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

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

• 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

@[simp]

theorem MulZeroClass.zero_mul {M₀ : Type u} [self : MulZeroClass M₀] (a : M₀) : 0 * a = 0

Zero is a left absorbing element for multiplication

@[simp]

theorem MulZeroClass.mul_zero {M₀ : Type u} [self : MulZeroClass M₀] (a : M₀) : a * 0 = 0

Zero is a right absorbing element for multiplication

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

A mixin for left cancellative multiplication by nonzero elements.

• 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.

theorem IsLeftCancelMulZero.mul_left_cancel_of_ne_zero {M₀ : Type u} : ∀ {inst : Mul M₀} {inst_1 : Zero M₀} [self : IsLeftCancelMulZero M₀] {a b c : M₀}, a ≠ 0 → a * b = a * c → b = c

Multiplication by a nonzero element is left cancellative.

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 : M₀) => a * x

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

A mixin for right cancellative multiplication by nonzero elements.

• 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.

theorem IsRightCancelMulZero.mul_right_cancel_of_ne_zero {M₀ : Type u} : ∀ {inst : Mul M₀} {inst_1 : Zero M₀} [self : IsRightCancelMulZero M₀] {a b c : M₀}, b ≠ 0 → a * b = c * b → a = c

Multiplicatin by a nonzero element is right cancellative.

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 : M₀) => 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_2) [Mul M₀] [Zero M₀] : Prop

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

• 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.

theorem NoZeroDivisors.eq_zero_or_eq_zero_of_mul_eq_zero {M₀ : Type u_2} : ∀ {inst : Mul M₀} {inst_1 : Zero M₀} [self : NoZeroDivisors M₀] {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.

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

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 , MulZeroClass , One , Mul , Zero : Type u

A typeclass for non-associative monoids with zero elements.

class MonoidWithZero (M₀ : Type u) extends Monoid , MulZeroOneClass , SemigroupWithZero , Semigroup , MulOneClass , MulZeroClass , One , Mul , Zero : Type u

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_2) extends MonoidWithZero , IsCancelMulZero , Monoid , MulZeroOneClass , SemigroupWithZero , Semigroup , MulOneClass , MulZeroClass , One , Mul , Zero , IsLeftCancelMulZero , IsRightCancelMulZero : Type u_2

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_2) extends CommMonoid , MonoidWithZero , Monoid , CommSemigroup , MulZeroOneClass , SemigroupWithZero , Semigroup , MulOneClass , MulZeroClass , One , CommMagma , Mul , Zero : Type u_2

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_2) extends CommMonoidWithZero , IsLeftCancelMulZero , CommMonoid , MonoidWithZero , Monoid , CommSemigroup , MulZeroOneClass , SemigroupWithZero , Semigroup , MulOneClass , MulZeroClass , One , CommMagma , Mul , Zero : Type u_2

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 100]

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

Equations

• CancelCommMonoidWithZero.toCancelMonoidWithZero = CancelMonoidWithZero.mk

class MulDivCancelClass (M₀ : Type u_2) [MonoidWithZero M₀] [Div M₀] : Prop

Prop-valued mixin for a monoid with zero to be equipped with a cancelling division.

The obvious use case is groups with zero, but this condition is also satisfied by ℕ, ℤ and, more generally, any euclidean domain.

• mul_div_cancel : ∀ (a b : M₀), b ≠ 0 → a * b / b = a

theorem MulDivCancelClass.mul_div_cancel {M₀ : Type u_2} : ∀ {inst : MonoidWithZero M₀} {inst_1 : Div M₀} [self : MulDivCancelClass M₀] (a b : M₀), b ≠ 0 → a * b / b = a

@[simp]

theorem mul_div_cancel_right₀ {M₀ : Type u_1} [MonoidWithZero M₀] [Div M₀] [MulDivCancelClass M₀] (a : M₀) {b : M₀} (hb : b ≠ 0) : a * b / b = a

@[simp]

theorem mul_div_cancel_left₀ {M₀ : Type u_1} [CommMonoidWithZero M₀] [Div M₀] [MulDivCancelClass M₀] (b : M₀) {a : M₀} (ha : a ≠ 0) : a * b / a = b

class GroupWithZero (G₀ : Type u) extends MonoidWithZero , DivInvMonoid , Nontrivial , Monoid , MulZeroOneClass , SemigroupWithZero , Inv , Div , Semigroup , MulOneClass , MulZeroClass , One , Mul , Zero : Type u

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.

theorem GroupWithZero.inv_zero {G₀ : Type u} [self : GroupWithZero G₀] : 0⁻¹ = 0

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

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

Every nonzero element of a group with zero is invertible.

@[simp]

theorem inv_zero {G₀ : Type u} [GroupWithZero G₀] : 0⁻¹ = 0

@[simp]

theorem mul_inv_cancel₀ {G₀ : Type u} [GroupWithZero G₀] {a : G₀} (h : a ≠ 0) : a * a⁻¹ = 1

@[instance 100]

instance GroupWithZero.toMulDivCancelClass {G₀ : Type u} [GroupWithZero G₀] : MulDivCancelClass G₀

Equations

• ⋯ = ⋯

class CommGroupWithZero (G₀ : Type u_2) extends CommMonoidWithZero , GroupWithZero , CommMonoid , MonoidWithZero , DivInvMonoid , Nontrivial , Monoid , CommSemigroup , MulZeroOneClass , SemigroupWithZero , Inv , Div , Semigroup , MulOneClass , MulZeroClass , One , CommMagma , Mul , Zero : Type u_2

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.

theorem eq_zero_or_one_of_sq_eq_self {M₀ : Type u_1} [CancelMonoidWithZero M₀] {x : M₀} (hx : x ^ 2 = x) : x = 0 ∨ x = 1

@[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