = (a div b) div c"}

lemma zmult2_lemma_aux1:

      [| 0 < c; b < r; r ≤ 0 |] ==> b * c < b * (q mod c) + r

lemma zmult2_lemma_aux2:

      [| 0 < c; b < r; r ≤ 0 |] ==> b * (q mod c) + r ≤ 0

lemma zmult2_lemma_aux3:

      [| 0 < c; 0 ≤ r; r < b |] ==> 0 ≤ b * (q mod c) + r

lemma zmult2_lemma_aux4:

      [| 0 < c; 0 ≤ r; r < b |] ==> b * (q mod c) + r < b * c

lemma zmult2_lemma:

      [| IntDiv.quorem ((a, b), q, r); b ≠ 0; 0 < c |]
      ==> IntDiv.quorem ((a, b * c), q div c, b * (q mod c) + r)

lemma zdiv_zmult2_eq:

      0 < c ==> a div (b * c) = a div b div c

lemma zmod_zmult2_eq:

      0 < c ==> a mod (b * c) = b * (a div b mod c) + a mod b

### Cancellation of Common Factors in div

lemma zdiv_zmult_zmult1_aux1:

      [| 0 < b; c ≠ 0 |] ==> c * a div (c * b) = a div b

lemma zdiv_zmult_zmult1_aux2:

      [| b < 0; c ≠ 0 |] ==> c * a div (c * b) = a div b

lemma zdiv_zmult_zmult1:

      c ≠ 0 ==> c * a div (c * b) = a div b

lemma zdiv_zmult_zmult2:

      c ≠ 0 ==> a * c div (b * c) = a div b

### Distribution of Factors over mod

lemma zmod_zmult_zmult1_aux1:

      [| 0 < b; c ≠ 0 |] ==> c * a mod (c * b) = c * (a mod b)

lemma zmod_zmult_zmult1_aux2:

      [| b < 0; c ≠ 0 |] ==> c * a mod (c * b) = c * (a mod b)

lemma zmod_zmult_zmult1:

      c * a mod (c * b) = c * (a mod b)

lemma zmod_zmult_zmult2:

      a * c mod (b * c) = a mod b * c

### Splitting Rules for div and mod

lemma split_pos_lemma:

      0 < k
      ==> P (n div k) (n mod k) = (∀i j. 0 ≤ j ∧ j < k ∧ n = k * i + j --> P i j)

lemma split_neg_lemma:

      k < 0
      ==> P (n div k) (n mod k) = (∀i j. k < j ∧ j ≤ 0 ∧ n = k * i + j --> P i j)

lemma split_zdiv:

      P (n div k) =
      ((k = 0 --> P 0) ∧
       (0 < k --> (∀i j. 0 ≤ j ∧ j < k ∧ n = k * i + j --> P i)) ∧
       (k < 0 --> (∀i j. k < j ∧ j ≤ 0 ∧ n = k * i + j --> P i)))

lemma split_zmod:

      P (n mod k) =
      ((k = 0 --> P n) ∧
       (0 < k --> (∀i j. 0 ≤ j ∧ j < k ∧ n = k * i + j --> P j)) ∧
       (k < 0 --> (∀i j. k < j ∧ j ≤ 0 ∧ n = k * i + j --> P j)))

### Speeding up the Division Algorithm with Shifting

lemma pos_zdiv_mult_2:

      0 ≤ a ==> (1 + 2 * b) div (2 * a) = b div a

lemma neg_zdiv_mult_2:

      a ≤ 0 ==> (1 + 2 * b) div (2 * a) = (b + 1) div a

lemma not_0_le_lemma:

      ¬ 0 ≤ x ==> x ≤ 0

lemma zdiv_number_of_BIT:

      number_of (v BIT b) div number_of (w BIT bit.B0) =
      (if b = bit.B0 ∨ 0 ≤ number_of w then number_of v div number_of w
       else (number_of v + 1) div number_of w)

### Computing mod by Shifting (proofs resemble those for div)

lemma pos_zmod_mult_2:

      0 ≤ a ==> (1 + 2 * b) mod (2 * a) = 1 + 2 * (b mod a)

lemma neg_zmod_mult_2:

      a ≤ 0 ==> (1 + 2 * b) mod (2 * a) = 2 * ((b + 1) mod a) - 1

lemma zmod_number_of_BIT:

      number_of (v BIT b) mod number_of (w BIT bit.B0) =
      (case b of bit.B0 => 2 * (number_of v mod number_of w)
       | bit.B1 =>
           if 0 ≤ number_of w then 2 * (number_of v mod number_of w) + 1
           else 2 * ((number_of v + 1) mod number_of w) - 1)

### Quotients of Signs

lemma div_neg_pos_less0:

      [| a < 0; 0 < b |] ==> a div b < 0

lemma div_nonneg_neg_le0:

      [| 0 ≤ a; b < 0 |] ==> a div b ≤ 0

lemma pos_imp_zdiv_nonneg_iff:

      0 < b ==> (0 ≤ a div b) = (0 ≤ a)

lemma neg_imp_zdiv_nonneg_iff:

      b < 0 ==> (0 ≤ a div b) = (a ≤ 0)

lemma pos_imp_zdiv_neg_iff:

      0 < b ==> (a div b < 0) = (a < 0)

lemma neg_imp_zdiv_neg_iff:

      b < 0 ==> (a div b < 0) = (0 < a)

### The Divides Relation

lemma zdvd_iff_zmod_eq_0:

      (m dvd n) = (n mod m = 0)

lemma zdvd_0_right:

      m dvd 0

lemma zdvd_0_left:

      (0 dvd m) = (m = 0)

lemma zdvd_1_left:

      1 dvd m

lemma zdvd_refl:

      m dvd m

lemma zdvd_trans:

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

lemma zdvd_zminus_iff:

      (m dvd - n) = (m dvd n)

lemma zdvd_zminus2_iff:

      (- m dvd n) = (m dvd n)

lemma zdvd_anti_sym:

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

lemma zdvd_zadd:

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

lemma zdvd_zdiff:

      [| k dvd m; k dvd n |] ==> k dvd m - n

lemma zdvd_zdiffD:

      [| k dvd m - n; k dvd n |] ==> k dvd m

lemma zdvd_zmult:

      k dvd n ==> k dvd m * n

lemma zdvd_zmult2:

      k dvd m ==> k dvd m * n

lemma zdvd_triv_right:

      k dvd m * k

lemma zdvd_triv_left:

      k dvd k * m

lemma zdvd_zmultD2:

      j * k dvd n ==> j dvd n

lemma zdvd_zmultD:

      j * k dvd n ==> k dvd n

lemma zdvd_zmult_mono:

      [| i dvd m; j dvd n |] ==> i * j dvd m * n

lemma zdvd_reduce:

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

lemma zdvd_zmod:

      [| f dvd m; f dvd n |] ==> f dvd m mod n

lemma zdvd_zmod_imp_zdvd:

      [| k dvd m mod n; k dvd n |] ==> k dvd m

lemma zdvd_not_zless:

      [| 0 < m; m < n |] ==> ¬ n dvd m

lemma int_dvd_iff:

      (int m dvd z) = (m dvd nat ¦z¦)

lemma dvd_int_iff:

      (z dvd int m) = (nat ¦z¦ dvd m)

lemma nat_dvd_iff:

      (nat z dvd m) = (if 0 ≤ z then z dvd int m else m = 0)

lemma zminus_dvd_iff:

      (- z dvd w) = (z dvd w)

lemma dvd_zminus_iff:

      (z dvd - w) = (z dvd w)

lemma zdvd_imp_le:

      [| z dvd n; 0 < n |] ==> z ≤ n

### Integer Powers

lemma zpower_zmod:

      (x mod m) ^ y mod m = x ^ y mod m

lemma zpower_zadd_distrib:

      x ^ (y + z) = x ^ y * x ^ z

lemma zpower_zpower:

      (x ^ y) ^ z = x ^ (y * z)

lemma zero_less_zpower_abs_iff:

      (0 < ¦x¦ ^ n) = (x ≠ 0 ∨ n = 0)

lemma zero_le_zpower_abs:

      0 ≤ ¦x¦ ^ n

lemma int_power:

      int (m ^ n) = int m ^ n

lemmas zpower_int:

      int m1 ^ n1 = int (m1 ^ n1)

lemmas zpower_int:

      int m1 ^ n1 = int (m1 ^ n1)

lemma zdiv_int:

      int (a div b) = int a div int b

lemma zmod_int:

      int (a mod b) = int a mod int b

lemma int_power_div_base:

      [| 0 < m; 0 < k |] ==> k ^ m div k = k ^ (m - Suc 0)