Theory IntArith (Isabelle2005: October 2005)

# Theory IntArith

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theory IntArith
imports Numeral
uses (int_arith1.ML)
begin

    (*  Title:      HOL/Integ/IntArith.thy
        ID:         $Id: IntArith.thy,v 1.33 2005/09/17 16:25:11 wenzelm Exp $
        Authors:    Larry Paulson and Tobias Nipkow
    *)

    header {* Integer arithmetic *}

    theory IntArith
    imports Numeral
    uses ("int_arith1.ML")
    begin

    text{*Duplicate: can't understand why it's necessary*}
    declare numeral_0_eq_0 [simp]

    subsection{*Instantiating Binary Arithmetic for the Integers*}

    instance
      int :: number ..

    defs (overloaded)
      int_number_of_def: "(number_of w :: int) == of_int (Rep_Bin w)"
        --{*the type constraint is essential!*}

    instance int :: number_ring
    by (intro_classes, simp add: int_number_of_def)

    subsection{*Inequality Reasoning for the Arithmetic Simproc*}

    lemma add_numeral_0: "Numeral0 + a = (a::'a::number_ring)"
    by simp

    lemma add_numeral_0_right: "a + Numeral0 = (a::'a::number_ring)"
    by simp

    lemma mult_numeral_1: "Numeral1 * a = (a::'a::number_ring)"
    by simp

    lemma mult_numeral_1_right: "a * Numeral1 = (a::'a::number_ring)"
    by simp

    text{*Theorem lists for the cancellation simprocs. The use of binary numerals
    for 0 and 1 reduces the number of special cases.*}

    lemmas add_0s = add_numeral_0 add_numeral_0_right
    lemmas mult_1s = mult_numeral_1 mult_numeral_1_right
                     mult_minus1 mult_minus1_right

    subsection{*Special Arithmetic Rules for Abstract 0 and 1*}

    text{*Arithmetic computations are defined for binary literals, which leaves 0
    and 1 as special cases. Addition already has rules for 0, but not 1.
    Multiplication and unary minus already have rules for both 0 and 1.*}

    lemma binop_eq: "[|f x y = g x y; x = x'; y = y'|] ==> f x' y' = g x' y'"
    by simp

    lemmas add_number_of_eq = number_of_add [symmetric]

    text{*Allow 1 on either or both sides*}
    lemma one_add_one_is_two: "1 + 1 = (2::'a::number_ring)"
    by (simp del: numeral_1_eq_1 add: numeral_1_eq_1 [symmetric] add_number_of_eq)

    lemmas add_special =
        one_add_one_is_two
        binop_eq [of "op +", OF add_number_of_eq numeral_1_eq_1 refl, standard]
        binop_eq [of "op +", OF add_number_of_eq refl numeral_1_eq_1, standard]

    text{*Allow 1 on either or both sides (1-1 already simplifies to 0)*}
    lemmas diff_special =
        binop_eq [of "op -", OF diff_number_of_eq numeral_1_eq_1 refl, standard]
        binop_eq [of "op -", OF diff_number_of_eq refl numeral_1_eq_1, standard]

    text{*Allow 0 or 1 on either side with a binary numeral on the other*}
    lemmas eq_special =
        binop_eq [of "op =", OF eq_number_of_eq numeral_0_eq_0 refl, standard]
        binop_eq [of "op =", OF eq_number_of_eq numeral_1_eq_1 refl, standard]
        binop_eq [of "op =", OF eq_number_of_eq refl numeral_0_eq_0, standard]
        binop_eq [of "op =", OF eq_number_of_eq refl numeral_1_eq_1, standard]

    text{*Allow 0 or 1 on either side with a binary numeral on the other*}
    lemmas less_special =
      binop_eq [of "op <", OF less_number_of_eq_neg numeral_0_eq_0 refl, standard]
      binop_eq [of "op <", OF less_number_of_eq_neg numeral_1_eq_1 refl, standard]
      binop_eq [of "op <", OF less_number_of_eq_neg refl numeral_0_eq_0, standard]
      binop_eq [of "op <", OF less_number_of_eq_neg refl numeral_1_eq_1, standard]

    text{*Allow 0 or 1 on either side with a binary numeral on the other*}
    lemmas le_special =
        binop_eq [of "op ≤", OF le_number_of_eq numeral_0_eq_0 refl, standard]
        binop_eq [of "op ≤", OF le_number_of_eq numeral_1_eq_1 refl, standard]
        binop_eq [of "op ≤", OF le_number_of_eq refl numeral_0_eq_0, standard]
        binop_eq [of "op ≤", OF le_number_of_eq refl numeral_1_eq_1, standard]

    lemmas arith_special =
           add_special diff_special eq_special less_special le_special

    use "int_arith1.ML"
    setup int_arith_setup

    subsection{*Lemmas About Small Numerals*}

    lemma of_int_m1 [simp]: "of_int -1 = (-1 :: 'a :: number_ring)"
    proof -
      have "(of_int -1 :: 'a) = of_int (- 1)" by simp
      also have "... = - of_int 1" by (simp only: of_int_minus)
      also have "... = -1" by simp
      finally show ?thesis .
    qed

    lemma abs_minus_one [simp]: "abs (-1) = (1::'a::{ordered_idom,number_ring})"
    by (simp add: abs_if)

    lemma abs_power_minus_one [simp]:
         "abs(-1 ^ n) = (1::'a::{ordered_idom,number_ring,recpower})"
    by (simp add: power_abs)

    lemma of_int_number_of_eq:
         "of_int (number_of v) = (number_of v :: 'a :: number_ring)"
    by (simp add: number_of_eq)

    text{*Lemmas for specialist use, NOT as default simprules*}
    lemma mult_2: "2 * z = (z+z::'a::number_ring)"
    proof -
      have "2*z = (1 + 1)*z" by simp
      also have "... = z+z" by (simp add: left_distrib)
      finally show ?thesis .
    qed

    lemma mult_2_right: "z * 2 = (z+z::'a::number_ring)"
    by (subst mult_commute, rule mult_2)

    subsection{*More Inequality Reasoning*}

    lemma zless_add1_eq: "(w < z + (1::int)) = (w<z | w=z)"
    by arith

    lemma add1_zle_eq: "(w + (1::int) ≤ z) = (w<z)"
    by arith

    lemma zle_diff1_eq [simp]: "(w ≤ z - (1::int)) = (w<z)"
    by arith

    lemma zle_add1_eq_le [simp]: "(w < z + (1::int)) = (w≤z)"
    by arith

    lemma int_one_le_iff_zero_less: "((1::int) ≤ z) = (0 < z)"
    by arith

    subsection{*The Functions @{term nat} and @{term int}*}

    text{*Simplify the terms @{term "int 0"}, @{term "int(Suc 0)"} and
      @{term "w + - z"}*}
    declare Zero_int_def [symmetric, simp]
    declare One_int_def [symmetric, simp]

    text{*cooper.ML refers to this theorem*}
    lemmas diff_int_def_symmetric = diff_int_def [symmetric, simp]

    lemma nat_0: "nat 0 = 0"
    by (simp add: nat_eq_iff)

    lemma nat_1: "nat 1 = Suc 0"
    by (subst nat_eq_iff, simp)

    lemma nat_2: "nat 2 = Suc (Suc 0)"
    by (subst nat_eq_iff, simp)

    lemma one_less_nat_eq [simp]: "(Suc 0 < nat z) = (1 < z)"
    apply (insert zless_nat_conj [of 1 z])
    apply (auto simp add: nat_1)
    done

    text{*This simplifies expressions of the form @{term "int n = z"} where
          z is an integer literal.*}
    lemmas int_eq_iff_number_of = int_eq_iff [of _ "number_of v", standard]
    declare int_eq_iff_number_of [simp]

    lemma split_nat [arith_split]:
      "P(nat(i::int)) = ((∀n. i = int n --> P n) & (i < 0 --> P 0))"
      (is "?P = (?L & ?R)")
    proof (cases "i < 0")
      case True thus ?thesis by simp
    next
      case False
      have "?P = ?L"
      proof
        assume ?P thus ?L using False by clarsimp
      next
        assume ?L thus ?P using False by simp
      qed
      with False show ?thesis by simp
    qed

    (*Analogous to zadd_int*)
    lemma zdiff_int: "n ≤ m ==> int m - int n = int (m-n)"
    by (induct m n rule: diff_induct, simp_all)

    lemma nat_mult_distrib: "(0::int) ≤ z ==> nat (z*z') = nat z * nat z'"
    apply (case_tac "0 ≤ z'")
    apply (rule inj_int [THEN injD])
    apply (simp add: int_mult zero_le_mult_iff)
    apply (simp add: mult_le_0_iff)
    done

    lemma nat_mult_distrib_neg: "z ≤ (0::int) ==> nat(z*z') = nat(-z) * nat(-z')"
    apply (rule trans)
    apply (rule_tac [2] nat_mult_distrib, auto)
    done

    lemma nat_abs_mult_distrib: "nat (abs (w * z)) = nat (abs w) * nat (abs z)"
    apply (case_tac "z=0 | w=0")
    apply (auto simp add: abs_if nat_mult_distrib [symmetric]
                          nat_mult_distrib_neg [symmetric] mult_less_0_iff)
    done

    subsection "Induction principles for int"

                         (* `set:int': dummy construction *)
    theorem int_ge_induct[case_names base step,induct set:int]:
      assumes ge: "k ≤ (i::int)" and
            base: "P(k)" and
            step: "!!i. [|k ≤ i; P i|] ==> P(i+1)"
      shows "P i"
    proof -
      { fix n have "!!i::int. n = nat(i-k) ==> k ≤ i ==> P i"
        proof (induct n)
          case 0
          hence "i = k" by arith
          thus "P i" using base by simp
        next
          case (Suc n)
          hence "n = nat((i - 1) - k)" by arith
          moreover
          have ki1: "k ≤ i - 1" using Suc.prems by arith
          ultimately
          have "P(i - 1)" by(rule Suc.hyps)
          from step[OF ki1 this] show ?case by simp
        qed
      }
      with ge show ?thesis by fast
    qed

                         (* `set:int': dummy construction *)
    theorem int_gr_induct[case_names base step,induct set:int]:
      assumes gr: "k < (i::int)" and
            base: "P(k+1)" and
            step: "!!i. [|k < i; P i|] ==> P(i+1)"
      shows "P i"
    apply(rule int_ge_induct[of "k + 1"])
      using gr apply arith
     apply(rule base)
    apply (rule step, simp+)
    done

    theorem int_le_induct[consumes 1,case_names base step]:
      assumes le: "i ≤ (k::int)" and
            base: "P(k)" and
            step: "!!i. [|i ≤ k; P i|] ==> P(i - 1)"
      shows "P i"
    proof -
      { fix n have "!!i::int. n = nat(k-i) ==> i ≤ k ==> P i"
        proof (induct n)
          case 0
          hence "i = k" by arith
          thus "P i" using base by simp
        next
          case (Suc n)
          hence "n = nat(k - (i+1))" by arith
          moreover
          have ki1: "i + 1 ≤ k" using Suc.prems by arith
          ultimately
          have "P(i+1)" by(rule Suc.hyps)
          from step[OF ki1 this] show ?case by simp
        qed
      }
      with le show ?thesis by fast
    qed

    theorem int_less_induct [consumes 1,case_names base step]:
      assumes less: "(i::int) < k" and
            base: "P(k - 1)" and
            step: "!!i. [|i < k; P i|] ==> P(i - 1)"
      shows "P i"
    apply(rule int_le_induct[of _ "k - 1"])
      using less apply arith
     apply(rule base)
    apply (rule step, simp+)
    done

    subsection{*Intermediate value theorems*}

    lemma int_val_lemma:
         "(∀i<n::nat. abs(f(i+1) - f i) ≤ 1) -->
          f 0 ≤ k --> k ≤ f n --> (∃i ≤ n. f i = (k::int))"
    apply (induct_tac "n", simp)
    apply (intro strip)
    apply (erule impE, simp)
    apply (erule_tac x = n in allE, simp)
    apply (case_tac "k = f (n+1) ")
     apply force
    apply (erule impE)
     apply (simp add: abs_if split add: split_if_asm)
    apply (blast intro: le_SucI)
    done

    lemmas nat0_intermed_int_val = int_val_lemma [rule_format (no_asm)]

    lemma nat_intermed_int_val:
         "[| ∀i. m ≤ i & i < n --> abs(f(i + 1::nat) - f i) ≤ 1; m < n;
             f m ≤ k; k ≤ f n |] ==> ? i. m ≤ i & i ≤ n & f i = (k::int)"
    apply (cut_tac n = "n-m" and f = "%i. f (i+m) " and k = k
           in int_val_lemma)
    apply simp
    apply (erule impE)
     apply (intro strip)
     apply (erule_tac x = "i+m" in allE, arith)
    apply (erule exE)
    apply (rule_tac x = "i+m" in exI, arith)
    done

    subsection{*Products and 1, by T. M. Rasmussen*}

    lemma zabs_less_one_iff [simp]: "(¦z¦ < 1) = (z = (0::int))"
    by arith

    lemma abs_zmult_eq_1: "(¦m * n¦ = 1) ==> ¦m¦ = (1::int)"
    apply (case_tac "¦n¦=1")
    apply (simp add: abs_mult)
    apply (rule ccontr)
    apply (auto simp add: linorder_neq_iff abs_mult)
    apply (subgoal_tac "2 ≤ ¦m¦ & 2 ≤ ¦n¦")
     prefer 2 apply arith
    apply (subgoal_tac "2*2 ≤ ¦m¦ * ¦n¦", simp)
    apply (rule mult_mono, auto)
    done

    lemma pos_zmult_eq_1_iff_lemma: "(m * n = 1) ==> m = (1::int) | m = -1"
    by (insert abs_zmult_eq_1 [of m n], arith)

    lemma pos_zmult_eq_1_iff: "0 < (m::int) ==> (m * n = 1) = (m = 1 & n = 1)"
    apply (auto dest: pos_zmult_eq_1_iff_lemma)
    apply (simp add: mult_commute [of m])
    apply (frule pos_zmult_eq_1_iff_lemma, auto)
    done

    lemma zmult_eq_1_iff: "(m*n = (1::int)) = ((m = 1 & n = 1) | (m = -1 & n = -1))"
    apply (rule iffI)
     apply (frule pos_zmult_eq_1_iff_lemma)
     apply (simp add: mult_commute [of m])
     apply (frule pos_zmult_eq_1_iff_lemma, auto)
    done

    ML
    {*
    val zle_diff1_eq = thm "zle_diff1_eq";
    val zle_add1_eq_le = thm "zle_add1_eq_le";
    val nonneg_eq_int = thm "nonneg_eq_int";
    val abs_minus_one = thm "abs_minus_one";
    val of_int_number_of_eq = thm"of_int_number_of_eq";
    val nat_eq_iff = thm "nat_eq_iff";
    val nat_eq_iff2 = thm "nat_eq_iff2";
    val nat_less_iff = thm "nat_less_iff";
    val int_eq_iff = thm "int_eq_iff";
    val nat_0 = thm "nat_0";
    val nat_1 = thm "nat_1";
    val nat_2 = thm "nat_2";
    val nat_less_eq_zless = thm "nat_less_eq_zless";
    val nat_le_eq_zle = thm "nat_le_eq_zle";

    val nat_intermed_int_val = thm "nat_intermed_int_val";
    val pos_zmult_eq_1_iff = thm "pos_zmult_eq_1_iff";
    val zmult_eq_1_iff = thm "zmult_eq_1_iff";
    val nat_add_distrib = thm "nat_add_distrib";
    val nat_diff_distrib = thm "nat_diff_distrib";
    val nat_mult_distrib = thm "nat_mult_distrib";
    val nat_mult_distrib_neg = thm "nat_mult_distrib_neg";
    val nat_abs_mult_distrib = thm "nat_abs_mult_distrib";
    *}

    end

### Instantiating Binary Arithmetic for the Integers

### Inequality Reasoning for the Arithmetic Simproc

lemma add_numeral_0:

      Numeral0 + a = a

lemma add_numeral_0_right:

      a + Numeral0 = a

lemma mult_numeral_1:

      Numeral1 * a = a

lemma mult_numeral_1_right:

      a * Numeral1 = a

lemmas add_0s:

      Numeral0 + a = a

      a + Numeral0 = a

lemmas add_0s:

      Numeral0 + a = a

      a + Numeral0 = a

lemmas mult_1s:

      Numeral1 * a = a

      a * Numeral1 = a

      (-1::'a) * z = - z

      z * (-1::'a) = - z

lemmas mult_1s:

      Numeral1 * a = a

      a * Numeral1 = a

      (-1::'a) * z = - z

      z * (-1::'a) = - z

### Special Arithmetic Rules for Abstract 0 and 1

lemma binop_eq:

      [| f x y = g x y; x = x'; y = y' |] ==> f x' y' = g x' y'

lemmas add_number_of_eq:

      number_of v1 + number_of w1 = number_of (bin_add v1 w1)

lemmas add_number_of_eq:

      number_of v1 + number_of w1 = number_of (bin_add v1 w1)

lemma one_add_one_is_two:

      (1::'a) + (1::'a) = (2::'a)

lemmas add_special:

      (1::'a) + (1::'a) = (2::'a)

      (1::'a) + number_of w = number_of (bin_add (Numeral.Pls BIT bit.B1) w)

      number_of v + (1::'a) = number_of (bin_add v (Numeral.Pls BIT bit.B1))

lemmas add_special:

      (1::'a) + (1::'a) = (2::'a)

      (1::'a) + number_of w = number_of (bin_add (Numeral.Pls BIT bit.B1) w)

      number_of v + (1::'a) = number_of (bin_add v (Numeral.Pls BIT bit.B1))

lemmas diff_special:

      (1::'a) - number_of w =
      number_of (bin_add (Numeral.Pls BIT bit.B1) (bin_minus w))

      number_of v - (1::'a) =
      number_of (bin_add v (bin_minus (Numeral.Pls BIT bit.B1)))

lemmas diff_special:

      (1::'a) - number_of w =
      number_of (bin_add (Numeral.Pls BIT bit.B1) (bin_minus w))

      number_of v - (1::'a) =
      number_of (bin_add v (bin_minus (Numeral.Pls BIT bit.B1)))

lemmas eq_special:

      ((0::'a) = number_of y) = iszero (number_of (bin_add Numeral.Pls (bin_minus y)))

      ((1::'a) = number_of y) =
      iszero (number_of (bin_add (Numeral.Pls BIT bit.B1) (bin_minus y)))

      (number_of x = (0::'a)) = iszero (number_of (bin_add x (bin_minus Numeral.Pls)))

      (number_of x = (1::'a)) =
      iszero (number_of (bin_add x (bin_minus (Numeral.Pls BIT bit.B1))))

lemmas eq_special:

      ((0::'a) = number_of y) = iszero (number_of (bin_add Numeral.Pls (bin_minus y)))

      ((1::'a) = number_of y) =
      iszero (number_of (bin_add (Numeral.Pls BIT bit.B1) (bin_minus y)))

      (number_of x = (0::'a)) = iszero (number_of (bin_add x (bin_minus Numeral.Pls)))

      (number_of x = (1::'a)) =
      iszero (number_of (bin_add x (bin_minus (Numeral.Pls BIT bit.B1))))

lemmas less_special:

      ((0::'a) < number_of y) = neg (number_of (bin_add Numeral.Pls (bin_minus y)))

      ((1::'a) < number_of y) =
      neg (number_of (bin_add (Numeral.Pls BIT bit.B1) (bin_minus y)))

      (number_of x < (0::'a)) = neg (number_of (bin_add x (bin_minus Numeral.Pls)))

      (number_of x < (1::'a)) =
      neg (number_of (bin_add x (bin_minus (Numeral.Pls BIT bit.B1))))

lemmas less_special:

      ((0::'a) < number_of y) = neg (number_of (bin_add Numeral.Pls (bin_minus y)))

      ((1::'a) < number_of y) =
      neg (number_of (bin_add (Numeral.Pls BIT bit.B1) (bin_minus y)))

      (number_of x < (0::'a)) = neg (number_of (bin_add x (bin_minus Numeral.Pls)))

      (number_of x < (1::'a)) =
      neg (number_of (bin_add x (bin_minus (Numeral.Pls BIT bit.B1))))

lemmas le_special:

      ((0::'a) ≤ number_of y) =
      (¬ neg (number_of (bin_add y (bin_minus Numeral.Pls))))

      ((1::'a) ≤ number_of y) =
      (¬ neg (number_of (bin_add y (bin_minus (Numeral.Pls BIT bit.B1)))))

      (number_of x ≤ (0::'a)) =
      (¬ neg (number_of (bin_add Numeral.Pls (bin_minus x))))

      (number_of x ≤ (1::'a)) =
      (¬ neg (number_of (bin_add (Numeral.Pls BIT bit.B1) (bin_minus x))))

lemmas le_special:

      ((0::'a) ≤ number_of y) =
      (¬ neg (number_of (bin_add y (bin_minus Numeral.Pls))))

      ((1::'a) ≤ number_of y) =
      (¬ neg (number_of (bin_add y (bin_minus (Numeral.Pls BIT bit.B1)))))

      (number_of x ≤ (0::'a)) =
      (¬ neg (number_of (bin_add Numeral.Pls (bin_minus x))))

      (number_of x ≤ (1::'a)) =
      (¬ neg (number_of (bin_add (Numeral.Pls BIT bit.B1) (bin_minus x))))

lemmas arith_special:

      (1::'a) + (1::'a) = (2::'a)

      (1::'a) + number_of w = number_of (bin_add (Numeral.Pls BIT bit.B1) w)

      number_of v + (1::'a) = number_of (bin_add v (Numeral.Pls BIT bit.B1))

      (1::'a) - number_of w =
      number_of (bin_add (Numeral.Pls BIT bit.B1) (bin_minus w))

      number_of v - (1::'a) =
      number_of (bin_add v (bin_minus (Numeral.Pls BIT bit.B1)))

      ((0::'a) = number_of y) = iszero (number_of (bin_add Numeral.Pls (bin_minus y)))

      ((1::'a) = number_of y) =
      iszero (number_of (bin_add (Numeral.Pls BIT bit.B1) (bin_minus y)))

      (number_of x = (0::'a)) = iszero (number_of (bin_add x (bin_minus Numeral.Pls)))

      (number_of x = (1::'a)) =
      iszero (number_of (bin_add x (bin_minus (Numeral.Pls BIT bit.B1))))

      ((0::'a) < number_of y) = neg (number_of (bin_add Numeral.Pls (bin_minus y)))

      ((1::'a) < number_of y) =
      neg (number_of (bin_add (Numeral.Pls BIT bit.B1) (bin_minus y)))

      (number_of x < (0::'a)) = neg (number_of (bin_add x (bin_minus Numeral.Pls)))

      (number_of x < (1::'a)) =
      neg (number_of (bin_add x (bin_minus (Numeral.Pls BIT bit.B1))))

      ((0::'a) ≤ number_of y) =
      (¬ neg (number_of (bin_add y (bin_minus Numeral.Pls))))

      ((1::'a) ≤ number_of y) =
      (¬ neg (number_of (bin_add y (bin_minus (Numeral.Pls BIT bit.B1)))))

      (number_of x ≤ (0::'a)) =
      (¬ neg (number_of (bin_add Numeral.Pls (bin_minus x))))

      (number_of x ≤ (1::'a)) =
      (¬ neg (number_of (bin_add (Numeral.Pls BIT bit.B1) (bin_minus x))))

lemmas arith_special:

      (1::'a) + (1::'a) = (2::'a)

      (1::'a) + number_of w = number_of (bin_add (Numeral.Pls BIT bit.B1) w)

      number_of v + (1::'a) = number_of (bin_add v (Numeral.Pls BIT bit.B1))

      (1::'a) - number_of w =
      number_of (bin_add (Numeral.Pls BIT bit.B1) (bin_minus w))

      number_of v - (1::'a) =
      number_of (bin_add v (bin_minus (Numeral.Pls BIT bit.B1)))

      ((0::'a) = number_of y) = iszero (number_of (bin_add Numeral.Pls (bin_minus y)))

      ((1::'a) = number_of y) =
      iszero (number_of (bin_add (Numeral.Pls BIT bit.B1) (bin_minus y)))

      (number_of x = (0::'a)) = iszero (number_of (bin_add x (bin_minus Numeral.Pls)))

      (number_of x = (1::'a)) =
      iszero (number_of (bin_add x (bin_minus (Numeral.Pls BIT bit.B1))))

      ((0::'a) < number_of y) = neg (number_of (bin_add Numeral.Pls (bin_minus y)))

      ((1::'a) < number_of y) =
      neg (number_of (bin_add (Numeral.Pls BIT bit.B1) (bin_minus y)))

      (number_of x < (0::'a)) = neg (number_of (bin_add x (bin_minus Numeral.Pls)))

      (number_of x < (1::'a)) =
      neg (number_of (bin_add x (bin_minus (Numeral.Pls BIT bit.B1))))

      ((0::'a) ≤ number_of y) =
      (¬ neg (number_of (bin_add y (bin_minus Numeral.Pls))))

      ((1::'a) ≤ number_of y) =
      (¬ neg (number_of (bin_add y (bin_minus (Numeral.Pls BIT bit.B1)))))

      (number_of x ≤ (0::'a)) =
      (¬ neg (number_of (bin_add Numeral.Pls (bin_minus x))))

      (number_of x ≤ (1::'a)) =
      (¬ neg (number_of (bin_add (Numeral.Pls BIT bit.B1) (bin_minus x))))

### Lemmas About Small Numerals

lemma of_int_m1:

      of_int -1 = (-1::'a)

lemma abs_minus_one:

      ¦-1::'a¦ = (1::'a)

lemma abs_power_minus_one:

      ¦(-1::'a) ^ n¦ = (1::'a)

lemma of_int_number_of_eq:

      of_int (number_of v) = number_of v

lemma mult_2:

      (2::'a) * z = z + z

lemma mult_2_right:

      z * (2::'a) = z + z

### More Inequality Reasoning

lemma zless_add1_eq:

      (w < z + 1) = (w < z ∨ w = z)

lemma add1_zle_eq:

      (w + 1 ≤ z) = (w < z)

lemma zle_diff1_eq:

      (w ≤ z - 1) = (w < z)

lemma zle_add1_eq_le:

      (w < z + 1) = (w ≤ z)

lemma int_one_le_iff_zero_less:

      (1 ≤ z) = (0 < z)

### The Functions @{term nat} and @{term int}

lemmas diff_int_def_symmetric:

      z1 + - w1 == z1 - w1

lemmas diff_int_def_symmetric:

      z1 + - w1 == z1 - w1

lemma nat_0:

      nat 0 = 0

lemma nat_1:

      nat 1 = Suc 0

lemma nat_2:

      nat 2 = Suc (Suc 0)

lemma one_less_nat_eq:

      (Suc 0 < nat z) = (1 < z)

lemmas int_eq_iff_number_of:

      (int m = number_of v) = (m = nat (number_of v) ∧ 0 ≤ number_of v)

lemmas int_eq_iff_number_of:

      (int m = number_of v) = (m = nat (number_of v) ∧ 0 ≤ number_of v)

lemma split_nat:

      P (nat i) = ((∀n. i = int n --> P n) ∧ (i < 0 --> P 0))

lemma zdiff_int:

      n ≤ m ==> int m - int n = int (m - n)

lemma nat_mult_distrib:

      0 ≤ z ==> nat (z * z') = nat z * nat z'

lemma nat_mult_distrib_neg:

      z ≤ 0 ==> nat (z * z') = nat (- z) * nat (- z')

lemma nat_abs_mult_distrib:

      nat ¦w * z¦ = nat ¦w¦ * nat ¦z¦

### Induction principles for int

theorem int_ge_induct:

      [| k ≤ i; P k; !!i. [| k ≤ i; P i |] ==> P (i + 1) |] ==> P i

theorem int_gr_induct:

      [| k < i; P (k + 1); !!i. [| k < i; P i |] ==> P (i + 1) |] ==> P i

theorem int_le_induct:

      [| i ≤ k; P k; !!i. [| i ≤ k; P i |] ==> P (i - 1) |] ==> P i

theorem int_less_induct:

      [| i < k; P (k - 1); !!i. [| i < k; P i |] ==> P (i - 1) |] ==> P i

### Intermediate value theorems

lemma int_val_lemma:

      (∀i<n. ¦f (i + 1) - f i¦ ≤ 1) --> f 0 ≤ k --> k ≤ f n --> (∃i≤n. f i = k)

lemmas nat0_intermed_int_val:

      [| ∀i<n. ¦f (i + 1) - f i¦ ≤ 1; f 0 ≤ k; k ≤ f n |] ==> ∃i≤n. f i = k

lemmas nat0_intermed_int_val:

      [| ∀i<n. ¦f (i + 1) - f i¦ ≤ 1; f 0 ≤ k; k ≤ f n |] ==> ∃i≤n. f i = k

lemma nat_intermed_int_val:

      [| ∀i. m ≤ i ∧ i < n --> ¦f (i + 1) - f i¦ ≤ 1; m < n; f m ≤ k; k ≤ f n |]
      ==> ∃i≥m. i ≤ n ∧ f i = k

### Products and 1, by T. M. Rasmussen

lemma zabs_less_one_iff:

      (¦z¦ < 1) = (z = 0)

lemma abs_zmult_eq_1:

      ¦m * n¦ = 1 ==> ¦m¦ = 1

lemma pos_zmult_eq_1_iff_lemma:

      m * n = 1 ==> m = 1 ∨ m = -1

lemma pos_zmult_eq_1_iff:

      0 < m ==> (m * n = 1) = (m = 1 ∧ n = 1)

lemma zmult_eq_1_iff:

      (m * n = 1) = (m = 1 ∧ n = 1 ∨ m = -1 ∧ n = -1)