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def Int.«term-[_+1]» : Lean.ParserDescr

-[n+1] is suggestive notation for negSucc n, which is the second constructor of Int for making strictly negative numbers by mapping n : Nat to -(n + 1).

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def Int.sign : Int → Int

Returns the "sign" of the integer as another integer: 1 for positive numbers, -1 for negative numbers, and 0 for 0.

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• Int.sign x = match x with | Int.ofNat (Nat.succ n) => 1 | Int.ofNat 0 => 0 | Int.negSucc a => -1

toNat'

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def Int.toNat' : Int → Option Nat

• If n : Nat, then int.toNat' n = some n
• If n : Int is negative, then int.toNat' n = none.

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• Int.toNat' x = match x with | Int.ofNat n => some n | Int.negSucc a => none

Quotient and remainder

There are three main conventions for integer division, referred here as the E, F, T rounding conventions. All three pairs satisfy the identity x % y + (x / y) * y = x unconditionally, and satisfy x / 0 = 0 and x % 0 = x.

E-rounding division

This pair satisfies 0 ≤ mod x y < natAbs y≤ mod x y < natAbs y for y ≠ 0≠ 0.

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def Int.ediv : Int → Int → Int

Integer division. This version of Int.div uses the E-rounding convention (euclidean division), in which Int.emod x y satisfies 0 ≤ mod x y < natAbs y≤ mod x y < natAbs y for y ≠ 0≠ 0 and Int.ediv is the unique function satisfying emod x y + (ediv x y) * y = x.

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def Int.emod : Int → Int → Int

Integer modulus. This version of Int.mod uses the E-rounding convention (euclidean division), in which Int.emod x y satisfies 0 ≤ emod x y < natAbs y≤ emod x y < natAbs y for y ≠ 0≠ 0 and Int.ediv is the unique function satisfying emod x y + (ediv x y) * y = x.

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• Int.emod x x = match x, x with | Int.ofNat m, n => Int.ofNat (m % Int.natAbs n) | Int.negSucc m, n => Int.subNatNat (Int.natAbs n) (Nat.succ (m % Int.natAbs n))

F-rounding division

This pair satisfies fdiv x y = floor (x / y).

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def Int.fdiv : Int → Int → Int

Integer division. This version of Int.div uses the F-rounding convention (flooring division), in which Int.fdiv x y satisfies fdiv x y = floor (x / y) and Int.fmod is the unique function satisfying fmod x y + (fdiv x y) * y = x.

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def Int.fmod : Int → Int → Int

Integer modulus. This version of Int.mod uses the F-rounding convention (flooring division), in which Int.fdiv x y satisfies fdiv x y = floor (x / y) and Int.fmod is the unique function satisfying fmod x y + (fdiv x y) * y = x.

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T-rounding division

This pair satisfies div x y = round_to_zero (x / y). Int.div and Int.mod are defined in core lean.

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instance Int.instDivInt_1 : Div Int

Core Lean provides instances using T-rounding division, i.e. Int.div and Int.mod. We override these here.

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• Int.instDivInt_1 = { div := Int.ediv }

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instance Int.instModInt_1 : Mod Int

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• Int.instModInt_1 = { mod := Int.emod }

gcd

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def Int.gcd (m : Int) (n : Int) : Nat

Computes the greatest common divisor of two integers, as a Nat.

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• Int.gcd m n = Nat.gcd (Int.natAbs m) (Int.natAbs n)

divisibility

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instance Int.instDvdInt : Dvd Int

Divisibility of integers. a ∣ b∣ b (typed as \|) says that there is some c such that b = a * c.

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• Int.instDvdInt = { dvd := fun a b => ∃ c, b = a * c }