Typeclasses for groups with an adjoined zero element

This file provides just the typeclass definitions, and the projection lemmas that expose their members.

Main definitions

• GroupWithZero
• CommGroupWithZero

class MulZeroClass (M₀ : Type u) extends Mul , Zero : Type u

• mul : M₀ → M₀ → M₀
• zero : M₀
• zero_mul : ∀ (a : M₀), 0 * a = 0

  Zero is a left absorbing element for multiplication

• mul_zero : ∀ (a : M₀), a * 0 = 0

  Zero is a right absorbing element for multiplication

Typeclass for expressing that a type M₀ with multiplication and a zero satisfies 0 * a = 0 and a * 0 = 0 for all a : M₀.

class IsLeftCancelMulZero (M₀ : Type u) [Mul M₀] [Zero M₀] : Prop

• mul_left_cancel_of_ne_zero : ∀ {a b c : M₀}, a ≠ 0 → a * b = a * c → b = c

  Multiplication by a nonzero element is left cancellative.

A mixin for left cancellative multiplication by nonzero elements.

theorem mul_left_cancel₀ {M₀ : Type u_1} [Mul M₀] [Zero M₀] [IsLeftCancelMulZero M₀] {a : M₀} {b : M₀} {c : M₀} (ha : a ≠ 0) (h : a * b = a * c) : b = c

theorem mul_right_injective₀ {M₀ : Type u_1} [Mul M₀] [Zero M₀] [IsLeftCancelMulZero M₀] {a : M₀} (ha : a ≠ 0) : Function.Injective ((fun x x_1 => x * x_1) a)

class IsRightCancelMulZero (M₀ : Type u) [Mul M₀] [Zero M₀] : Prop

• mul_right_cancel_of_ne_zero : ∀ {a b c : M₀}, b ≠ 0 → a * b = c * b → a = c

  Multiplicatin by a nonzero element is right cancellative.

A mixin for right cancellative multiplication by nonzero elements.

theorem mul_right_cancel₀ {M₀ : Type u_1} [Mul M₀] [Zero M₀] [IsRightCancelMulZero M₀] {a : M₀} {b : M₀} {c : M₀} (hb : b ≠ 0) (h : a * b = c * b) : a = c

theorem mul_left_injective₀ {M₀ : Type u_1} [Mul M₀] [Zero M₀] [IsRightCancelMulZero M₀] {b : M₀} (hb : b ≠ 0) : Function.Injective fun a => a * b

class IsCancelMulZero (M₀ : Type u) [Mul M₀] [Zero M₀] extends IsLeftCancelMulZero , IsRightCancelMulZero : Prop

A mixin for cancellative multiplication by nonzero elements.

class NoZeroDivisors (M₀ : Type u_4) [Mul M₀] [Zero M₀] : Prop

• eq_zero_or_eq_zero_of_mul_eq_zero : ∀ {a b : M₀}, a * b = 0 → a = 0 ∨ b = 0

  For all a and b of G₀, a * b = 0 implies a = 0 or b = 0.

Predicate typeclass for expressing that a * b = 0 implies a = 0 or b = 0 for all a and b of type G₀.

class SemigroupWithZero (S₀ : Type u) extends Semigroup , Zero : Type u

• mul : S₀ → S₀ → S₀
• mul_assoc : ∀ (a b c : S₀), a * b * c = a * (b * c)
• zero : S₀
• zero_mul : ∀ (a : S₀), 0 * a = 0

  Zero is a left absorbing element for multiplication

• mul_zero : ∀ (a : S₀), a * 0 = 0

  Zero is a right absorbing element for multiplication

A type S₀ is a "semigroup with zero” if it is a semigroup with zero element, and 0 is left and right absorbing.

class MulZeroOneClass (M₀ : Type u) extends MulOneClass , Zero : Type u

• one : M₀
• mul : M₀ → M₀ → M₀
• one_mul : ∀ (a : M₀), 1 * a = a
• mul_one : ∀ (a : M₀), a * 1 = a
• zero : M₀
• zero_mul : ∀ (a : M₀), 0 * a = 0

  Zero is a left absorbing element for multiplication

• mul_zero : ∀ (a : M₀), a * 0 = 0

  Zero is a right absorbing element for multiplication

A typeclass for non-associative monoids with zero elements.

class MonoidWithZero (M₀ : Type u) extends Monoid , Zero : Type u

• mul : M₀ → M₀ → M₀
• mul_assoc : ∀ (a b c : M₀), a * b * c = a * (b * c)
• one : M₀
• one_mul : ∀ (a : M₀), 1 * a = a
• mul_one : ∀ (a : M₀), a * 1 = a
• npow : ℕ → M₀ → M₀
• npow_zero : ∀ (x : M₀), Monoid.npow 0 x = 1
• npow_succ : ∀ (n : ℕ) (x : M₀), Monoid.npow (n + 1) x = x * Monoid.npow n x
• zero : M₀
• zero_mul : ∀ (a : M₀), 0 * a = 0

  Zero is a left absorbing element for multiplication

• mul_zero : ∀ (a : M₀), a * 0 = 0

  Zero is a right absorbing element for multiplication

A type M₀ is a “monoid with zero” if it is a monoid with zero element, and 0 is left and right absorbing.

class CancelMonoidWithZero (M₀ : Type u_4) extends MonoidWithZero , IsCancelMulZero : Type u_4

A type M is a CancelMonoidWithZero if it is a monoid with zero element, 0 is left and right absorbing, and left/right multiplication by a non-zero element is injective.

class CommMonoidWithZero (M₀ : Type u_4) extends CommMonoid , Zero : Type u_4

• mul : M₀ → M₀ → M₀
• mul_assoc : ∀ (a b c : M₀), a * b * c = a * (b * c)
• one : M₀
• one_mul : ∀ (a : M₀), 1 * a = a
• mul_one : ∀ (a : M₀), a * 1 = a
• npow : ℕ → M₀ → M₀
• npow_zero : ∀ (x : M₀), Monoid.npow 0 x = 1
• npow_succ : ∀ (n : ℕ) (x : M₀), Monoid.npow (n + 1) x = x * Monoid.npow n x
• mul_comm : ∀ (a b : M₀), a * b = b * a
• zero : M₀
• zero_mul : ∀ (a : M₀), 0 * a = 0

  Zero is a left absorbing element for multiplication

• mul_zero : ∀ (a : M₀), a * 0 = 0

  Zero is a right absorbing element for multiplication

A type M is a commutative “monoid with zero” if it is a commutative monoid with zero element, and 0 is left and right absorbing.

theorem mul_left_inj' {M₀ : Type u_1} [CancelMonoidWithZero M₀] {a : M₀} {b : M₀} {c : M₀} (hc : c ≠ 0) : a * c = b * c ↔ a = b

theorem mul_right_inj' {M₀ : Type u_1} [CancelMonoidWithZero M₀] {a : M₀} {b : M₀} {c : M₀} (ha : a ≠ 0) : a * b = a * c ↔ b = c

theorem IsLeftCancelMulZero.to_isRightCancelMulZero {M₀ : Type u_1} [CommSemigroup M₀] [Zero M₀] [IsLeftCancelMulZero M₀] : IsRightCancelMulZero M₀

theorem IsRightCancelMulZero.to_isLeftCancelMulZero {M₀ : Type u_1} [CommSemigroup M₀] [Zero M₀] [IsRightCancelMulZero M₀] : IsLeftCancelMulZero M₀

theorem IsLeftCancelMulZero.to_isCancelMulZero {M₀ : Type u_1} [CommSemigroup M₀] [Zero M₀] [IsLeftCancelMulZero M₀] : IsCancelMulZero M₀

theorem IsRightCancelMulZero.to_isCancelMulZero {M₀ : Type u_1} [CommSemigroup M₀] [Zero M₀] [IsRightCancelMulZero M₀] : IsCancelMulZero M₀

class CancelCommMonoidWithZero (M₀ : Type u_4) extends CommMonoidWithZero , IsLeftCancelMulZero : Type u_4

A type M is a CancelCommMonoidWithZero if it is a commutative monoid with zero element, 0 is left and right absorbing, and left/right multiplication by a non-zero element is injective.

instance CancelCommMonoidWithZero.toCancelMonoidWithZero {M₀ : Type u_1} [CancelCommMonoidWithZero M₀] : CancelMonoidWithZero M₀

class GroupWithZero (G₀ : Type u) extends MonoidWithZero , Inv , Div , Nontrivial : Type u

• mul : G₀ → G₀ → G₀
• mul_assoc : ∀ (a b c : G₀), a * b * c = a * (b * c)
• one : G₀
• one_mul : ∀ (a : G₀), 1 * a = a
• mul_one : ∀ (a : G₀), a * 1 = a
• npow : ℕ → G₀ → G₀
• npow_zero : ∀ (x : G₀), Monoid.npow 0 x = 1
• npow_succ : ∀ (n : ℕ) (x : G₀), Monoid.npow (n + 1) x = x * Monoid.npow n x
• zero : G₀
• zero_mul : ∀ (a : G₀), 0 * a = 0
• mul_zero : ∀ (a : G₀), a * 0 = 0
• inv : G₀ → G₀
• div : G₀ → G₀ → G₀
• div_eq_mul_inv : ∀ (a b : G₀), a / b = a * b⁻¹

  a / b := a * b⁻¹

• zpow : ℤ → G₀ → G₀

  The power operation: a ^ n = a * ··· * a; a ^ (-n) = a⁻¹ * ··· a⁻¹ (n times)

• zpow_zero' : ∀ (a : G₀), GroupWithZero.zpow 0 a = 1

  a ^ 0 = 1

• zpow_succ' : ∀ (n : ℕ) (a : G₀), GroupWithZero.zpow (Int.ofNat (Nat.succ n)) a = a * GroupWithZero.zpow (Int.ofNat n) a

  a ^ (n + 1) = a * a ^ n

• zpow_neg' : ∀ (n : ℕ) (a : G₀), GroupWithZero.zpow (Int.negSucc n) a = (GroupWithZero.zpow (↑(Nat.succ n)) a)⁻¹

  a ^ -(n + 1) = (a ^ (n + 1))⁻¹

• exists_pair_ne : ∃ x y, x ≠ y
• inv_zero : 0⁻¹ = 0

  The inverse of 0 in a group with zero is 0.

• mul_inv_cancel : ∀ (a : G₀), a ≠ 0 → a * a⁻¹ = 1

  Every nonzero element of a group with zero is invertible.

A type G₀ is a “group with zero” if it is a monoid with zero element (distinct from 1) such that every nonzero element is invertible. The type is required to come with an “inverse” function, and the inverse of 0 must be 0.

Examples include division rings and the ordered monoids that are the target of valuations in general valuation theory.

@[simp]

theorem mul_inv_cancel {G₀ : Type u} [GroupWithZero G₀] {a : G₀} (h : a ≠ 0) : a * a⁻¹ = 1

class CommGroupWithZero (G₀ : Type u_4) extends CommMonoidWithZero , Inv , Div , Nontrivial : Type u_4

• mul : G₀ → G₀ → G₀
• mul_assoc : ∀ (a b c : G₀), a * b * c = a * (b * c)
• one : G₀
• one_mul : ∀ (a : G₀), 1 * a = a
• mul_one : ∀ (a : G₀), a * 1 = a
• npow : ℕ → G₀ → G₀
• npow_zero : ∀ (x : G₀), Monoid.npow 0 x = 1
• npow_succ : ∀ (n : ℕ) (x : G₀), Monoid.npow (n + 1) x = x * Monoid.npow n x
• mul_comm : ∀ (a b : G₀), a * b = b * a
• zero : G₀
• zero_mul : ∀ (a : G₀), 0 * a = 0
• mul_zero : ∀ (a : G₀), a * 0 = 0
• inv : G₀ → G₀
• div : G₀ → G₀ → G₀
• div_eq_mul_inv : ∀ (a b : G₀), a / b = a * b⁻¹

  a / b := a * b⁻¹

• zpow : ℤ → G₀ → G₀

  The power operation: a ^ n = a * ··· * a; a ^ (-n) = a⁻¹ * ··· a⁻¹ (n times)

• zpow_zero' : ∀ (a : G₀), CommGroupWithZero.zpow 0 a = 1

  a ^ 0 = 1

• zpow_succ' : ∀ (n : ℕ) (a : G₀), CommGroupWithZero.zpow (Int.ofNat (Nat.succ n)) a = a * CommGroupWithZero.zpow (Int.ofNat n) a

  a ^ (n + 1) = a * a ^ n

• zpow_neg' : ∀ (n : ℕ) (a : G₀), CommGroupWithZero.zpow (Int.negSucc n) a = (CommGroupWithZero.zpow (↑(Nat.succ n)) a)⁻¹

  a ^ -(n + 1) = (a ^ (n + 1))⁻¹

• exists_pair_ne : ∃ x y, x ≠ y
• inv_zero : 0⁻¹ = 0

  The inverse of 0 in a group with zero is 0.

• mul_inv_cancel : ∀ (a : G₀), a ≠ 0 → a * a⁻¹ = 1

  Every nonzero element of a group with zero is invertible.

A type G₀ is a commutative “group with zero” if it is a commutative monoid with zero element (distinct from 1) such that every nonzero element is invertible. The type is required to come with an “inverse” function, and the inverse of 0 must be 0.

@[simp]

theorem mul_inv_cancel_right₀ {G₀ : Type u} [GroupWithZero G₀] {b : G₀} (h : b ≠ 0) (a : G₀) : a * b * b⁻¹ = a

@[simp]

theorem mul_inv_cancel_left₀ {G₀ : Type u} [GroupWithZero G₀] {a : G₀} (h : a ≠ 0) (b : G₀) : a * (a⁻¹ * b) = b

theorem mul_eq_zero_of_left {M₀ : Type u_1} [MulZeroClass M₀] {a : M₀} (h : a = 0) (b : M₀) : a * b = 0

theorem mul_eq_zero_of_right {M₀ : Type u_1} [MulZeroClass M₀] (a : M₀) {b : M₀} (h : b = 0) : a * b = 0

@[simp]

theorem mul_eq_zero {M₀ : Type u_1} [MulZeroClass M₀] [NoZeroDivisors M₀] {a : M₀} {b : M₀} : a * b = 0 ↔ a = 0 ∨ b = 0

If α has no zero divisors, then the product of two elements equals zero iff one of them equals zero.

@[simp]

theorem zero_eq_mul {M₀ : Type u_1} [MulZeroClass M₀] [NoZeroDivisors M₀] {a : M₀} {b : M₀} : 0 = a * b ↔ a = 0 ∨ b = 0

If α has no zero divisors, then the product of two elements equals zero iff one of them equals zero.

theorem mul_ne_zero_iff {M₀ : Type u_1} [MulZeroClass M₀] [NoZeroDivisors M₀] {a : M₀} {b : M₀} : a * b ≠ 0 ↔ a ≠ 0 ∧ b ≠ 0

If α has no zero divisors, then the product of two elements is nonzero iff both of them are nonzero.

theorem mul_eq_zero_comm {M₀ : Type u_1} [MulZeroClass M₀] [NoZeroDivisors M₀] {a : M₀} {b : M₀} : a * b = 0 ↔ b * a = 0

If α has no zero divisors, then for elements a, b : α, a * b equals zero iff so is b * a.

theorem mul_ne_zero_comm {M₀ : Type u_1} [MulZeroClass M₀] [NoZeroDivisors M₀] {a : M₀} {b : M₀} : a * b ≠ 0 ↔ b * a ≠ 0

If α has no zero divisors, then for elements a, b : α, a * b is nonzero iff so is b * a.

theorem mul_self_eq_zero {M₀ : Type u_1} [MulZeroClass M₀] [NoZeroDivisors M₀] {a : M₀} : a * a = 0 ↔ a = 0

theorem zero_eq_mul_self {M₀ : Type u_1} [MulZeroClass M₀] [NoZeroDivisors M₀] {a : M₀} : 0 = a * a ↔ a = 0

theorem mul_self_ne_zero {M₀ : Type u_1} [MulZeroClass M₀] [NoZeroDivisors M₀] {a : M₀} : a * a ≠ 0 ↔ a ≠ 0

theorem zero_ne_mul_self {M₀ : Type u_1} [MulZeroClass M₀] [NoZeroDivisors M₀] {a : M₀} : 0 ≠ a * a ↔ a ≠ 0