Subsemigroups: definition

This file defines bundled multiplicative and additive subsemigroups.

Main definitions

• Subsemigroup M: the type of bundled subsemigroup of a magma M; the underlying set is given in the carrier field of the structure, and should be accessed through coercion as in (S : Set M).
• AddSubsemigroup M : the type of bundled subsemigroups of an additive magma M.

For each of the following definitions in the Subsemigroup namespace, there is a corresponding definition in the AddSubsemigroup namespace.

• Subsemigroup.copy : copy of a subsemigroup with carrier replaced by a set that is equal but possibly not definitionally equal to the carrier of the original Subsemigroup.

Similarly, for each of these definitions in the MulHom namespace, there is a corresponding definition in the AddHom namespace.

• MulHom.eqLocus f g: the subsemigroup of those x such that f x = g x

Implementation notes

Subsemigroup inclusion is denoted ≤ rather than ⊆, although ∈ is defined as membership of a subsemigroup's underlying set.

Note that Subsemigroup M does not actually require Semigroup M, instead requiring only the weaker Mul M.

This file is designed to have very few dependencies. In particular, it should not use natural numbers.

Tags

subsemigroup, subsemigroups

class MulMemClass (S : Type u_3) (M : outParam (Type u_4)) [Mul M] [SetLike S M] : Prop

MulMemClass S M says S is a type of sets s : Set M that are closed under (*)

• mul_mem : ∀ {s : S} {a b : M}, a ∈ s → b ∈ s → a * b ∈ s

  A substructure satisfying MulMemClass is closed under multiplication.

theorem MulMemClass.mul_mem {S : Type u_3} {M : outParam (Type u_4)} : ∀ {inst : Mul M} {inst_1 : SetLike S M} [self : MulMemClass S M] {s : S} {a b : M}, a ∈ s → b ∈ s → a * b ∈ s

A substructure satisfying MulMemClass is closed under multiplication.

class AddMemClass (S : Type u_3) (M : outParam (Type u_4)) [Add M] [SetLike S M] : Prop

AddMemClass S M says S is a type of sets s : Set M that are closed under (+)

• add_mem : ∀ {s : S} {a b : M}, a ∈ s → b ∈ s → a + b ∈ s

  A substructure satisfying AddMemClass is closed under addition.

theorem AddMemClass.add_mem {S : Type u_3} {M : outParam (Type u_4)} : ∀ {inst : Add M} {inst_1 : SetLike S M} [self : AddMemClass S M] {s : S} {a b : M}, a ∈ s → b ∈ s → a + b ∈ s

A substructure satisfying AddMemClass is closed under addition.

structure Subsemigroup (M : Type u_3) [Mul M] : Type u_3

A subsemigroup of a magma M is a subset closed under multiplication.

• carrier : Set M

  The carrier of a subsemigroup.

• mul_mem' : ∀ {a b : M}, a ∈ self.carrier → b ∈ self.carrier → a * b ∈ self.carrier

  The product of two elements of a subsemigroup belongs to the subsemigroup.

theorem Subsemigroup.mul_mem' {M : Type u_3} [Mul M] (self : Subsemigroup M) {a : M} {b : M} : a ∈ self.carrier → b ∈ self.carrier → a * b ∈ self.carrier

The product of two elements of a subsemigroup belongs to the subsemigroup.

structure AddSubsemigroup (M : Type u_3) [Add M] : Type u_3

An additive subsemigroup of an additive magma M is a subset closed under addition.

• carrier : Set M

  The carrier of an additive subsemigroup.

• add_mem' : ∀ {a b : M}, a ∈ self.carrier → b ∈ self.carrier → a + b ∈ self.carrier

  The sum of two elements of an additive subsemigroup belongs to the subsemigroup.

theorem AddSubsemigroup.add_mem' {M : Type u_3} [Add M] (self : AddSubsemigroup M) {a : M} {b : M} : a ∈ self.carrier → b ∈ self.carrier → a + b ∈ self.carrier

The sum of two elements of an additive subsemigroup belongs to the subsemigroup.

instance AddSubsemigroup.instSetLike {M : Type u_1} [Add M] : SetLike (AddSubsemigroup M) M

Equations

• AddSubsemigroup.instSetLike = { coe := AddSubsemigroup.carrier, coe_injective' := ⋯ }

instance Subsemigroup.instSetLike {M : Type u_1} [Mul M] : SetLike (Subsemigroup M) M

Equations

• Subsemigroup.instSetLike = { coe := Subsemigroup.carrier, coe_injective' := ⋯ }

instance AddSubsemigroup.instAddMemClass {M : Type u_1} [Add M] : AddMemClass (AddSubsemigroup M) M

Equations

• ⋯ = ⋯

instance Subsemigroup.instMulMemClass {M : Type u_1} [Mul M] : MulMemClass (Subsemigroup M) M

Equations

• ⋯ = ⋯

@[simp]

theorem AddSubsemigroup.mem_carrier {M : Type u_1} [Add M] {s : AddSubsemigroup M} {x : M} : x ∈ s.carrier ↔ x ∈ s

@[simp]

theorem Subsemigroup.mem_carrier {M : Type u_1} [Mul M] {s : Subsemigroup M} {x : M} : x ∈ s.carrier ↔ x ∈ s

@[simp]

theorem AddSubsemigroup.mem_mk {M : Type u_1} [Add M] {s : Set M} {x : M} (h_mul : ∀ {a b : M}, a ∈ s → b ∈ s → a + b ∈ s) : x ∈ { carrier := s, add_mem' := h_mul } ↔ x ∈ s

@[simp]

theorem Subsemigroup.mem_mk {M : Type u_1} [Mul M] {s : Set M} {x : M} (h_mul : ∀ {a b : M}, a ∈ s → b ∈ s → a * b ∈ s) : x ∈ { carrier := s, mul_mem' := h_mul } ↔ x ∈ s

@[simp]

theorem AddSubsemigroup.coe_set_mk {M : Type u_1} [Add M] (s : Set M) (h_mul : ∀ {a b : M}, a ∈ s → b ∈ s → a + b ∈ s) : ↑{ carrier := s, add_mem' := h_mul } = s

@[simp]

theorem Subsemigroup.coe_set_mk {M : Type u_1} [Mul M] (s : Set M) (h_mul : ∀ {a b : M}, a ∈ s → b ∈ s → a * b ∈ s) : ↑{ carrier := s, mul_mem' := h_mul } = s

@[simp]

theorem AddSubsemigroup.mk_le_mk {M : Type u_1} [Add M] {s : Set M} {t : Set M} (h_mul : ∀ {a b : M}, a ∈ s → b ∈ s → a + b ∈ s) (h_mul' : ∀ {a b : M}, a ∈ t → b ∈ t → a + b ∈ t) : { carrier := s, add_mem' := h_mul } ≤ { carrier := t, add_mem' := h_mul' } ↔ s ⊆ t

@[simp]

theorem Subsemigroup.mk_le_mk {M : Type u_1} [Mul M] {s : Set M} {t : Set M} (h_mul : ∀ {a b : M}, a ∈ s → b ∈ s → a * b ∈ s) (h_mul' : ∀ {a b : M}, a ∈ t → b ∈ t → a * b ∈ t) : { carrier := s, mul_mem' := h_mul } ≤ { carrier := t, mul_mem' := h_mul' } ↔ s ⊆ t

theorem AddSubsemigroup.ext {M : Type u_1} [Add M] {S : AddSubsemigroup M} {T : AddSubsemigroup M} (h : ∀ (x : M), x ∈ S ↔ x ∈ T) : S = T

Two AddSubsemigroups are equal if they have the same elements.

theorem AddSubsemigroup.ext_iff {M : Type u_1} [Add M] {S : AddSubsemigroup M} {T : AddSubsemigroup M} : S = T ↔ ∀ (x : M), x ∈ S ↔ x ∈ T

theorem Subsemigroup.ext_iff {M : Type u_1} [Mul M] {S : Subsemigroup M} {T : Subsemigroup M} : S = T ↔ ∀ (x : M), x ∈ S ↔ x ∈ T

theorem Subsemigroup.ext {M : Type u_1} [Mul M] {S : Subsemigroup M} {T : Subsemigroup M} (h : ∀ (x : M), x ∈ S ↔ x ∈ T) : S = T

Two subsemigroups are equal if they have the same elements.

def AddSubsemigroup.copy {M : Type u_1} [Add M] (S : AddSubsemigroup M) (s : Set M) (hs : s = ↑S) : AddSubsemigroup M

Copy an additive subsemigroup replacing carrier with a set that is equal to it.

Equations

• S.copy s hs = { carrier := s, add_mem' := ⋯ }

def Subsemigroup.copy {M : Type u_1} [Mul M] (S : Subsemigroup M) (s : Set M) (hs : s = ↑S) : Subsemigroup M

Copy a subsemigroup replacing carrier with a set that is equal to it.

Equations

• S.copy s hs = { carrier := s, mul_mem' := ⋯ }

@[simp]

theorem AddSubsemigroup.coe_copy {M : Type u_1} [Add M] {S : AddSubsemigroup M} {s : Set M} (hs : s = ↑S) : ↑(S.copy s hs) = s

@[simp]

theorem Subsemigroup.coe_copy {M : Type u_1} [Mul M] {S : Subsemigroup M} {s : Set M} (hs : s = ↑S) : ↑(S.copy s hs) = s

theorem AddSubsemigroup.copy_eq {M : Type u_1} [Add M] {S : AddSubsemigroup M} {s : Set M} (hs : s = ↑S) : S.copy s hs = S

theorem Subsemigroup.copy_eq {M : Type u_1} [Mul M] {S : Subsemigroup M} {s : Set M} (hs : s = ↑S) : S.copy s hs = S

theorem AddSubsemigroup.add_mem {M : Type u_1} [Add M] (S : AddSubsemigroup M) {x : M} {y : M} : x ∈ S → y ∈ S → x + y ∈ S

An AddSubsemigroup is closed under addition.

theorem Subsemigroup.mul_mem {M : Type u_1} [Mul M] (S : Subsemigroup M) {x : M} {y : M} : x ∈ S → y ∈ S → x * y ∈ S

A subsemigroup is closed under multiplication.

instance AddSubsemigroup.instTop {M : Type u_1} [Add M] : Top (AddSubsemigroup M)

The additive subsemigroup M of the magma M.

Equations

• AddSubsemigroup.instTop = { top := { carrier := Set.univ, add_mem' := ⋯ } }

instance Subsemigroup.instTop {M : Type u_1} [Mul M] : Top (Subsemigroup M)

The subsemigroup M of the magma M.

Equations

• Subsemigroup.instTop = { top := { carrier := Set.univ, mul_mem' := ⋯ } }

instance AddSubsemigroup.instBot {M : Type u_1} [Add M] : Bot (AddSubsemigroup M)

The trivial AddSubsemigroup ∅ of an additive magma M.

Equations

• AddSubsemigroup.instBot = { bot := { carrier := ∅, add_mem' := ⋯ } }

instance Subsemigroup.instBot {M : Type u_1} [Mul M] : Bot (Subsemigroup M)

The trivial subsemigroup ∅ of a magma M.

Equations

• Subsemigroup.instBot = { bot := { carrier := ∅, mul_mem' := ⋯ } }

instance AddSubsemigroup.instInhabited {M : Type u_1} [Add M] : Inhabited (AddSubsemigroup M)

Equations

• AddSubsemigroup.instInhabited = { default := ⊥ }

instance Subsemigroup.instInhabited {M : Type u_1} [Mul M] : Inhabited (Subsemigroup M)

Equations

• Subsemigroup.instInhabited = { default := ⊥ }

theorem AddSubsemigroup.not_mem_bot {M : Type u_1} [Add M] {x : M} : x ∉ ⊥

theorem Subsemigroup.not_mem_bot {M : Type u_1} [Mul M] {x : M} : x ∉ ⊥

@[simp]

theorem AddSubsemigroup.mem_top {M : Type u_1} [Add M] (x : M) : x ∈ ⊤

@[simp]

theorem Subsemigroup.mem_top {M : Type u_1} [Mul M] (x : M) : x ∈ ⊤

@[simp]

theorem AddSubsemigroup.coe_top {M : Type u_1} [Add M] : ↑⊤ = Set.univ

@[simp]

theorem Subsemigroup.coe_top {M : Type u_1} [Mul M] : ↑⊤ = Set.univ

@[simp]

theorem AddSubsemigroup.coe_bot {M : Type u_1} [Add M] : ↑⊥ = ∅

@[simp]

theorem Subsemigroup.coe_bot {M : Type u_1} [Mul M] : ↑⊥ = ∅

instance AddSubsemigroup.instInf {M : Type u_1} [Add M] : Inf (AddSubsemigroup M)

The inf of two AddSubsemigroups is their intersection.

Equations

• AddSubsemigroup.instInf = { inf := fun (S₁ S₂ : AddSubsemigroup M) => { carrier := ↑S₁ ∩ ↑S₂, add_mem' := ⋯ } }

instance Subsemigroup.instInf {M : Type u_1} [Mul M] : Inf (Subsemigroup M)

The inf of two subsemigroups is their intersection.

Equations

• Subsemigroup.instInf = { inf := fun (S₁ S₂ : Subsemigroup M) => { carrier := ↑S₁ ∩ ↑S₂, mul_mem' := ⋯ } }

@[simp]

theorem AddSubsemigroup.coe_inf {M : Type u_1} [Add M] (p : AddSubsemigroup M) (p' : AddSubsemigroup M) : ↑(p ⊓ p') = ↑p ∩ ↑p'

@[simp]

theorem Subsemigroup.coe_inf {M : Type u_1} [Mul M] (p : Subsemigroup M) (p' : Subsemigroup M) : ↑(p ⊓ p') = ↑p ∩ ↑p'

@[simp]

theorem AddSubsemigroup.mem_inf {M : Type u_1} [Add M] {p : AddSubsemigroup M} {p' : AddSubsemigroup M} {x : M} : x ∈ p ⊓ p' ↔ x ∈ p ∧ x ∈ p'

@[simp]

theorem Subsemigroup.mem_inf {M : Type u_1} [Mul M] {p : Subsemigroup M} {p' : Subsemigroup M} {x : M} : x ∈ p ⊓ p' ↔ x ∈ p ∧ x ∈ p'

theorem AddSubsemigroup.subsingleton_of_subsingleton {M : Type u_1} [Add M] [Subsingleton (AddSubsemigroup M)] : Subsingleton M

theorem Subsemigroup.subsingleton_of_subsingleton {M : Type u_1} [Mul M] [Subsingleton (Subsemigroup M)] : Subsingleton M

instance AddSubsemigroup.instNontrivialOfNonempty {M : Type u_1} [Add M] [hn : Nonempty M] : Nontrivial (AddSubsemigroup M)

Equations

• ⋯ = ⋯

instance Subsemigroup.instNontrivialOfNonempty {M : Type u_1} [Mul M] [hn : Nonempty M] : Nontrivial (Subsemigroup M)

Equations

• ⋯ = ⋯

def AddHom.eqLocus {M : Type u_1} {N : Type u_2} [Add M] [Add N] (f : AddHom M N) (g : AddHom M N) : AddSubsemigroup M

The additive subsemigroup of elements x : M such that f x = g x

Equations

• f.eqLocus g = { carrier := {x : M | f x = g x}, add_mem' := ⋯ }

def MulHom.eqLocus {M : Type u_1} {N : Type u_2} [Mul M] [Mul N] (f : M →ₙ* N) (g : M →ₙ* N) : Subsemigroup M

The subsemigroup of elements x : M such that f x = g x

Equations

• f.eqLocus g = { carrier := {x : M | f x = g x}, mul_mem' := ⋯ }

theorem AddHom.eq_of_eqOn_top {M : Type u_1} {N : Type u_2} [Add M] [Add N] {f : AddHom M N} {g : AddHom M N} (h : Set.EqOn ⇑f ⇑g ↑⊤) : f = g

theorem MulHom.eq_of_eqOn_top {M : Type u_1} {N : Type u_2} [Mul M] [Mul N] {f : M →ₙ* N} {g : M →ₙ* N} (h : Set.EqOn ⇑f ⇑g ↑⊤) : f = g