mathlib documentation

group_theory.congruence

Congruence relations

This file defines congruence relations: equivalence relations that preserve a binary operation, which in this case is multiplication or addition. The principal definition is a structure extending a setoid (an equivalence relation), and the inductive definition of the smallest congruence relation containing a binary relation is also given (see con_gen).

The file also proves basic properties of the quotient of a type by a congruence relation, and the complete lattice of congruence relations on a type. We then establish an order-preserving bijection between the set of congruence relations containing a congruence relation c and the set of congruence relations on the quotient by c.

The second half of the file concerns congruence relations on monoids, in which case the quotient by the congruence relation is also a monoid. There are results about the universal property of quotients of monoids, and the isomorphism theorems for monoids.

Implementation notes

The inductive definition of a congruence relation could be a nested inductive type, defined using the equivalence closure of a binary relation eqv_gen, but the recursor generated does not work. A nested inductive definition could conceivably shorten proofs, because they would allow invocation of the corresponding lemmas about eqv_gen.

The lemmas refl, symm and trans are not tagged with @[refl], @[symm], and @[trans] respectively as these tags do not work on a structure coerced to a binary relation.

There is a coercion from elements of a type to the element's equivalence class under a congruence relation.

A congruence relation on a monoid M can be thought of as a submonoid of M × M for which membership is an equivalence relation, but whilst this fact is established in the file, it is not used, since this perspective adds more layers of definitional unfolding.

Tags

congruence, congruence relation, quotient, quotient by congruence relation, monoid, quotient monoid, isomorphism theorems

structure add_con (M : Type u_1) [has_add M] :
Type u_1
  • r : M → M → Prop
  • iseqv : equivalence c.r
  • add' : ∀ {w x y z : M}, c.r w xc.r y zc.r (w + y) (x + z)

A congruence relation on a type with an addition is an equivalence relation which preserves addition.

def add_con.to_setoid {M : Type u_1} [has_add M] :
add_con Msetoid M

The equivalence relation underlying an additive congruence relation.

def con.to_setoid {M : Type u_1} [has_mul M] :
con Msetoid M

The equivalence relation underlying a multiplicative congruence relation.

structure con (M : Type u_1) [has_mul M] :
Type u_1
  • r : M → M → Prop
  • iseqv : equivalence c.r
  • mul' : ∀ {w x y z : M}, c.r w xc.r y zc.r (w * y) (x * z)

A congruence relation on a type with a multiplication is an equivalence relation which preserves multiplication.

inductive add_con_gen.rel {M : Type u_1} [has_add M] :
(M → M → Prop)M → M → Prop

The inductively defined smallest additive congruence relation containing a given binary relation.

inductive con_gen.rel {M : Type u_1} [has_mul M] :
(M → M → Prop)M → M → Prop

The inductively defined smallest multiplicative congruence relation containing a given binary relation.

def add_con_gen {M : Type u_1} [has_add M] :
(M → M → Prop)add_con M

The inductively defined smallest additive congruence relation containing a given binary relation.

def con_gen {M : Type u_1} [has_mul M] :
(M → M → Prop)con M

The inductively defined smallest multiplicative congruence relation containing a given binary relation.

Equations
@[instance]
def con.inhabited {M : Type u_1} [has_mul M] :

Equations
@[instance]
def add_con.inhabited {M : Type u_1} [has_add M] :

@[instance]
def add_con.has_coe_to_fun {M : Type u_1} [has_add M] :

A coercion from an additive congruence relation to its underlying binary relation.

@[instance]
def con.has_coe_to_fun {M : Type u_1} [has_mul M] :

A coercion from a congruence relation to its underlying binary relation.

Equations
@[simp]
theorem con.rel_eq_coe {M : Type u_1} [has_mul M] (c : con M) :
c.r = c

@[simp]
theorem add_con.rel_eq_coe {M : Type u_1} [has_add M] (c : add_con M) :
c.r = c

theorem con.refl {M : Type u_1} [has_mul M] (c : con M) (x : M) :
c x x

Congruence relations are reflexive.

theorem add_con.refl {M : Type u_1} [has_add M] (c : add_con M) (x : M) :
c x x

Additive congruence relations are reflexive.

theorem add_con.symm {M : Type u_1} [has_add M] (c : add_con M) {x y : M} :
c x yc y x

Additive congruence relations are symmetric.

theorem con.symm {M : Type u_1} [has_mul M] (c : con M) {x y : M} :
c x yc y x

Congruence relations are symmetric.

theorem add_con.trans {M : Type u_1} [has_add M] (c : add_con M) {x y z : M} :
c x yc y zc x z

Additive congruence relations are transitive.

theorem con.trans {M : Type u_1} [has_mul M] (c : con M) {x y z : M} :
c x yc y zc x z

Congruence relations are transitive.

theorem con.mul {M : Type u_1} [has_mul M] (c : con M) {w x y z : M} :
c w xc y zc (w * y) (x * z)

Multiplicative congruence relations preserve multiplication.

theorem add_con.add {M : Type u_1} [has_add M] (c : add_con M) {w x y z : M} :
c w xc y zc (w + y) (x + z)

Additive congruence relations preserve addition.

@[instance]
def con.has_mem {M : Type u_1} [has_mul M] :
has_mem (M × M) (con M)

Given a type M with a multiplication, a congruence relation c on M, and elements of M x, y, (x, y) ∈ M × M iff x is related to y by c.

Equations
@[instance]
def add_con.has_mem {M : Type u_1} [has_add M] :
has_mem (M × M) (add_con M)

Given a type M with an addition, x, y ∈ M, and an additive congruence relation c on M, (x, y) ∈ M × M iff x is related to y by c.

theorem con.ext' {M : Type u_1} [has_mul M] {c d : con M} :
c.r = d.rc = d

The map sending a congruence relation to its underlying binary relation is injective.

theorem add_con.ext' {M : Type u_1} [has_add M] {c d : add_con M} :
c.r = d.rc = d

The map sending an additive congruence relation to its underlying binary relation is injective.

@[ext]
theorem con.ext {M : Type u_1} [has_mul M] {c d : con M} :
(∀ (x y : M), c x y d x y)c = d

Extensionality rule for congruence relations.

@[ext]
theorem add_con.ext {M : Type u_1} [has_add M] {c d : add_con M} :
(∀ (x y : M), c x y d x y)c = d

Extensionality rule for additive congruence relations.

theorem con.to_setoid_inj {M : Type u_1} [has_mul M] {c d : con M} :
c.to_setoid = d.to_setoidc = d

The map sending a congruence relation to its underlying equivalence relation is injective.

theorem add_con.to_setoid_inj {M : Type u_1} [has_add M] {c d : add_con M} :
c.to_setoid = d.to_setoidc = d

The map sending an additive congruence relation to its underlying equivalence relation is injective.

theorem add_con.ext_iff {M : Type u_1} [has_add M] {c d : add_con M} :
(∀ (x y : M), c x y d x y) c = d

Iff version of extensionality rule for additive congruence relations.

theorem con.ext_iff {M : Type u_1} [has_mul M] {c d : con M} :
(∀ (x y : M), c x y d x y) c = d

Iff version of extensionality rule for congruence relations.

theorem con.ext'_iff {M : Type u_1} [has_mul M] {c d : con M} :
c.r = d.r c = d

Two congruence relations are equal iff their underlying binary relations are equal.

theorem add_con.ext'_iff {M : Type u_1} [has_add M] {c d : add_con M} :
c.r = d.r c = d

Two additive congruence relations are equal iff their underlying binary relations are equal.

def add_con.add_ker {M : Type u_1} {P : Type u_3} [has_add M] [has_add P] (f : M → P) :
(∀ (x y : M), f (x + y) = f x + f y)add_con M

The kernel of an addition-preserving function as an additive congruence relation.

def con.mul_ker {M : Type u_1} {P : Type u_3} [has_mul M] [has_mul P] (f : M → P) :
(∀ (x y : M), f (x * y) = (f x) * f y)con M

The kernel of a multiplication-preserving function as a congruence relation.

Equations
def con.prod {M : Type u_1} {N : Type u_2} [has_mul M] [has_mul N] :
con Mcon Ncon (M × N)

Given types with multiplications M, N, the product of two congruence relations c on M and d on N: (x₁, x₂), (y₁, y₂) ∈ M × N are related by c.prod d iff x₁ is related to y₁ by c and x₂ is related to y₂ by d.

Equations
def add_con.prod {M : Type u_1} {N : Type u_2} [has_add M] [has_add N] :
add_con Madd_con Nadd_con (M × N)

Given types with additions M, N, the product of two congruence relations c on M and d on N: (x₁, x₂), (y₁, y₂) ∈ M × N are related by c.prod d iff x₁ is related to y₁ by c and x₂ is related to y₂ by d.

def con.pi {ι : Type u_1} {f : ι → Type u_2} [Π (i : ι), has_mul (f i)] :
(Π (i : ι), con (f i))con (Π (i : ι), f i)

The product of an indexed collection of congruence relations.

Equations
def add_con.pi {ι : Type u_1} {f : ι → Type u_2} [Π (i : ι), has_add (f i)] :
(Π (i : ι), add_con (f i))add_con (Π (i : ι), f i)

The product of an indexed collection of additive congruence relations.

@[simp]
theorem con.coe_eq {M : Type u_1} [has_mul M] (c : con M) :

@[simp]
theorem add_con.coe_eq {M : Type u_1} [has_add M] (c : add_con M) :

def add_con.quotient {M : Type u_1} [has_add M] :
add_con MType u_1

Defining the quotient by an additive congruence relation of a type with an addition.

def con.quotient {M : Type u_1} [has_mul M] :
con MType u_1

Defining the quotient by a congruence relation of a type with a multiplication.

Equations
@[instance]
def con.quotient.has_coe_t {M : Type u_1} [has_mul M] (c : con M) :

Coercion from a type with a multiplication to its quotient by a congruence relation.

See Note [use has_coe_t].

Equations
@[instance]
def add_con.quotient.has_coe_t {M : Type u_1} [has_add M] (c : add_con M) :

Coercion from a type with an addition to its quotient by an additive congruence relation

@[instance]
def con.quotient.decidable_eq {M : Type u_1} [has_mul M] (c : con M) [d : Π (a b : M), decidable (c a b)] :

The quotient of a type with decidable equality by a congruence relation also has decidable equality.

Equations
@[instance]
def add_con.quotient.decidable_eq {M : Type u_1} [has_add M] (c : add_con M) [d : Π (a b : M), decidable (c a b)] :

The quotient of a type with decidable equality by an additive congruence relation also has decidable equality.

def con.lift_on {M : Type u_1} [has_mul M] {β : Sort u_2} {c : con M} (q : c.quotient) (f : M → β) :
(∀ (a b : M), c a bf a = f b) → β

The function on the quotient by a congruence relation c induced by a function that is constant on c's equivalence classes.

Equations
def add_con.lift_on {M : Type u_1} [has_add M] {β : Sort u_2} {c : add_con M} (q : c.quotient) (f : M → β) :
(∀ (a b : M), c a bf a = f b) → β

The function on the quotient by a congruence relation c induced by a function that is constant on c's equivalence classes.

def add_con.lift_on₂ {M : Type u_1} [has_add M] {β : Sort u_2} {c : add_con M} (q r : c.quotient) (f : M → M → β) :
(∀ (a₁ a₂ b₁ b₂ : M), c a₁ b₁c a₂ b₂f a₁ a₂ = f b₁ b₂) → β

The binary function on the quotient by a congruence relation c induced by a binary function that is constant on c's equivalence classes.

def con.lift_on₂ {M : Type u_1} [has_mul M] {β : Sort u_2} {c : con M} (q r : c.quotient) (f : M → M → β) :
(∀ (a₁ a₂ b₁ b₂ : M), c a₁ b₁c a₂ b₂f a₁ a₂ = f b₁ b₂) → β

The binary function on the quotient by a congruence relation c induced by a binary function that is constant on c's equivalence classes.

Equations
theorem add_con.induction_on {M : Type u_1} [has_add M] {c : add_con M} {C : c.quotient → Prop} (q : c.quotient) :
(∀ (x : M), C x)C q

The inductive principle used to prove propositions about the elements of a quotient by an additive congruence relation.

theorem con.induction_on {M : Type u_1} [has_mul M] {c : con M} {C : c.quotient → Prop} (q : c.quotient) :
(∀ (x : M), C x)C q

The inductive principle used to prove propositions about the elements of a quotient by a congruence relation.

theorem con.induction_on₂ {M : Type u_1} {N : Type u_2} [has_mul M] [has_mul N] {c : con M} {d : con N} {C : c.quotientd.quotient → Prop} (p : c.quotient) (q : d.quotient) :
(∀ (x : M) (y : N), C x y)C p q

A version of con.induction_on for predicates which take two arguments.

theorem add_con.induction_on₂ {M : Type u_1} {N : Type u_2} [has_add M] [has_add N] {c : add_con M} {d : add_con N} {C : c.quotientd.quotient → Prop} (p : c.quotient) (q : d.quotient) :
(∀ (x : M) (y : N), C x y)C p q

A version of add_con.induction_on for predicates which take two arguments.

@[simp]
theorem con.eq {M : Type u_1} [has_mul M] (c : con M) {a b : M} :
a = b c a b

Two elements are related by a congruence relation c iff they are represented by the same element of the quotient by c.

@[simp]
theorem add_con.eq {M : Type u_1} [has_add M] (c : add_con M) {a b : M} :
a = b c a b

Two elements are related by an additive congruence relation c iff they are represented by the same element of the quotient by c.

@[instance]
def con.has_mul {M : Type u_1} [has_mul M] (c : con M) :

The multiplication induced on the quotient by a congruence relation on a type with a multiplication.

Equations
@[instance]
def add_con.has_add {M : Type u_1} [has_add M] (c : add_con M) :

The addition induced on the quotient by an additive congruence relation on a type with an addition.

@[simp]
theorem con.mul_ker_mk_eq {M : Type u_1} [has_mul M] (c : con M) :

The kernel of the quotient map induced by a congruence relation c equals c.

@[simp]
theorem add_con.add_ker_mk_eq {M : Type u_1} [has_add M] (c : add_con M) :

The kernel of the quotient map induced by an additive congruence relation c equals c.

@[simp]
theorem con.coe_mul {M : Type u_1} [has_mul M] {c : con M} (x y : M) :
x * y = (x) * y

The coercion to the quotient of a congruence relation commutes with multiplication (by definition).

@[simp]
theorem add_con.coe_add {M : Type u_1} [has_add M] {c : add_con M} (x y : M) :
(x + y) = x + y

The coercion to the quotient of an additive congruence relation commutes with addition (by definition).

@[simp]
theorem add_con.lift_on_beta {M : Type u_1} [has_add M] {β : Sort u_2} (c : add_con M) (f : M → β) (h : ∀ (a b : M), c a bf a = f b) (x : M) :

Definition of the function on the quotient by an additive congruence relation c induced by a function that is constant on c's equivalence classes.

@[simp]
theorem con.lift_on_beta {M : Type u_1} [has_mul M] {β : Sort u_2} (c : con M) (f : M → β) (h : ∀ (a b : M), c a bf a = f b) (x : M) :
con.lift_on x f h = f x

Definition of the function on the quotient by a congruence relation c induced by a function that is constant on c's equivalence classes.

def add_con.congr {M : Type u_1} [has_add M] {c d : add_con M} :
c = dc.quotient ≃+ d.quotient

Makes an additive isomorphism of quotients by two additive congruence relations, given that the relations are equal.

def con.congr {M : Type u_1} [has_mul M] {c d : con M} :
c = dc.quotient ≃* d.quotient

Makes an isomorphism of quotients by two congruence relations, given that the relations are equal.

Equations
@[instance]
def con.has_le {M : Type u_1} [has_mul M] :

For congruence relations c, d on a type M with a multiplication, c ≤ d iff ∀ x y ∈ M, x is related to y by d if x is related to y by c.

Equations
@[instance]
def add_con.has_le {M : Type u_1} [has_add M] :

For additive congruence relations c, d on a type M with an addition, c ≤ d iff ∀ x y ∈ M, x is related to y by d if x is related to y by c.

theorem con.le_def {M : Type u_1} [has_mul M] {c d : con M} :
c d ∀ {x y : M}, c x yd x y

Definition of for congruence relations.

theorem add_con.le_def {M : Type u_1} [has_add M] {c d : add_con M} :
c d ∀ {x y : M}, c x yd x y

Definition of for additive congruence relations.

@[instance]
def add_con.has_Inf {M : Type u_1} [has_add M] :

The infimum of a set of additive congruence relations on a given type with an addition.

@[instance]
def con.has_Inf {M : Type u_1} [has_mul M] :

The infimum of a set of congruence relations on a given type with a multiplication.

Equations
theorem add_con.Inf_to_setoid {M : Type u_1} [has_add M] (S : set (add_con M)) :

The infimum of a set of additive congruence relations is the same as the infimum of the set's image under the map to the underlying equivalence relation.

theorem con.Inf_to_setoid {M : Type u_1} [has_mul M] (S : set (con M)) :

The infimum of a set of congruence relations is the same as the infimum of the set's image under the map to the underlying equivalence relation.

theorem add_con.Inf_def {M : Type u_1} [has_add M] (S : set (add_con M)) :
(Inf S).r = Inf (add_con.r '' S)

The infimum of a set of additive congruence relations is the same as the infimum of the set's image under the map to the underlying binary relation.

theorem con.Inf_def {M : Type u_1} [has_mul M] (S : set (con M)) :
(Inf S).r = Inf (con.r '' S)

The infimum of a set of congruence relations is the same as the infimum of the set's image under the map to the underlying binary relation.

@[instance]
def add_con.partial_order {M : Type u_1} [has_add M] :

@[instance]
def con.partial_order {M : Type u_1} [has_mul M] :

Equations
@[instance]
def con.complete_lattice {M : Type u_1} [has_mul M] :

The complete lattice of congruence relations on a given type with a multiplication.

Equations
@[instance]

The complete lattice of additive congruence relations on a given type with an addition.

theorem con.inf_def {M : Type u_1} [has_mul M] {c d : con M} :
(c d).r = c.r d.r

The infimum of two congruence relations equals the infimum of the underlying binary operations.

theorem add_con.inf_def {M : Type u_1} [has_add M] {c d : add_con M} :
(c d).r = c.r d.r

The infimum of two additive congruence relations equals the infimum of the underlying binary operations.

theorem con.inf_iff_and {M : Type u_1} [has_mul M] {c d : con M} {x y : M} :
(c d) x y c x y d x y

Definition of the infimum of two congruence relations.

theorem add_con.inf_iff_and {M : Type u_1} [has_add M] {c d : add_con M} {x y : M} :
(c d) x y c x y d x y

Definition of the infimum of two additive congruence relations.

theorem add_con.add_con_gen_eq {M : Type u_1} [has_add M] (r : M → M → Prop) :
add_con_gen r = Inf {s : add_con M | ∀ (x y : M), r x ys x y}

The inductively defined smallest additive congruence relation containing a binary relation r equals the infimum of the set of additive congruence relations containing r.

theorem con.con_gen_eq {M : Type u_1} [has_mul M] (r : M → M → Prop) :
con_gen r = Inf {s : con M | ∀ (x y : M), r x ys x y}

The inductively defined smallest congruence relation containing a binary relation r equals the infimum of the set of congruence relations containing r.

theorem con.con_gen_le {M : Type u_1} [has_mul M] {r : M → M → Prop} {c : con M} :
(∀ (x y : M), r x yc.r x y)con_gen r c

The smallest congruence relation containing a binary relation r is contained in any congruence relation containing r.

theorem add_con.add_con_gen_le {M : Type u_1} [has_add M] {r : M → M → Prop} {c : add_con M} :
(∀ (x y : M), r x yc.r x y)add_con_gen r c

The smallest additive congruence relation containing a binary relation r is contained in any additive congruence relation containing r.

theorem add_con.add_con_gen_mono {M : Type u_1} [has_add M] {r s : M → M → Prop} :
(∀ (x y : M), r x ys x y)add_con_gen r add_con_gen s

Given binary relations r, s with r contained in s, the smallest additive congruence relation containing s contains the smallest additive congruence relation containing r.

theorem con.con_gen_mono {M : Type u_1} [has_mul M] {r s : M → M → Prop} :
(∀ (x y : M), r x ys x y)con_gen r con_gen s

Given binary relations r, s with r contained in s, the smallest congruence relation containing s contains the smallest congruence relation containing r.

@[simp]
theorem add_con.add_con_gen_of_add_con {M : Type u_1} [has_add M] (c : add_con M) :

Additive congruence relations equal the smallest additive congruence relation in which they are contained.

@[simp]
theorem con.con_gen_of_con {M : Type u_1} [has_mul M] (c : con M) :

Congruence relations equal the smallest congruence relation in which they are contained.

@[simp]
theorem add_con.add_con_gen_idem {M : Type u_1} [has_add M] (r : M → M → Prop) :

The map sending a binary relation to the smallest additive congruence relation in which it is contained is idempotent.

@[simp]
theorem con.con_gen_idem {M : Type u_1} [has_mul M] (r : M → M → Prop) :

The map sending a binary relation to the smallest congruence relation in which it is contained is idempotent.

theorem add_con.sup_eq_add_con_gen {M : Type u_1} [has_add M] (c d : add_con M) :
c d = add_con_gen (λ (x y : M), c x y d x y)

The supremum of additive congruence relations c, d equals the smallest additive congruence relation containing the binary relation 'x is related to y by c or d'.

theorem con.sup_eq_con_gen {M : Type u_1} [has_mul M] (c d : con M) :
c d = con_gen (λ (x y : M), c x y d x y)

The supremum of congruence relations c, d equals the smallest congruence relation containing the binary relation 'x is related to y by c or d'.

theorem con.sup_def {M : Type u_1} [has_mul M] {c d : con M} :
c d = con_gen (c.r d.r)

The supremum of two congruence relations equals the smallest congruence relation containing the supremum of the underlying binary operations.

theorem add_con.sup_def {M : Type u_1} [has_add M] {c d : add_con M} :
c d = add_con_gen (c.r d.r)

The supremum of two additive congruence relations equals the smallest additive congruence relation containing the supremum of the underlying binary operations.

theorem con.Sup_eq_con_gen {M : Type u_1} [has_mul M] (S : set (con M)) :
Sup S = con_gen (λ (x y : M), ∃ (c : con M), c S c x y)

The supremum of a set of congruence relations S equals the smallest congruence relation containing the binary relation 'there exists c ∈ S such that x is related to y by c'.

theorem add_con.Sup_eq_add_con_gen {M : Type u_1} [has_add M] (S : set (add_con M)) :
Sup S = add_con_gen (λ (x y : M), ∃ (c : add_con M), c S c x y)

The supremum of a set of additive congruence relations S equals the smallest additive congruence relation containing the binary relation 'there exists c ∈ S such that x is related to y by c'.

theorem add_con.Sup_def {M : Type u_1} [has_add M] {S : set (add_con M)} :

The supremum of a set of additive congruence relations is the same as the smallest additive congruence relation containing the supremum of the set's image under the map to the underlying binary relation.

theorem con.Sup_def {M : Type u_1} [has_mul M] {S : set (con M)} :

The supremum of a set of congruence relations is the same as the smallest congruence relation containing the supremum of the set's image under the map to the underlying binary relation.

def con.gi (M : Type u_1) [has_mul M] :

There is a Galois insertion of congruence relations on a type with a multiplication M into binary relations on M.

Equations

There is a Galois insertion of additive congruence relations on a type with an addition M into binary relations on M.

def add_con.map_gen {M : Type u_1} {N : Type u_2} [has_add M] [has_add N] :
add_con M(M → N)add_con N

Given a function f, the smallest additive congruence relation containing the binary relation on f's image defined by 'x ≈ y iff the elements of f⁻¹(x) are related to the elements of f⁻¹(y) by an additive congruence relation c.'

def con.map_gen {M : Type u_1} {N : Type u_2} [has_mul M] [has_mul N] :
con M(M → N)con N

Given a function f, the smallest congruence relation containing the binary relation on f's image defined by 'x ≈ y iff the elements of f⁻¹(x) are related to the elements of f⁻¹(y) by a congruence relation c.'

Equations
def con.map_of_surjective {M : Type u_1} {N : Type u_2} [has_mul M] [has_mul N] (c : con M) (f : M → N) (H : ∀ (x y : M), f (x * y) = (f x) * f y) :

Given a surjective multiplicative-preserving function f whose kernel is contained in a congruence relation c, the congruence relation on f's codomain defined by 'x ≈ y iff the elements of f⁻¹(x) are related to the elements of f⁻¹(y) by c.'

Equations
def add_con.map_of_surjective {M : Type u_1} {N : Type u_2} [has_add M] [has_add N] (c : add_con M) (f : M → N) (H : ∀ (x y : M), f (x + y) = f x + f y) :

Given a surjective addition-preserving function f whose kernel is contained in an additive congruence relation c, the additive congruence relation on f's codomain defined by 'x ≈ y iff the elements of f⁻¹(x) are related to the elements of f⁻¹(y) by c.'

theorem add_con.map_of_surjective_eq_map_gen {M : Type u_1} {N : Type u_2} [has_add M] [has_add N] {c : add_con M} {f : M → N} (H : ∀ (x y : M), f (x + y) = f x + f y) (h : add_con.add_ker f H c) (hf : function.surjective f) :
c.map_gen f = c.map_of_surjective f H h hf

A specialization of 'the smallest additive congruence relation containing an additive congruence relation c equals c'.

theorem con.map_of_surjective_eq_map_gen {M : Type u_1} {N : Type u_2} [has_mul M] [has_mul N] {c : con M} {f : M → N} (H : ∀ (x y : M), f (x * y) = (f x) * f y) (h : con.mul_ker f H c) (hf : function.surjective f) :
c.map_gen f = c.map_of_surjective f H h hf

A specialization of 'the smallest congruence relation containing a congruence relation c equals c'.

def con.comap {M : Type u_1} {N : Type u_2} [has_mul M] [has_mul N] (f : M → N) :
(∀ (x y : M), f (x * y) = (f x) * f y)con Ncon M

Given types with multiplications M, N and a congruence relation c on N, a multiplication-preserving map f : M → N induces a congruence relation on f's domain defined by 'x ≈ y iff f(x) is related to f(y) by c.'

Equations
def add_con.comap {M : Type u_1} {N : Type u_2} [has_add M] [has_add N] (f : M → N) :
(∀ (x y : M), f (x + y) = f x + f y)add_con Nadd_con M

Given types with additions M, N and an additive congruence relation c on N, an addition-preserving map f : M → N induces an additive congruence relation on f's domain defined by 'x ≈ y iff f(x) is related to f(y) by c.'

def con.correspondence {M : Type u_1} [has_mul M] (c : con M) :
{d // c d} ≃o con c.quotient

Given a congruence relation c on a type M with a multiplication, the order-preserving bijection between the set of congruence relations containing c and the congruence relations on the quotient of M by c.

Equations
def add_con.correspondence {M : Type u_1} [has_add M] (c : add_con M) :
{d // c d} ≃o add_con c.quotient

Given an additive congruence relation c on a type M with an addition, the order-preserving bijection between the set of additive congruence relations containing c and the additive congruence relations on the quotient of M by c.

@[instance]
def con.monoid {M : Type u_1} [monoid M] (c : con M) :

The quotient of a monoid by a congruence relation is a monoid.

Equations
@[instance]
def add_con.add_monoid {M : Type u_1} [add_monoid M] (c : add_con M) :

The quotient of an add_monoid by an additive congruence relation is an add_monoid.

@[instance]

The quotient of an add_comm_monoid by an additive congruence relation is an add_comm_monoid.

@[instance]
def con.comm_monoid {α : Type u_1} [comm_monoid α] (c : con α) :

The quotient of a comm_monoid by a congruence relation is a comm_monoid.

Equations
@[simp]
theorem con.coe_one {M : Type u_1} [monoid M] {c : con M} :
1 = 1

The 1 of the quotient of a monoid by a congruence relation is the equivalence class of the monoid's 1.

@[simp]
theorem add_con.coe_zero {M : Type u_1} [add_monoid M] {c : add_con M} :
0 = 0

The 0 of the quotient of an add_monoid by an additive congruence relation is the equivalence class of the add_monoid's 0.

def con.submonoid (M : Type u_1) [monoid M] :
con Msubmonoid (M × M)

The submonoid of M × M defined by a congruence relation on a monoid M.

Equations
def add_con.add_submonoid (M : Type u_1) [add_monoid M] :

The add_submonoid of M × M defined by an additive congruence relation on an add_monoid M.

def con.of_submonoid {M : Type u_1} [monoid M] (N : submonoid (M × M)) :
equivalence (λ (x y : M), (x, y) N)con M

The congruence relation on a monoid M from a submonoid of M × M for which membership is an equivalence relation.

Equations
def add_con.of_add_submonoid {M : Type u_1} [add_monoid M] (N : add_submonoid (M × M)) :
equivalence (λ (x y : M), (x, y) N)add_con M

The additive congruence relation on an add_monoid M from an add_submonoid of M × M for which membership is an equivalence relation.

@[instance]
def con.to_submonoid {M : Type u_1} [monoid M] :
has_coe (con M) (submonoid (M × M))

Coercion from a congruence relation c on a monoid M to the submonoid of M × M whose elements are (x, y) such that x is related to y by c.

Equations
@[instance]
def add_con.to_add_submonoid {M : Type u_1} [add_monoid M] :

Coercion from a congruence relation c on an add_monoid M to the add_submonoid of M × M whose elements are (x, y) such that x is related to y by c.

theorem con.mem_coe {M : Type u_1} [monoid M] {c : con M} {x y : M} :
(x, y) c (x, y) c

theorem add_con.mem_coe {M : Type u_1} [add_monoid M] {c : add_con M} {x y : M} :
(x, y) c (x, y) c

theorem add_con.to_add_submonoid_inj {M : Type u_1} [add_monoid M] (c d : add_con M) :
c = dc = d

theorem con.to_submonoid_inj {M : Type u_1} [monoid M] (c d : con M) :
c = dc = d

theorem add_con.le_iff {M : Type u_1} [add_monoid M] {c d : add_con M} :
c d c d

theorem con.le_iff {M : Type u_1} [monoid M] {c d : con M} :
c d c d

def con.ker {M : Type u_1} {P : Type u_3} [monoid M] [monoid P] :
(M →* P)con M

The kernel of a monoid homomorphism as a congruence relation.

Equations
def add_con.ker {M : Type u_1} {P : Type u_3} [add_monoid M] [add_monoid P] :
(M →+ P)add_con M

The kernel of an add_monoid homomorphism as an additive congruence relation.

theorem con.ker_rel {M : Type u_1} {P : Type u_3} [monoid M] [monoid P] (f : M →* P) {x y : M} :
(con.ker f) x y f x = f y

The definition of the congruence relation defined by a monoid homomorphism's kernel.

theorem add_con.ker_rel {M : Type u_1} {P : Type u_3} [add_monoid M] [add_monoid P] (f : M →+ P) {x y : M} :
(add_con.ker f) x y f x = f y

The definition of the additive congruence relation defined by an add_monoid homomorphism's kernel.

@[instance]
def add_con.quotient.inhabited {M : Type u_1} [add_monoid M] {c : add_con M} :

There exists an element of the quotient of an add_monoid by a congruence relation (namely 0).

@[instance]
def con.quotient.inhabited {M : Type u_1} [monoid M] {c : con M} :

There exists an element of the quotient of a monoid by a congruence relation (namely 1).

Equations
def con.mk' {M : Type u_1} [monoid M] (c : con M) :

The natural homomorphism from a monoid to its quotient by a congruence relation.

Equations
def add_con.mk' {M : Type u_1} [add_monoid M] (c : add_con M) :

The natural homomorphism from an add_monoid to its quotient by an additive congruence relation.

@[simp]
theorem con.mk'_ker {M : Type u_1} [monoid M] (c : con M) :

The kernel of the natural homomorphism from a monoid to its quotient by a congruence relation c equals c.

@[simp]
theorem add_con.mk'_ker {M : Type u_1} [add_monoid M] (c : add_con M) :

The kernel of the natural homomorphism from an add_monoid to its quotient by an additive congruence relation c equals c.

theorem con.mk'_surjective {M : Type u_1} [monoid M] {c : con M} :

The natural homomorphism from a monoid to its quotient by a congruence relation is surjective.

theorem add_con.mk'_surjective {M : Type u_1} [add_monoid M] {c : add_con M} :

The natural homomorphism from an add_monoid to its quotient by a congruence relation is surjective.

@[simp]
theorem add_con.comp_mk'_apply {M : Type u_1} {P : Type u_3} [add_monoid M] [add_monoid P] {c : add_con M} (g : c.quotient →+ P) {x : M} :
(g.comp c.mk') x = g x

@[simp]
theorem con.comp_mk'_apply {M : Type u_1} {P : Type u_3} [monoid M] [monoid P] {c : con M} (g : c.quotient →* P) {x : M} :
(g.comp c.mk') x = g x

theorem add_con.ker_apply_eq_preimage {M : Type u_1} {P : Type u_3} [add_monoid M] [add_monoid P] {f : M →+ P} (x : M) :

The elements related to x ∈ M, M an add_monoid, by the kernel of an add_monoid homomorphism are those in the preimage of f(x) under f.

theorem con.ker_apply_eq_preimage {M : Type u_1} {P : Type u_3} [monoid M] [monoid P] {f : M →* P} (x : M) :
(con.ker f) x = f ⁻¹' {f x}

The elements related to x ∈ M, M a monoid, by the kernel of a monoid homomorphism are those in the preimage of f(x) under f.

theorem con.comap_eq {M : Type u_1} {N : Type u_2} [monoid M] [monoid N] {c : con M} {f : N →* M} :

Given a monoid homomorphism f : N → M and a congruence relation c on M, the congruence relation induced on N by f equals the kernel of c's quotient homomorphism composed with f.

theorem add_con.comap_eq {M : Type u_1} {N : Type u_2} [add_monoid M] [add_monoid N] {c : add_con M} {f : N →+ M} :

Given an add_monoid homomorphism f : N → M and an additive congruence relation c on M, the additive congruence relation induced on N by f equals the kernel of c's quotient homomorphism composed with f.

def con.lift {M : Type u_1} {P : Type u_3} [monoid M] [monoid P] (c : con M) (f : M →* P) :
c con.ker fc.quotient →* P

The homomorphism on the quotient of a monoid by a congruence relation c induced by a homomorphism constant on c's equivalence classes.

Equations
def add_con.lift {M : Type u_1} {P : Type u_3} [add_monoid M] [add_monoid P] (c : add_con M) (f : M →+ P) :

The homomorphism on the quotient of an add_monoid by an additive congruence relation c induced by a homomorphism constant on c's equivalence classes.

@[simp]
theorem add_con.lift_mk' {M : Type u_1} {P : Type u_3} [add_monoid M] [add_monoid P] {c : add_con M} {f : M →+ P} (H : c add_con.ker f) (x : M) :
(c.lift f H) ((c.mk') x) = f x

The diagram describing the universal property for quotients of add_monoids commutes.

@[simp]
theorem con.lift_mk' {M : Type u_1} {P : Type u_3} [monoid M] [monoid P] {c : con M} {f : M →* P} (H : c con.ker f) (x : M) :
(c.lift f H) ((c.mk') x) = f x

The diagram describing the universal property for quotients of monoids commutes.

@[simp]
theorem con.lift_coe {M : Type u_1} {P : Type u_3} [monoid M] [monoid P] {c : con M} {f : M →* P} (H : c con.ker f) (x : M) :
(c.lift f H) x = f x

The diagram describing the universal property for quotients of monoids commutes.

@[simp]
theorem add_con.lift_coe {M : Type u_1} {P : Type u_3} [add_monoid M] [add_monoid P] {c : add_con M} {f : M →+ P} (H : c add_con.ker f) (x : M) :
(c.lift f H) x = f x

The diagram describing the universal property for quotients of add_monoids commutes.

@[simp]
theorem con.lift_comp_mk' {M : Type u_1} {P : Type u_3} [monoid M] [monoid P] {c : con M} {f : M →* P} (H : c con.ker f) :
(c.lift f H).comp c.mk' = f

The diagram describing the universal property for quotients of monoids commutes.

@[simp]
theorem add_con.lift_comp_mk' {M : Type u_1} {P : Type u_3} [add_monoid M] [add_monoid P] {c : add_con M} {f : M →+ P} (H : c add_con.ker f) :
(c.lift f H).comp c.mk' = f

The diagram describing the universal property for quotients of add_monoids commutes.

@[simp]
theorem add_con.lift_apply_mk' {M : Type u_1} {P : Type u_3} [add_monoid M] [add_monoid P] {c : add_con M} (f : c.quotient →+ P) :
c.lift (f.comp c.mk') _ = f

Given a homomorphism f from the quotient of an add_monoid by an additive congruence relation, f equals the homomorphism on the quotient induced by f composed with the natural map from the add_monoid to the quotient.

@[simp]
theorem con.lift_apply_mk' {M : Type u_1} {P : Type u_3} [monoid M] [monoid P] {c : con M} (f : c.quotient →* P) :
c.lift (f.comp c.mk') _ = f

Given a homomorphism f from the quotient of a monoid by a congruence relation, f equals the homomorphism on the quotient induced by f composed with the natural map from the monoid to the quotient.

theorem add_con.lift_funext {M : Type u_1} {P : Type u_3} [add_monoid M] [add_monoid P] {c : add_con M} (f g : c.quotient →+ P) :
(∀ (a : M), f a = g a)f = g

Homomorphisms on the quotient of an add_monoid by an additive congruence relation are equal if they are equal on elements that are coercions from the add_monoid.

theorem con.lift_funext {M : Type u_1} {P : Type u_3} [monoid M] [monoid P] {c : con M} (f g : c.quotient →* P) :
(∀ (a : M), f a = g a)f = g

Homomorphisms on the quotient of a monoid by a congruence relation are equal if they are equal on elements that are coercions from the monoid.

theorem add_con.lift_unique {M : Type u_1} {P : Type u_3} [add_monoid M] [add_monoid P] {c : add_con M} {f : M →+ P} (H : c add_con.ker f) (g : c.quotient →+ P) :
g.comp c.mk' = fg = c.lift f H

The uniqueness part of the universal property for quotients of add_monoids.

theorem con.lift_unique {M : Type u_1} {P : Type u_3} [monoid M] [monoid P] {c : con M} {f : M →* P} (H : c con.ker f) (g : c.quotient →* P) :
g.comp c.mk' = fg = c.lift f H

The uniqueness part of the universal property for quotients of monoids.

theorem add_con.lift_range {M : Type u_1} {P : Type u_3} [add_monoid M] [add_monoid P] {c : add_con M} {f : M →+ P} (H : c add_con.ker f) :
(c.lift f H).mrange = f.mrange

Given an additive congruence relation c on an add_monoid and a homomorphism f constant on c's equivalence classes, f has the same image as the homomorphism that f induces on the quotient.

theorem con.lift_range {M : Type u_1} {P : Type u_3} [monoid M] [monoid P] {c : con M} {f : M →* P} (H : c con.ker f) :
(c.lift f H).mrange = f.mrange

Given a congruence relation c on a monoid and a homomorphism f constant on c's equivalence classes, f has the same image as the homomorphism that f induces on the quotient.

theorem con.lift_surjective_of_surjective {M : Type u_1} {P : Type u_3} [monoid M] [monoid P] {c : con M} {f : M →* P} (h : c con.ker f) :

Surjective monoid homomorphisms constant on a congruence relation c's equivalence classes induce a surjective homomorphism on c's quotient.

theorem add_con.lift_surjective_of_surjective {M : Type u_1} {P : Type u_3} [add_monoid M] [add_monoid P] {c : add_con M} {f : M →+ P} (h : c add_con.ker f) :

Surjective add_monoid homomorphisms constant on an additive congruence relation c's equivalence classes induce a surjective homomorphism on c's quotient.

theorem con.ker_eq_lift_of_injective {M : Type u_1} {P : Type u_3} [monoid M] [monoid P] (c : con M) (f : M →* P) (H : c con.ker f) :

Given a monoid homomorphism f from M to P, the kernel of f is the unique congruence relation on M whose induced map from the quotient of M to P is injective.

theorem add_con.ker_eq_lift_of_injective {M : Type u_1} {P : Type u_3} [add_monoid M] [add_monoid P] (c : add_con M) (f : M →+ P) (H : c add_con.ker f) :

Given an add_monoid homomorphism f from M to P, the kernel of f is the unique additive congruence relation on M whose induced map from the quotient of M to P is injective.

def add_con.ker_lift {M : Type u_1} {P : Type u_3} [add_monoid M] [add_monoid P] (f : M →+ P) :

The homomorphism induced on the quotient of an add_monoid by the kernel of an add_monoid homomorphism.

def con.ker_lift {M : Type u_1} {P : Type u_3} [monoid M] [monoid P] (f : M →* P) :

The homomorphism induced on the quotient of a monoid by the kernel of a monoid homomorphism.

Equations
@[simp]
theorem con.ker_lift_mk {M : Type u_1} {P : Type u_3} [monoid M] [monoid P] {f : M →* P} (x : M) :

The diagram described by the universal property for quotients of monoids, when the congruence relation is the kernel of the homomorphism, commutes.

@[simp]
theorem add_con.ker_lift_mk {M : Type u_1} {P : Type u_3} [add_monoid M] [add_monoid P] {f : M →+ P} (x : M) :

The diagram described by the universal property for quotients of add_monoids, when the additive congruence relation is the kernel of the homomorphism, commutes.

@[simp]
theorem add_con.ker_lift_range_eq {M : Type u_1} {P : Type u_3} [add_monoid M] [add_monoid P] {f : M →+ P} :

Given an add_monoid homomorphism f, the induced homomorphism on the quotient by f's kernel has the same image as f.

@[simp]
theorem con.ker_lift_range_eq {M : Type u_1} {P : Type u_3} [monoid M] [monoid P] {f : M →* P} :

Given a monoid homomorphism f, the induced homomorphism on the quotient by f's kernel has the same image as f.

theorem con.ker_lift_injective {M : Type u_1} {P : Type u_3} [monoid M] [monoid P] (f : M →* P) :

A monoid homomorphism f induces an injective homomorphism on the quotient by f's kernel.

theorem add_con.ker_lift_injective {M : Type u_1} {P : Type u_3} [add_monoid M] [add_monoid P] (f : M →+ P) :

An add_monoid homomorphism f induces an injective homomorphism on the quotient by f's kernel.

def con.map {M : Type u_1} [monoid M] (c d : con M) :

Given congruence relations c, d on a monoid such that d contains c, d's quotient map induces a homomorphism from the quotient by c to the quotient by d.

Equations
def add_con.map {M : Type u_1} [add_monoid M] (c d : add_con M) :

Given additive congruence relations c, d on an add_monoid such that d contains c, d's quotient map induces a homomorphism from the quotient by c to the quotient by d.

theorem add_con.map_apply {M : Type u_1} [add_monoid M] {c d : add_con M} (h : c d) (x : c.quotient) :
(c.map d h) x = (c.lift d.mk' _) x

Given additive congruence relations c, d on an add_monoid such that d contains c, the definition of the homomorphism from the quotient by c to the quotient by d induced by d's quotient map.

theorem con.map_apply {M : Type u_1} [monoid M] {c d : con M} (h : c d) (x : c.quotient) :
(c.map d h) x = (c.lift d.mk' _) x

Given congruence relations c, d on a monoid such that d contains c, the definition of the homomorphism from the quotient by c to the quotient by d induced by d's quotient map.

def add_con.quotient_ker_equiv_range {M : Type u_1} {P : Type u_3} [add_monoid M] [add_monoid P] (f : M →+ P) :

The first isomorphism theorem for add_monoids.

def add_con.quotient_ker_equiv_of_surjective {M : Type u_1} {P : Type u_3} [add_monoid M] [add_monoid P] (f : M →+ P) :

The first isomorphism theorem for add_monoids in the case of a surjective homomorphism.

def con.quotient_ker_equiv_of_surjective {M : Type u_1} {P : Type u_3} [monoid M] [monoid P] (f : M →* P) :

The first isomorphism theorem for monoids in the case of a surjective homomorphism.

Equations
def add_con.comap_quotient_equiv {M : Type u_1} {N : Type u_2} [add_monoid M] [add_monoid N] (c : add_con M) (f : N →+ M) :

The second isomorphism theorem for add_monoids.

def con.comap_quotient_equiv {M : Type u_1} {N : Type u_2} [monoid M] [monoid N] (c : con M) (f : N →* M) :

The second isomorphism theorem for monoids.

Equations
def con.quotient_quotient_equiv_quotient {M : Type u_1} [monoid M] (c d : con M) (h : c d) :

The third isomorphism theorem for monoids.

Equations
def add_con.quotient_quotient_equiv_quotient {M : Type u_1} [add_monoid M] (c d : add_con M) (h : c d) :

The third isomorphism theorem for add_monoids.