mathlib documentation

algebra.group.defs

Typeclasses for (semi)groups and monoid

In this file we define typeclasses for algebraic structures with one binary operation. The classes are named (add_)?(comm_)?(semigroup|monoid|group), where add_ means that the class uses additive notation and comm_ means that the class assumes that the binary operation is commutative.

The file does not contain any lemmas except for

For basic lemmas about these classes see algebra.group.basic.

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def left_mul {G : Type u} [has_mul G] :
G → G → G

left_mul g denotes left multiplication by g

Equations
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def left_add {G : Type u} [has_add G] :
G → G → G

left_add g denotes left addition by g

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def right_add {G : Type u} [has_add G] :
G → G → G

right_add g denotes right addition by g

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def right_mul {G : Type u} [has_mul G] :
G → G → G

right_mul g denotes right multiplication by g

Equations
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@[instance]
def semigroup.to_has_mul (G : Type u) [s : semigroup G] :
has_mul G

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@[class]
structure semigroup (G : Type u) :
Type u
  • mul : G → G → G
  • mul_assoc : ∀ (a b c_1 : G), (a * b) * c_1 = a * b * c_1

A semigroup is a type with an associative (*).

Instances
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@[instance]
def add_semigroup.to_has_add (G : Type u) [s : add_semigroup G] :
has_add G

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@[class]
structure add_semigroup (G : Type u) :
Type u
  • add : G → G → G
  • add_assoc : ∀ (a b c_1 : G), a + b + c_1 = a + (b + c_1)

An additive semigroup is a type with an associative (+).

Instances
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theorem add_assoc {G : Type u} [add_semigroup G] (a b c : G) :
a + b + c = a + (b + c)

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theorem mul_assoc {G : Type u} [semigroup G] (a b c : G) :
(a * b) * c = a * b * c

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@[instance]
def add_semigroup.to_is_associative {G : Type u} [add_semigroup G] :
is_associative G has_add.add

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@[instance]
def semigroup.to_is_associative {G : Type u} [semigroup G] :
is_associative G has_mul.mul

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@[class]
structure comm_semigroup (G : Type u) :
Type u
  • mul : G → G → G
  • mul_assoc : ∀ (a b c_1 : G), (a * b) * c_1 = a * b * c_1
  • mul_comm : ∀ (a b : G), a * b = b * a

A commutative semigroup is a type with an associative commutative (*).

Instances
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@[instance]
def comm_semigroup.to_semigroup (G : Type u) [s : comm_semigroup G] :
semigroup G

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@[instance]
def add_comm_semigroup.to_add_semigroup (G : Type u) [s : add_comm_semigroup G] :
add_semigroup G

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@[class]
structure add_comm_semigroup (G : Type u) :
Type u
  • add : G → G → G
  • add_assoc : ∀ (a b c_1 : G), a + b + c_1 = a + (b + c_1)
  • add_comm : ∀ (a b : G), a + b = b + a

A commutative additive semigroup is a type with an associative commutative (+).

Instances
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theorem add_comm {G : Type u} [add_comm_semigroup G] (a b : G) :
a + b = b + a

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theorem mul_comm {G : Type u} [comm_semigroup G] (a b : G) :
a * b = b * a

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@[instance]
def comm_semigroup.to_is_commutative {G : Type u} [comm_semigroup G] :
is_commutative G has_mul.mul

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@[instance]
def add_comm_semigroup.to_is_commutative {G : Type u} [add_comm_semigroup G] :
is_commutative G has_add.add

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@[instance]
def left_cancel_semigroup.to_semigroup (G : Type u) [s : left_cancel_semigroup G] :
semigroup G

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@[class]
structure left_cancel_semigroup (G : Type u) :
Type u
  • mul : G → G → G
  • mul_assoc : ∀ (a b c_1 : G), (a * b) * c_1 = a * b * c_1
  • mul_left_cancel : ∀ (a b c_1 : G), a * b = a * c_1 → b = c_1

A left_cancel_semigroup is a semigroup such that a * b = a * c implies b = c.

Instances
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@[class]
structure add_left_cancel_semigroup (G : Type u) :
Type u
  • add : G → G → G
  • add_assoc : ∀ (a b c_1 : G), a + b + c_1 = a + (b + c_1)
  • add_left_cancel : ∀ (a b c_1 : G), a + b = a + c_1 → b = c_1

An add_left_cancel_semigroup is an additive semigroup such that a + b = a + c implies b = c.

Instances
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@[instance]
def add_left_cancel_semigroup.to_add_semigroup (G : Type u) [s : add_left_cancel_semigroup G] :
add_semigroup G

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theorem mul_left_cancel {G : Type u} [left_cancel_semigroup G] {a b c : G} :
a * b = a * c → b = c

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theorem add_left_cancel {G : Type u} [add_left_cancel_semigroup G] {a b c : G} :
a + b = a + c → b = c

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theorem add_left_cancel_iff {G : Type u} [add_left_cancel_semigroup G] {a b c : G} :
a + b = a + c ↔ b = c

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theorem mul_left_cancel_iff {G : Type u} [left_cancel_semigroup G] {a b c : G} :
a * b = a * c ↔ b = c

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theorem add_right_injective {G : Type u} [add_left_cancel_semigroup G] (a : G) :
function.injective (has_add.add a)

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theorem mul_right_injective {G : Type u} [left_cancel_semigroup G] (a : G) :
function.injective (has_mul.mul a)

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@[simp]
theorem mul_right_inj {G : Type u} [left_cancel_semigroup G] (a : G) {b c : G} :
a * b = a * c ↔ b = c

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@[simp]
theorem add_right_inj {G : Type u} [add_left_cancel_semigroup G] (a : G) {b c : G} :
a + b = a + c ↔ b = c

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@[class]
structure right_cancel_semigroup (G : Type u) :
Type u
  • mul : G → G → G
  • mul_assoc : ∀ (a b c_1 : G), (a * b) * c_1 = a * b * c_1
  • mul_right_cancel : ∀ (a b c_1 : G), a * b = c_1 * b → a = c_1

A right_cancel_semigroup is a semigroup such that a * b = c * b implies a = c.

Instances
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@[instance]
def right_cancel_semigroup.to_semigroup (G : Type u) [s : right_cancel_semigroup G] :
semigroup G

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@[class]
structure add_right_cancel_semigroup (G : Type u) :
Type u
  • add : G → G → G
  • add_assoc : ∀ (a b c_1 : G), a + b + c_1 = a + (b + c_1)
  • add_right_cancel : ∀ (a b c_1 : G), a + b = c_1 + b → a = c_1

An add_right_cancel_semigroup is an additive semigroup such that a + b = c + b implies a = c.

Instances
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@[instance]
def add_right_cancel_semigroup.to_add_semigroup (G : Type u) [s : add_right_cancel_semigroup G] :
add_semigroup G

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theorem mul_right_cancel {G : Type u} [right_cancel_semigroup G] {a b c : G} :
a * b = c * b → a = c

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theorem add_right_cancel {G : Type u} [add_right_cancel_semigroup G] {a b c : G} :
a + b = c + b → a = c

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theorem mul_right_cancel_iff {G : Type u} [right_cancel_semigroup G] {a b c : G} :
b * a = c * a ↔ b = c

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theorem add_right_cancel_iff {G : Type u} [add_right_cancel_semigroup G] {a b c : G} :
b + a = c + a ↔ b = c

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theorem add_left_injective {G : Type u} [add_right_cancel_semigroup G] (a : G) :
function.injective (λ (x : G), x + a)

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theorem mul_left_injective {G : Type u} [right_cancel_semigroup G] (a : G) :
function.injective (λ (x : G), x * a)

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@[simp]
theorem add_left_inj {G : Type u} [add_right_cancel_semigroup G] (a : G) {b c : G} :
b + a = c + a ↔ b = c

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@[simp]
theorem mul_left_inj {G : Type u} [right_cancel_semigroup G] (a : G) {b c : G} :
b * a = c * a ↔ b = c

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@[instance]
def monoid.to_has_one (M : Type u) [s : monoid M] :
has_one M

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@[instance]
def monoid.to_semigroup (M : Type u) [s : monoid M] :
semigroup M

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@[class]
structure monoid (M : Type u) :
Type u
  • mul : M → M → M
  • mul_assoc : ∀ (a b c_1 : M), (a * b) * c_1 = a * b * c_1
  • one : M
  • one_mul : ∀ (a : M), 1 * a = a
  • mul_one : ∀ (a : M), a * 1 = a

A monoid is a semigroup with an element 1 such that 1 * a = a * 1 = a.

Instances
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@[instance]
def add_monoid.to_add_semigroup (M : Type u) [s : add_monoid M] :
add_semigroup M

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@[instance]
def add_monoid.to_has_zero (M : Type u) [s : add_monoid M] :
has_zero M

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@[class]
structure add_monoid (M : Type u) :
Type u
  • add : M → M → M
  • add_assoc : ∀ (a b c_1 : M), a + b + c_1 = a + (b + c_1)
  • zero : M
  • zero_add : ∀ (a : M), 0 + a = a
  • add_zero : ∀ (a : M), a + 0 = a

An add_monoid is an add_semigroup with an element 0 such that 0 + a = a + 0 = a.

Instances
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@[simp]
theorem one_mul {M : Type u} [monoid M] (a : M) :
1 * a = a

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@[simp]
theorem zero_add {M : Type u} [add_monoid M] (a : M) :
0 + a = a

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@[simp]
theorem add_zero {M : Type u} [add_monoid M] (a : M) :
a + 0 = a

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@[simp]
theorem mul_one {M : Type u} [monoid M] (a : M) :
a * 1 = a

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@[instance]
def monoid_to_is_left_id {M : Type u} [monoid M] :
is_left_id M has_mul.mul 1

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@[instance]
def add_monoid_to_is_left_id {M : Type u} [add_monoid M] :
is_left_id M has_add.add 0

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@[instance]
def add_monoid_to_is_right_id {M : Type u} [add_monoid M] :
is_right_id M has_add.add 0

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@[instance]
def monoid_to_is_right_id {M : Type u} [monoid M] :
is_right_id M has_mul.mul 1

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theorem left_inv_eq_right_inv {M : Type u} [monoid M] {a b c : M} (hba : b * a = 1) (hac : a * c = 1) :
b = c

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theorem left_neg_eq_right_neg {M : Type u} [add_monoid M] {a b c : M} (hba : b + a = 0) (hac : a + c = 0) :
b = c

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@[instance]
def comm_monoid.to_comm_semigroup (M : Type u) [s : comm_monoid M] :
comm_semigroup M

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@[class]
structure comm_monoid (M : Type u) :
Type u
  • mul : M → M → M
  • mul_assoc : ∀ (a b c_1 : M), (a * b) * c_1 = a * b * c_1
  • one : M
  • one_mul : ∀ (a : M), 1 * a = a
  • mul_one : ∀ (a : M), a * 1 = a
  • mul_comm : ∀ (a b : M), a * b = b * a

A commutative monoid is a monoid with commutative (*).

Instances
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@[instance]
def comm_monoid.to_monoid (M : Type u) [s : comm_monoid M] :
monoid M

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@[instance]
def add_comm_monoid.to_add_monoid (M : Type u) [s : add_comm_monoid M] :
add_monoid M

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@[class]
structure add_comm_monoid (M : Type u) :
Type u
  • add : M → M → M
  • add_assoc : ∀ (a b c_1 : M), a + b + c_1 = a + (b + c_1)
  • zero : M
  • zero_add : ∀ (a : M), 0 + a = a
  • add_zero : ∀ (a : M), a + 0 = a
  • add_comm : ∀ (a b : M), a + b = b + a

An additive commutative monoid is an additive monoid with commutative (+).

Instances
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@[instance]
def add_comm_monoid.to_add_comm_semigroup (M : Type u) [s : add_comm_monoid M] :
add_comm_semigroup M

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@[instance]
def add_left_cancel_monoid.to_add_monoid (M : Type u) [s : add_left_cancel_monoid M] :
add_monoid M

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@[class]
structure add_left_cancel_monoid (M : Type u) :
Type u
  • add : M → M → M
  • add_assoc : ∀ (a b c_1 : M), a + b + c_1 = a + (b + c_1)
  • add_left_cancel : ∀ (a b c_1 : M), a + b = a + c_1 → b = c_1
  • zero : M
  • zero_add : ∀ (a : M), 0 + a = a
  • add_zero : ∀ (a : M), a + 0 = a

An additive monoid in which addition is left-cancellative. Main examples are ℕ and groups. This is the right typeclass for many sum lemmas, as having a zero is useful to define the sum over the empty set, so add_left_cancel_semigroup is not enough.

Instances
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@[instance]
def add_left_cancel_monoid.to_add_left_cancel_semigroup (M : Type u) [s : add_left_cancel_monoid M] :
add_left_cancel_semigroup M

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@[class]
structure left_cancel_monoid (M : Type u) :
Type u
  • mul : M → M → M
  • mul_assoc : ∀ (a b c_1 : M), (a * b) * c_1 = a * b * c_1
  • mul_left_cancel : ∀ (a b c_1 : M), a * b = a * c_1 → b = c_1
  • one : M
  • one_mul : ∀ (a : M), 1 * a = a
  • mul_one : ∀ (a : M), a * 1 = a

A monoid in which multiplication is left-cancellative.

Instances
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@[instance]
def left_cancel_monoid.to_left_cancel_semigroup (M : Type u) [s : left_cancel_monoid M] :
left_cancel_semigroup M

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@[instance]
def left_cancel_monoid.to_monoid (M : Type u) [s : left_cancel_monoid M] :
monoid M

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@[instance]
def add_left_cancel_comm_monoid.to_add_left_cancel_monoid (M : Type u) [s : add_left_cancel_comm_monoid M] :
add_left_cancel_monoid M

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@[instance]
def add_left_cancel_comm_monoid.to_add_comm_monoid (M : Type u) [s : add_left_cancel_comm_monoid M] :
add_comm_monoid M

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@[class]
structure add_left_cancel_comm_monoid (M : Type u) :
Type u
  • add : M → M → M
  • add_assoc : ∀ (a b c_1 : M), a + b + c_1 = a + (b + c_1)
  • add_left_cancel : ∀ (a b c_1 : M), a + b = a + c_1 → b = c_1
  • zero : M
  • zero_add : ∀ (a : M), 0 + a = a
  • add_zero : ∀ (a : M), a + 0 = a
  • add_comm : ∀ (a b : M), a + b = b + a

Commutative version of add_left_cancel_monoid.

Instances
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@[instance]
def left_cancel_comm_monoid.to_left_cancel_monoid (M : Type u) [s : left_cancel_comm_monoid M] :
left_cancel_monoid M

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@[class]
structure left_cancel_comm_monoid (M : Type u) :
Type u
  • mul : M → M → M
  • mul_assoc : ∀ (a b c_1 : M), (a * b) * c_1 = a * b * c_1
  • mul_left_cancel : ∀ (a b c_1 : M), a * b = a * c_1 → b = c_1
  • one : M
  • one_mul : ∀ (a : M), 1 * a = a
  • mul_one : ∀ (a : M), a * 1 = a
  • mul_comm : ∀ (a b : M), a * b = b * a

Commutative version of left_cancel_monoid.

Instances
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@[instance]
def left_cancel_comm_monoid.to_comm_monoid (M : Type u) [s : left_cancel_comm_monoid M] :
comm_monoid M

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@[instance]
def add_right_cancel_monoid.to_add_right_cancel_semigroup (M : Type u) [s : add_right_cancel_monoid M] :
add_right_cancel_semigroup M

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@[class]
structure add_right_cancel_monoid (M : Type u) :
Type u
  • add : M → M → M
  • add_assoc : ∀ (a b c_1 : M), a + b + c_1 = a + (b + c_1)
  • add_right_cancel : ∀ (a b c_1 : M), a + b = c_1 + b → a = c_1
  • zero : M
  • zero_add : ∀ (a : M), 0 + a = a
  • add_zero : ∀ (a : M), a + 0 = a

An additive monoid in which addition is right-cancellative. Main examples are ℕ and groups. This is the right typeclass for many sum lemmas, as having a zero is useful to define the sum over the empty set, so add_right_cancel_semigroup is not enough.

Instances
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@[instance]
def add_right_cancel_monoid.to_add_monoid (M : Type u) [s : add_right_cancel_monoid M] :
add_monoid M

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@[instance]
def right_cancel_monoid.to_monoid (M : Type u) [s : right_cancel_monoid M] :
monoid M

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@[class]
structure right_cancel_monoid (M : Type u) :
Type u
  • mul : M → M → M
  • mul_assoc : ∀ (a b c_1 : M), (a * b) * c_1 = a * b * c_1
  • mul_right_cancel : ∀ (a b c_1 : M), a * b = c_1 * b → a = c_1
  • one : M
  • one_mul : ∀ (a : M), 1 * a = a
  • mul_one : ∀ (a : M), a * 1 = a

A monoid in which multiplication is right-cancellative.

Instances
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@[instance]
def right_cancel_monoid.to_right_cancel_semigroup (M : Type u) [s : right_cancel_monoid M] :
right_cancel_semigroup M

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@[class]
structure add_right_cancel_comm_monoid (M : Type u) :
Type u
  • add : M → M → M
  • add_assoc : ∀ (a b c_1 : M), a + b + c_1 = a + (b + c_1)
  • add_right_cancel : ∀ (a b c_1 : M), a + b = c_1 + b → a = c_1
  • zero : M
  • zero_add : ∀ (a : M), 0 + a = a
  • add_zero : ∀ (a : M), a + 0 = a
  • add_comm : ∀ (a b : M), a + b = b + a

Commutative version of add_right_cancel_monoid.

Instances
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@[instance]
def add_right_cancel_comm_monoid.to_add_comm_monoid (M : Type u) [s : add_right_cancel_comm_monoid M] :
add_comm_monoid M

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@[instance]
def add_right_cancel_comm_monoid.to_add_right_cancel_monoid (M : Type u) [s : add_right_cancel_comm_monoid M] :
add_right_cancel_monoid M

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@[instance]
def right_cancel_comm_monoid.to_right_cancel_monoid (M : Type u) [s : right_cancel_comm_monoid M] :
right_cancel_monoid M

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@[instance]
def right_cancel_comm_monoid.to_comm_monoid (M : Type u) [s : right_cancel_comm_monoid M] :
comm_monoid M

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@[class]
structure right_cancel_comm_monoid (M : Type u) :
Type u
  • mul : M → M → M
  • mul_assoc : ∀ (a b c_1 : M), (a * b) * c_1 = a * b * c_1
  • mul_right_cancel : ∀ (a b c_1 : M), a * b = c_1 * b → a = c_1
  • one : M
  • one_mul : ∀ (a : M), 1 * a = a
  • mul_one : ∀ (a : M), a * 1 = a
  • mul_comm : ∀ (a b : M), a * b = b * a

Commutative version of right_cancel_monoid.

Instances
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@[instance]
def add_cancel_monoid.to_add_right_cancel_monoid (M : Type u) [s : add_cancel_monoid M] :
add_right_cancel_monoid M

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@[class]
structure add_cancel_monoid (M : Type u) :
Type u
  • add : M → M → M
  • add_assoc : ∀ (a b c_1 : M), a + b + c_1 = a + (b + c_1)
  • add_left_cancel : ∀ (a b c_1 : M), a + b = a + c_1 → b = c_1
  • zero : M
  • zero_add : ∀ (a : M), 0 + a = a
  • add_zero : ∀ (a : M), a + 0 = a
  • add_right_cancel : ∀ (a b c_1 : M), a + b = c_1 + b → a = c_1

An additive monoid in which addition is cancellative on both sides. Main examples are ℕ and groups. This is the right typeclass for many sum lemmas, as having a zero is useful to define the sum over the empty set, so add_right_cancel_semigroup is not enough.

Instances
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@[instance]
def add_cancel_monoid.to_add_left_cancel_monoid (M : Type u) [s : add_cancel_monoid M] :
add_left_cancel_monoid M

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@[instance]
def cancel_monoid.to_right_cancel_monoid (M : Type u) [s : cancel_monoid M] :
right_cancel_monoid M

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@[class]
structure cancel_monoid (M : Type u) :
Type u
  • mul : M → M → M
  • mul_assoc : ∀ (a b c_1 : M), (a * b) * c_1 = a * b * c_1
  • mul_left_cancel : ∀ (a b c_1 : M), a * b = a * c_1 → b = c_1
  • one : M
  • one_mul : ∀ (a : M), 1 * a = a
  • mul_one : ∀ (a : M), a * 1 = a
  • mul_right_cancel : ∀ (a b c_1 : M), a * b = c_1 * b → a = c_1

A monoid in which multiplication is cancellative.

Instances
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@[instance]
def cancel_monoid.to_left_cancel_monoid (M : Type u) [s : cancel_monoid M] :
left_cancel_monoid M

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@[instance]
def add_cancel_comm_monoid.to_add_left_cancel_comm_monoid (M : Type u) [s : add_cancel_comm_monoid M] :
add_left_cancel_comm_monoid M

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@[class]
structure add_cancel_comm_monoid (M : Type u) :
Type u
  • add : M → M → M
  • add_assoc : ∀ (a b c_1 : M), a + b + c_1 = a + (b + c_1)
  • add_left_cancel : ∀ (a b c_1 : M), a + b = a + c_1 → b = c_1
  • zero : M
  • zero_add : ∀ (a : M), 0 + a = a
  • add_zero : ∀ (a : M), a + 0 = a
  • add_comm : ∀ (a b : M), a + b = b + a
  • add_right_cancel : ∀ (a b c_1 : M), a + b = c_1 + b → a = c_1

Commutative version of add_cancel_monoid.

Instances
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@[instance]
def add_cancel_comm_monoid.to_add_right_cancel_comm_monoid (M : Type u) [s : add_cancel_comm_monoid M] :
add_right_cancel_comm_monoid M

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@[class]
structure cancel_comm_monoid (M : Type u) :
Type u
  • mul : M → M → M
  • mul_assoc : ∀ (a b c_1 : M), (a * b) * c_1 = a * b * c_1
  • mul_left_cancel : ∀ (a b c_1 : M), a * b = a * c_1 → b = c_1
  • one : M
  • one_mul : ∀ (a : M), 1 * a = a
  • mul_one : ∀ (a : M), a * 1 = a
  • mul_comm : ∀ (a b : M), a * b = b * a
  • mul_right_cancel : ∀ (a b c_1 : M), a * b = c_1 * b → a = c_1

Commutative version of cancel_monoid.

Instances
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@[instance]
def cancel_comm_monoid.to_right_cancel_comm_monoid (M : Type u) [s : cancel_comm_monoid M] :
right_cancel_comm_monoid M

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@[instance]
def cancel_comm_monoid.to_left_cancel_comm_monoid (M : Type u) [s : cancel_comm_monoid M] :
left_cancel_comm_monoid M

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meta def try_refl_tac  :
tactic unit

try_refl_tac solves goals of the form ∀ a b, f a b = g a b, if they hold by definition.

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@[instance]
def div_inv_monoid.to_monoid (G : Type u) [s : div_inv_monoid G] :
monoid G

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@[instance]
def div_inv_monoid.to_has_div (G : Type u) [s : div_inv_monoid G] :
has_div G

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@[class]
structure div_inv_monoid (G : Type u) :
Type u
  • mul : G → G → G
  • mul_assoc : ∀ (a b c_1 : G), (a * b) * c_1 = a * b * c_1
  • one : G
  • one_mul : ∀ (a : G), 1 * a = a
  • mul_one : ∀ (a : G), a * 1 = a
  • inv : G → G
  • div : G → G → G
  • div_eq_mul_inv : (∀ (a b : G), a / b = a * b⁻¹) . "try_refl_tac"

A div_inv_monoid is a monoid with operations / and ⁻¹ satisfying div_eq_mul_inv : ∀ a b, a / b = a * b⁻¹.

This is the immediate common ancestor of group and group_with_zero, in order to deduplicate the name div_eq_mul_inv. The default for div is such that a / b = a * b⁻¹ holds by definition.

Adding div as a field rather than defining a / b := a * b⁻¹ allows us to avoid certain classes of unification failures, for example: Let foo X be a type with a ∀ X, has_div (foo X) instance but no ∀ X, has_inv (foo X), e.g. when foo X is a euclidean_domain. Suppose we also have an instance ∀ X [cromulent X], group_with_zero (foo X). Then the (/) coming from group_with_zero_has_div cannot be definitionally equal to the (/) coming from foo.has_div.

Instances
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@[instance]
def div_inv_monoid.to_has_inv (G : Type u) [s : div_inv_monoid G] :
has_inv G

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@[instance]
def sub_neg_monoid.to_has_sub (G : Type u) [s : sub_neg_monoid G] :
has_sub G

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@[instance]
def sub_neg_monoid.to_add_monoid (G : Type u) [s : sub_neg_monoid G] :
add_monoid G

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@[class]
structure sub_neg_monoid (G : Type u) :
Type u
  • add : G → G → G
  • add_assoc : ∀ (a b c_1 : G), a + b + c_1 = a + (b + c_1)
  • zero : G
  • zero_add : ∀ (a : G), 0 + a = a
  • add_zero : ∀ (a : G), a + 0 = a
  • neg : G → G
  • sub : G → G → G
  • sub_eq_add_neg : (∀ (a b : G), a - b = a + -b) . "try_refl_tac"

A sub_neg_monoid is an add_monoid with unary - and binary - operations satisfying sub_eq_add_neg : ∀ a b, a - b = a + -b.

The default for sub is such that a - b = a + -b holds by definition.

Adding sub as a field rather than defining a - b := a + -b allows us to avoid certain classes of unification failures, for example: Let foo X be a type with a ∀ X, has_sub (foo X) instance but no ∀ X, has_neg (foo X). Suppose we also have an instance ∀ X [cromulent X], add_group (foo X). Then the (-) coming from add_group.has_sub cannot be definitionally equal to the (-) coming from foo.has_sub.

Instances
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@[instance]
def sub_neg_monoid.to_has_neg (G : Type u) [s : sub_neg_monoid G] :
has_neg G

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theorem div_eq_mul_inv {G : Type u} [div_inv_monoid G] (a b : G) :
a / b = a * b⁻¹

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theorem sub_eq_add_neg {G : Type u} [sub_neg_monoid G] (a b : G) :
a - b = a + -b

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@[class]
structure group (G : Type u) :
Type u
  • mul : G → G → G
  • mul_assoc : ∀ (a b c_1 : G), (a * b) * c_1 = a * b * c_1
  • one : G
  • one_mul : ∀ (a : G), 1 * a = a
  • mul_one : ∀ (a : G), a * 1 = a
  • inv : G → G
  • div : G → G → G
  • div_eq_mul_inv : (∀ (a b : G), a / b = a * b⁻¹) . "try_refl_tac"
  • mul_left_inv : ∀ (a : G), a⁻¹ * a = 1

A group is a monoid with an operation ⁻¹ satisfying a⁻¹ * a = 1.

There is also a division operation / such that a / b = a * b⁻¹, with a default so that a / b = a * b⁻¹ holds by definition.

Instances
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@[instance]
def group.to_div_inv_monoid (G : Type u) [s : group G] :
div_inv_monoid G

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@[class]
structure add_group (A : Type u) :
Type u
  • add : A → A → A
  • add_assoc : ∀ (a b c_1 : A), a + b + c_1 = a + (b + c_1)
  • zero : A
  • zero_add : ∀ (a : A), 0 + a = a
  • add_zero : ∀ (a : A), a + 0 = a
  • neg : A → A
  • sub : A → A → A
  • sub_eq_add_neg : (∀ (a b : A), a - b = a + -b) . "try_refl_tac"
  • add_left_neg : ∀ (a : A), -a + a = 0

An add_group is an add_monoid with a unary - satisfying -a + a = 0.

There is also a binary operation - such that a - b = a + -b, with a default so that a - b = a + -b holds by definition.

Instances
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@[instance]
def add_group.to_sub_neg_monoid (A : Type u) [s : add_group A] :
sub_neg_monoid A

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def add_group.to_add_monoid (G : Type u) [add_group G] :
add_monoid G

Abbreviation for @sub_neg_monoid.to_add_monoid _ (@add_group.to_sub_neg_monoid _ _).

Useful because it corresponds to the fact that AddGroup is a subcategory of AddMon. Not an instance since it duplicates @sub_neg_monoid.to_add_monoid _ (@add_group.to_sub_neg_monoid _ _).

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def group.to_monoid (G : Type u) [group G] :
monoid G

Abbreviation for @div_inv_monoid.to_monoid _ (@group.to_div_inv_monoid _ _).

Useful because it corresponds to the fact that Grp is a subcategory of Mon. Not an instance since it duplicates @div_inv_monoid.to_monoid _ (@group.to_div_inv_monoid _ _).

Equations
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@[simp]
theorem add_left_neg {G : Type u} [add_group G] (a : G) :
-a + a = 0

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@[simp]
theorem mul_left_inv {G : Type u} [group G] (a : G) :
a⁻¹ * a = 1

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theorem neg_add_self {G : Type u} [add_group G] (a : G) :
-a + a = 0

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theorem inv_mul_self {G : Type u} [group G] (a : G) :
a⁻¹ * a = 1

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@[simp]
theorem inv_mul_cancel_left {G : Type u} [group G] (a b : G) :
a⁻¹ * a * b = b

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@[simp]
theorem neg_add_cancel_left {G : Type u} [add_group G] (a b : G) :
-a + (a + b) = b

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@[simp]
theorem inv_eq_of_mul_eq_one {G : Type u} [group G] {a b : G} (h : a * b = 1) :
a⁻¹ = b

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@[simp]
theorem neg_eq_of_add_eq_zero {G : Type u} [add_group G] {a b : G} (h : a + b = 0) :
-a = b

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@[simp]
theorem inv_inv {G : Type u} [group G] (a : G) :
a⁻¹⁻¹ = a

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@[simp]
theorem neg_neg {G : Type u} [add_group G] (a : G) :
--a = a

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@[simp]
theorem mul_right_inv {G : Type u} [group G] (a : G) :
a * a⁻¹ = 1

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@[simp]
theorem add_right_neg {G : Type u} [add_group G] (a : G) :
a + -a = 0

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theorem add_neg_self {G : Type u} [add_group G] (a : G) :
a + -a = 0

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theorem mul_inv_self {G : Type u} [group G] (a : G) :
a * a⁻¹ = 1

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@[simp]
theorem add_neg_cancel_right {G : Type u} [add_group G] (a b : G) :
a + b + -b = a

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@[simp]
theorem mul_inv_cancel_right {G : Type u} [group G] (a b : G) :
(a * b) * b⁻¹ = a

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@[instance]
def group.to_cancel_monoid {G : Type u} [group G] :
cancel_monoid G

Equations
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@[instance]
def add_group.to_cancel_add_monoid {G : Type u} [add_group G] :
add_cancel_monoid G

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@[instance]
def comm_group.to_group (G : Type u) [s : comm_group G] :
group G

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@[class]
structure comm_group (G : Type u) :
Type u
  • mul : G → G → G
  • mul_assoc : ∀ (a b c_1 : G), (a * b) * c_1 = a * b * c_1
  • one : G
  • one_mul : ∀ (a : G), 1 * a = a
  • mul_one : ∀ (a : G), a * 1 = a
  • inv : G → G
  • div : G → G → G
  • div_eq_mul_inv : (∀ (a b : G), a / b = a * b⁻¹) . "try_refl_tac"
  • mul_left_inv : ∀ (a : G), a⁻¹ * a = 1
  • mul_comm : ∀ (a b : G), a * b = b * a

A commutative group is a group with commutative (*).

Instances
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@[instance]
def comm_group.to_comm_monoid (G : Type u) [s : comm_group G] :
comm_monoid G

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@[class]
structure add_comm_group (G : Type u) :
Type u
  • add : G → G → G
  • add_assoc : ∀ (a b c_1 : G), a + b + c_1 = a + (b + c_1)
  • zero : G
  • zero_add : ∀ (a : G), 0 + a = a
  • add_zero : ∀ (a : G), a + 0 = a
  • neg : G → G
  • sub : G → G → G
  • sub_eq_add_neg : (∀ (a b : G), a - b = a + -b) . "try_refl_tac"
  • add_left_neg : ∀ (a : G), -a + a = 0
  • add_comm : ∀ (a b : G), a + b = b + a

An additive commutative group is an additive group with commutative (+).

Instances
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@[instance]
def add_comm_group.to_add_comm_monoid (G : Type u) [s : add_comm_group G] :
add_comm_monoid G

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@[instance]
def add_comm_group.to_add_group (G : Type u) [s : add_comm_group G] :
add_group G

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@[instance]
def comm_group.to_cancel_comm_monoid {G : Type u} [comm_group G] :
cancel_comm_monoid G

Equations
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@[instance]
def add_comm_group.to_cancel_add_comm_monoid {G : Type u} [add_comm_group G] :
add_cancel_comm_monoid G