mathlib documentation

algebra.pointwise

Pointwise addition, multiplication, and scalar multiplication of sets.

This file defines pointwise algebraic operations on sets.

For a type α with multiplication, multiplication is defined on set α by taking s * t to be the set of all x * y where x ∈ s and y ∈ t. Similarly for addition.
For α a semigroup, set α is a semigroup.
If α is a (commutative) monoid, we define an alias set_semiring α for set α, which then becomes a (commutative) semiring with union as addition and pointwise multiplication as multiplication.
For a type β with scalar multiplication by another type α, this file defines a scalar multiplication of set β by set α and a separate scalar multiplication of set β by α.
We also define pointwise multiplication on finset.

Appropriate definitions and results are also transported to the additive theory via to_additive.

Implementation notes

The following expressions are considered in simp-normal form in a group: (λ h, h * g) ⁻¹' s, (λ h, g * h) ⁻¹' s, (λ h, h * g⁻¹) ⁻¹' s, (λ h, g⁻¹ * h) ⁻¹' s, s * t, s⁻¹, (1 : set _) (and similarly for additive variants). Expressions equal to one of these will be simplified.

Tags

set multiplication, set addition, pointwise addition, pointwise multiplication

Properties about 1

@[instance]

def set.has_one {α : Type u_1} [has_one α] :

has_one (set α)

Equations

set.has_one = {one := {1}}

@[instance]

def set.has_zero {α : Type u_1} [has_zero α] :

has_zero (set α)

@[simp]

theorem set.singleton_one {α : Type u_1} [has_one α] :

{1} = 1

@[simp]

theorem set.singleton_zero {α : Type u_1} [has_zero α] :

{0} = 0

@[simp]

theorem set.mem_one {α : Type u_1} {a : α} [has_one α] :

a ∈ 1 ↔ a = 1

@[simp]

theorem set.mem_zero {α : Type u_1} {a : α} [has_zero α] :

a ∈ 0 ↔ a = 0

theorem set.zero_mem_zero {α : Type u_1} [has_zero α] :

0 ∈ 0

theorem set.one_mem_one {α : Type u_1} [has_one α] :

1 ∈ 1

@[simp]

theorem set.zero_subset {α : Type u_1} {s : set α} [has_zero α] :

0 ⊆ s ↔ 0 ∈ s

@[simp]

theorem set.one_subset {α : Type u_1} {s : set α} [has_one α] :

1 ⊆ s ↔ 1 ∈ s

theorem set.zero_nonempty {α : Type u_1} [has_zero α] :

theorem set.one_nonempty {α : Type u_1} [has_one α] :

@[simp]

theorem set.image_zero {α : Type u_1} {β : Type u_2} [has_zero α] {f : α → β} :

f '' 0 = {f 0}

@[simp]

theorem set.image_one {α : Type u_1} {β : Type u_2} [has_one α] {f : α → β} :

f '' 1 = {f 1}

Properties about multiplication

@[instance]

def set.has_mul {α : Type u_1} [has_mul α] :

has_mul (set α)

Equations

set.has_mul = {mul := set.image2 has_mul.mul}

@[instance]

def set.has_add {α : Type u_1} [has_add α] :

has_add (set α)

@[simp]

theorem set.image2_mul {α : Type u_1} {s t : set α} [has_mul α] :

set.image2 has_mul.mul s t = s * t

@[simp]

theorem set.image2_add {α : Type u_1} {s t : set α} [has_add α] :

set.image2 has_add.add s t = s + t

theorem set.mem_add {α : Type u_1} {s t : set α} {a : α} [has_add α] :

a ∈ s + t ↔ ∃ (x y : α), x ∈ s ∧ y ∈ t ∧ x + y = a

theorem set.mem_mul {α : Type u_1} {s t : set α} {a : α} [has_mul α] :

a ∈ s * t ↔ ∃ (x y : α), x ∈ s ∧ y ∈ t ∧ x * y = a

theorem set.mul_mem_mul {α : Type u_1} {s t : set α} {a b : α} [has_mul α] (ha : a ∈ s) (hb : b ∈ t) :

a * b ∈ s * t

theorem set.add_mem_add {α : Type u_1} {s t : set α} {a b : α} [has_add α] (ha : a ∈ s) (hb : b ∈ t) :

a + b ∈ s + t

theorem set.image_mul_prod {α : Type u_1} {s t : set α} [has_mul α] :

(λ (x : α × α), (x.fst) * x.snd) '' s.prod t = s * t

theorem set.add_image_prod {α : Type u_1} {s t : set α} [has_add α] :

(λ (x : α × α), x.fst + x.snd) '' s.prod t = s + t

@[simp]

theorem set.image_add_left {α : Type u_1} {t : set α} {a : α} [add_group α] :

(λ (b : α), a + b) '' t = (λ (b : α), -a + b) ⁻¹' t

@[simp]

theorem set.image_mul_left {α : Type u_1} {t : set α} {a : α} [group α] :

(λ (b : α), a * b) '' t = (λ (b : α), a⁻¹ * b) ⁻¹' t

@[simp]

theorem set.image_mul_right {α : Type u_1} {t : set α} {b : α} [group α] :

(λ (a : α), a * b) '' t = (λ (a : α), a * b⁻¹) ⁻¹' t

@[simp]

theorem set.image_add_right {α : Type u_1} {t : set α} {b : α} [add_group α] :

(λ (a : α), a + b) '' t = (λ (a : α), a + -b) ⁻¹' t

theorem set.image_mul_left' {α : Type u_1} {t : set α} {a : α} [group α] :

(λ (b : α), a⁻¹ * b) '' t = (λ (b : α), a * b) ⁻¹' t

theorem set.image_add_left' {α : Type u_1} {t : set α} {a : α} [add_group α] :

(λ (b : α), -a + b) '' t = (λ (b : α), a + b) ⁻¹' t

theorem set.image_mul_right' {α : Type u_1} {t : set α} {b : α} [group α] :

(λ (a : α), a * b⁻¹) '' t = (λ (a : α), a * b) ⁻¹' t

theorem set.image_add_right' {α : Type u_1} {t : set α} {b : α} [add_group α] :

(λ (a : α), a + -b) '' t = (λ (a : α), a + b) ⁻¹' t

@[simp]

theorem set.preimage_mul_left_one {α : Type u_1} {a : α} [group α] :

(λ (b : α), a * b) ⁻¹' 1 = {a⁻¹}

@[simp]

theorem set.preimage_add_left_zero {α : Type u_1} {a : α} [add_group α] :

(λ (b : α), a + b) ⁻¹' 0 = {-a}

@[simp]

theorem set.preimage_add_right_zero {α : Type u_1} {b : α} [add_group α] :

(λ (a : α), a + b) ⁻¹' 0 = {-b}

@[simp]

theorem set.preimage_mul_right_one {α : Type u_1} {b : α} [group α] :

(λ (a : α), a * b) ⁻¹' 1 = {b⁻¹}

theorem set.preimage_add_left_zero' {α : Type u_1} {a : α} [add_group α] :

(λ (b : α), -a + b) ⁻¹' 0 = {a}

theorem set.preimage_mul_left_one' {α : Type u_1} {a : α} [group α] :

(λ (b : α), a⁻¹ * b) ⁻¹' 1 = {a}

theorem set.preimage_add_right_zero' {α : Type u_1} {b : α} [add_group α] :

(λ (a : α), a + -b) ⁻¹' 0 = {b}

theorem set.preimage_mul_right_one' {α : Type u_1} {b : α} [group α] :

(λ (a : α), a * b⁻¹) ⁻¹' 1 = {b}

@[simp]

theorem set.add_singleton {α : Type u_1} {s : set α} {b : α} [has_add α] :

s + {b} = (λ (a : α), a + b) '' s

@[simp]

theorem set.mul_singleton {α : Type u_1} {s : set α} {b : α} [has_mul α] :

s * {b} = (λ (a : α), a * b) '' s

@[simp]

theorem set.singleton_add {α : Type u_1} {t : set α} {a : α} [has_add α] :

{a} + t = (λ (b : α), a + b) '' t

@[simp]

theorem set.singleton_mul {α : Type u_1} {t : set α} {a : α} [has_mul α] :

{a} * t = (λ (b : α), a * b) '' t

@[simp]

theorem set.singleton_mul_singleton {α : Type u_1} {a b : α} [has_mul α] :

{a} * {b} = {a * b}

@[simp]

theorem set.singleton_add_singleton {α : Type u_1} {a b : α} [has_add α] :

{a} + {b} = {a + b}

@[instance]

def set.add_semigroup {α : Type u_1} [add_semigroup α] :

add_semigroup (set α)

@[instance]

def set.semigroup {α : Type u_1} [semigroup α] :

semigroup (set α)

Equations

set.semigroup = {mul := has_mul.mul set.has_mul, mul_assoc := _}

@[instance]

def set.monoid {α : Type u_1} [monoid α] :

monoid (set α)

Equations

set.monoid = {mul := semigroup.mul set.semigroup, mul_assoc := _, one := 1, one_mul := _, mul_one := _}

@[instance]

def set.add_monoid {α : Type u_1} [add_monoid α] :

add_monoid (set α)

theorem set.mul_comm {α : Type u_1} {s t : set α} [comm_semigroup α] :

s * t = t * s

theorem set.add_comm {α : Type u_1} {s t : set α} [add_comm_semigroup α] :

s + t = t + s

@[instance]

def set.comm_monoid {α : Type u_1} [comm_monoid α] :

comm_monoid (set α)

Equations

set.comm_monoid = {mul := monoid.mul set.monoid, mul_assoc := _, one := monoid.one set.monoid, one_mul := _, mul_one := _, mul_comm := _}

@[instance]

def set.add_comm_monoid {α : Type u_1} [add_comm_monoid α] :

add_comm_monoid (set α)

theorem set.singleton.is_mul_hom {α : Type u_1} [has_mul α] :

is_mul_hom singleton

theorem set.singleton.is_add_hom {α : Type u_1} [has_add α] :

is_add_hom singleton

@[simp]

theorem set.empty_mul {α : Type u_1} {s : set α} [has_mul α] :

@[simp]

theorem set.empty_add {α : Type u_1} {s : set α} [has_add α] :

@[simp]

theorem set.add_empty {α : Type u_1} {s : set α} [has_add α] :

@[simp]

theorem set.mul_empty {α : Type u_1} {s : set α} [has_mul α] :

theorem set.add_subset_add {α : Type u_1} {s₁ s₂ t₁ t₂ : set α} [has_add α] (h₁ : s₁ ⊆ t₁) (h₂ : s₂ ⊆ t₂) :

s₁ + s₂ ⊆ t₁ + t₂

theorem set.mul_subset_mul {α : Type u_1} {s₁ s₂ t₁ t₂ : set α} [has_mul α] (h₁ : s₁ ⊆ t₁) (h₂ : s₂ ⊆ t₂) :

s₁ * s₂ ⊆ t₁ * t₂

theorem set.union_mul {α : Type u_1} {s t u : set α} [has_mul α] :

(s ∪ t) * u = s * u ∪ t * u

theorem set.union_add {α : Type u_1} {s t u : set α} [has_add α] :

s ∪ t + u = s + u ∪ (t + u)

theorem set.mul_union {α : Type u_1} {s t u : set α} [has_mul α] :

s * (t ∪ u) = s * t ∪ s * u

theorem set.add_union {α : Type u_1} {s t u : set α} [has_add α] :

s + (t ∪ u) = s + t ∪ (s + u)

theorem set.Union_mul_left_image {α : Type u_1} {s t : set α} [has_mul α] :

(⋃ (a : α) (H : a ∈ s), (λ (x : α), a * x) '' t) = s * t

theorem set.Union_add_left_image {α : Type u_1} {s t : set α} [has_add α] :

(⋃ (a : α) (H : a ∈ s), (λ (x : α), a + x) '' t) = s + t

theorem set.Union_mul_right_image {α : Type u_1} {s t : set α} [has_mul α] :

(⋃ (a : α) (H : a ∈ t), (λ (x : α), x * a) '' s) = s * t

theorem set.Union_add_right_image {α : Type u_1} {s t : set α} [has_add α] :

(⋃ (a : α) (H : a ∈ t), (λ (x : α), x + a) '' s) = s + t

@[simp]

theorem set.univ_add_univ {α : Type u_1} [add_monoid α] :

set.univ + set.univ = set.univ

@[simp]

theorem set.univ_mul_univ {α : Type u_1} [monoid α] :

set.univ * set.univ = set.univ

def set.singleton_hom {α : Type u_1} [monoid α] :

α →* set α

singleton is a monoid hom.

Equations

set.singleton_hom = {to_fun := singleton set.has_singleton, map_one' := _, map_mul' := _}

def set.singleton_add_hom {α : Type u_1} [add_monoid α] :

α →+ set α

singleton is an add monoid hom

theorem set.nonempty.add {α : Type u_1} {s t : set α} [has_add α] (a : s.nonempty) (a_1 : t.nonempty) :

(s + t).nonempty

theorem set.nonempty.mul {α : Type u_1} {s t : set α} [has_mul α] (a : s.nonempty) (a_1 : t.nonempty) :

(s * t).nonempty

theorem set.finite.mul {α : Type u_1} {s t : set α} [has_mul α] (hs : s.finite) (ht : t.finite) :

(s * t).finite

theorem set.finite.add {α : Type u_1} {s t : set α} [has_add α] (hs : s.finite) (ht : t.finite) :

(s + t).finite

def set.fintype_add {α : Type u_1} [has_add α] [decidable_eq α] (s t : set α) [hs : fintype ↥s] [ht : fintype ↥t] :

fintype ↥(s + t)

addition preserves finiteness

def set.fintype_mul {α : Type u_1} [has_mul α] [decidable_eq α] (s t : set α) [hs : fintype ↥s] [ht : fintype ↥t] :

fintype (↥s * t)

multiplication preserves finiteness

Equations

s.fintype_mul t = set.fintype_image2 (λ (a b : α), a * b) s t

Properties about inversion

@[instance]

def set.has_neg' {α : Type u_1} [has_neg α] :

has_neg (set α)

@[instance]

def set.has_inv {α : Type u_1} [has_inv α] :

has_inv (set α)

Equations

set.has_inv = {inv := set.preimage has_inv.inv}

@[simp]

theorem set.mem_inv {α : Type u_1} {s : set α} {a : α} [has_inv α] :

a ∈ s⁻¹ ↔ a⁻¹ ∈ s

@[simp]

theorem set.mem_neg {α : Type u_1} {s : set α} {a : α} [has_neg α] :

a ∈ -s ↔ -a ∈ s

theorem set.inv_mem_inv {α : Type u_1} {s : set α} {a : α} [group α] :

a⁻¹ ∈ s⁻¹ ↔ a ∈ s

theorem set.neg_mem_neg {α : Type u_1} {s : set α} {a : α} [add_group α] :

-a ∈ -s ↔ a ∈ s

@[simp]

theorem set.inv_preimage {α : Type u_1} {s : set α} [has_inv α] :

has_inv.inv ⁻¹' s = s⁻¹

@[simp]

theorem set.neg_preimage {α : Type u_1} {s : set α} [has_neg α] :

has_neg.neg ⁻¹' s = -s

@[simp]

theorem set.image_inv {α : Type u_1} {s : set α} [group α] :

has_inv.inv '' s = s⁻¹

@[simp]

theorem set.image_neg {α : Type u_1} {s : set α} [add_group α] :

has_neg.neg '' s = -s

@[simp]

theorem set.inter_neg {α : Type u_1} {s t : set α} [has_neg α] :

-(s ∩ t) = -s ∩ -t

@[simp]

theorem set.inter_inv {α : Type u_1} {s t : set α} [has_inv α] :

(s ∩ t)⁻¹ = s⁻¹ ∩ t⁻¹

@[simp]

theorem set.union_neg {α : Type u_1} {s t : set α} [has_neg α] :

-(s ∪ t) = -s ∪ -t

@[simp]

theorem set.union_inv {α : Type u_1} {s t : set α} [has_inv α] :

(s ∪ t)⁻¹ = s⁻¹ ∪ t⁻¹

@[simp]

theorem set.compl_neg {α : Type u_1} {s : set α} [has_neg α] :

-sᶜ = (-s)ᶜ

@[simp]

theorem set.compl_inv {α : Type u_1} {s : set α} [has_inv α] :

sᶜ ⁻¹ = s⁻¹ ᶜ

@[simp]

theorem set.neg_neg {α : Type u_1} {s : set α} [add_group α] :

--s = s

@[simp]

theorem set.inv_inv {α : Type u_1} {s : set α} [group α] :

s⁻¹ ⁻¹ = s

@[simp]

theorem set.univ_neg {α : Type u_1} [add_group α] :

-set.univ = set.univ

@[simp]

theorem set.univ_inv {α : Type u_1} [group α] :

set.univ ⁻¹ = set.univ

@[simp]

theorem set.neg_subset_neg {α : Type u_1} [add_group α] {s t : set α} :

-s ⊆ -t ↔ s ⊆ t

@[simp]

theorem set.inv_subset_inv {α : Type u_1} [group α] {s t : set α} :

s⁻¹ ⊆ t⁻¹ ↔ s ⊆ t

theorem set.inv_subset {α : Type u_1} [group α] {s t : set α} :

s⁻¹ ⊆ t ↔ s ⊆ t⁻¹

theorem set.neg_subset {α : Type u_1} [add_group α] {s t : set α} :

-s ⊆ t ↔ s ⊆ -t

Properties about scalar multiplication

@[instance]

def set.has_scalar_set {α : Type u_1} {β : Type u_2} [has_scalar α β] :

has_scalar α (set β)

Scaling a set: multiplying every element by a scalar.

Equations

set.has_scalar_set = {smul := λ (a : α), set.image (has_scalar.smul a)}

@[simp]

theorem set.image_smul {α : Type u_1} {β : Type u_2} {a : α} [has_scalar α β] {t : set β} :

(λ (x : β), a • x) '' t = a • t

theorem set.mem_smul_set {α : Type u_1} {β : Type u_2} {a : α} {x : β} [has_scalar α β] {t : set β} :

x ∈ a • t ↔ ∃ (y : β), y ∈ t ∧ a • y = x

theorem set.smul_mem_smul_set {α : Type u_1} {β : Type u_2} {a : α} {y : β} [has_scalar α β] {t : set β} (hy : y ∈ t) :

a • y ∈ a • t

theorem set.smul_set_union {α : Type u_1} {β : Type u_2} {a : α} [has_scalar α β] {s t : set β} :

a • (s ∪ t) = a • s ∪ a • t

@[simp]

theorem set.smul_set_empty {α : Type u_1} {β : Type u_2} [has_scalar α β] (a : α) :

a • ∅ = ∅

theorem set.smul_set_mono {α : Type u_1} {β : Type u_2} {a : α} [has_scalar α β] {s t : set β} (h : s ⊆ t) :

a • s ⊆ a • t

@[instance]

def set.has_scalar {α : Type u_1} {β : Type u_2} [has_scalar α β] :

has_scalar (set α) (set β)

Pointwise scalar multiplication by a set of scalars.

Equations

set.has_scalar = {smul := set.image2 has_scalar.smul}

@[simp]

theorem set.image2_smul {α : Type u_1} {β : Type u_2} {s : set α} [has_scalar α β] {t : set β} :

set.image2 has_scalar.smul s t = s • t

theorem set.mem_smul {α : Type u_1} {β : Type u_2} {s : set α} {x : β} [has_scalar α β] {t : set β} :

x ∈ s • t ↔ ∃ (a : α) (y : β), a ∈ s ∧ y ∈ t ∧ a • y = x

theorem set.image_smul_prod {α : Type u_1} {β : Type u_2} {s : set α} [has_scalar α β] {t : set β} :

(λ (x : α × β), x.fst • x.snd) '' s.prod t = s • t

theorem set.range_smul_range {α : Type u_1} {β : Type u_2} [has_scalar α β] {ι : Type u_3} {κ : Type u_4} (b : ι → α) (c : κ → β) :

set.range b • set.range c = set.range (λ (p : ι × κ), b p.fst • c p.snd)

theorem set.singleton_smul {α : Type u_1} {β : Type u_2} {a : α} [has_scalar α β] {t : set β} :

{a} • t = a • t

set α as a (∪,*)-semiring

@[instance]

def set.set_semiring.inhabited (α : Type u_1) :

inhabited (set.set_semiring α)

def set.set_semiring (α : Type u_1) :

Type u_1

An alias for set α, which has a semiring structure given by ∪ as "addition" and pointwise multiplication * as "multiplication".

Equations

set.set_semiring α = set α

def set.up {α : Type u_1} (s : set α) :

set.set_semiring α

The identitiy function set α → set_semiring α.

Equations

s.up = s

def set.set_semiring.down {α : Type u_1} (s : set.set_semiring α) :

set α

The identitiy function set_semiring α → set α.

Equations

s.down = s

@[simp]

theorem set.down_up {α : Type u_1} {s : set α} :

@[simp]

theorem set.up_down {α : Type u_1} {s : set.set_semiring α} :

@[instance]

def set.set_semiring.semiring {α : Type u_1} [monoid α] :

semiring (set.set_semiring α)

Equations

set.set_semiring.semiring = {add := λ (s t : set.set_semiring α), s ∪ t, add_assoc := _, zero := ∅, zero_add := _, add_zero := _, add_comm := _, mul := monoid.mul set.monoid, mul_assoc := _, one := monoid.one set.monoid, one_mul := _, mul_one := _, zero_mul := _, mul_zero := _, left_distrib := _, right_distrib := _}

@[instance]

def set.set_semiring.comm_semiring {α : Type u_1} [comm_monoid α] :

comm_semiring (set.set_semiring α)

Equations

set.set_semiring.comm_semiring = {add := semiring.add set.set_semiring.semiring, add_assoc := _, zero := semiring.zero set.set_semiring.semiring, zero_add := _, add_zero := _, add_comm := _, mul := comm_monoid.mul set.comm_monoid, mul_assoc := _, one := comm_monoid.one set.comm_monoid, one_mul := _, mul_one := _, zero_mul := _, mul_zero := _, left_distrib := _, right_distrib := _, mul_comm := _}

@[instance]

def set.mul_action_set {α : Type u_1} {β : Type u_2} [monoid α] [mul_action α β] :

mul_action α (set β)

A multiplicative action of a monoid on a type β gives also a multiplicative action on the subsets of β.

Equations

set.mul_action_set = {to_has_scalar := {smul := has_scalar.smul set.has_scalar_set}, one_smul := _, mul_smul := _}

theorem set.image_add {α : Type u_1} {β : Type u_2} {s t : set α} [has_add α] [has_add β] (m : α → β) [is_add_hom m] :

m '' (s + t) = m '' s + m '' t

theorem set.image_mul {α : Type u_1} {β : Type u_2} {s t : set α} [has_mul α] [has_mul β] (m : α → β) [is_mul_hom m] :

m '' s * t = (m '' s) * m '' t

theorem set.preimage_mul_preimage_subset {α : Type u_1} {β : Type u_2} [has_mul α] [has_mul β] (m : α → β) [is_mul_hom m] {s t : set β} :

(m ⁻¹' s) * m ⁻¹' t ⊆ m ⁻¹' s * t

theorem set.preimage_add_preimage_subset {α : Type u_1} {β : Type u_2} [has_add α] [has_add β] (m : α → β) [is_add_hom m] {s t : set β} :

m ⁻¹' s + m ⁻¹' t ⊆ m ⁻¹' (s + t)

def set.image_hom {α : Type u_1} {β : Type u_2} [monoid α] [monoid β] (f : α →* β) :

set.set_semiring α →+* set.set_semiring β

The image of a set under function is a ring homomorphism with respect to the pointwise operations on sets.

Equations

set.image_hom f = {to_fun := set.image ⇑f, map_one' := _, map_mul' := _, map_zero' := _, map_add' := _}

theorem zero_smul_set {α : Type u_1} {β : Type u_2} [semiring α] [add_comm_monoid β] [semimodule α β] {s : set β} (h : s.nonempty) :

0 • s = 0

A nonempty set in a semimodule is scaled by zero to the singleton containing 0 in the semimodule.

theorem mem_inv_smul_set_iff {α : Type u_1} {β : Type u_2} [field α] [mul_action α β] {a : α} (ha : a ≠ 0) (A : set β) (x : β) :

x ∈ a⁻¹ • A ↔ a • x ∈ A

theorem mem_smul_set_iff_inv_smul_mem {α : Type u_1} {β : Type u_2} [field α] [mul_action α β] {a : α} (ha : a ≠ 0) (A : set β) (x : β) :

x ∈ a • A ↔ a⁻¹ • x ∈ A

@[instance]

def finset.has_add {α : Type u_1} [decidable_eq α] [has_add α] :

has_add (finset α)

The pointwise sum of two finite sets s and t: s + t = { x + y | x ∈ s, y ∈ t }.

@[instance]

def finset.has_mul {α : Type u_1} [decidable_eq α] [has_mul α] :

has_mul (finset α)

The pointwise product of two finite sets s and t: st = s ⬝ t = s * t = { x * y | x ∈ s, y ∈ t }.

Equations

finset.has_mul = {mul := λ (s t : finset α), finset.image (λ (p : α × α), (p.fst) * p.snd) (s.product t)}

theorem finset.add_def {α : Type u_1} [decidable_eq α] [has_add α] {s t : finset α} :

s + t = finset.image (λ (p : α × α), p.fst + p.snd) (s.product t)

theorem finset.mul_def {α : Type u_1} [decidable_eq α] [has_mul α] {s t : finset α} :

s * t = finset.image (λ (p : α × α), (p.fst) * p.snd) (s.product t)

theorem finset.mem_mul {α : Type u_1} [decidable_eq α] [has_mul α] {s t : finset α} {x : α} :

x ∈ s * t ↔ ∃ (y z : α), y ∈ s ∧ z ∈ t ∧ y * z = x

theorem finset.mem_add {α : Type u_1} [decidable_eq α] [has_add α] {s t : finset α} {x : α} :

x ∈ s + t ↔ ∃ (y z : α), y ∈ s ∧ z ∈ t ∧ y + z = x

@[simp]

theorem finset.coe_add {α : Type u_1} [decidable_eq α] [has_add α] {s t : finset α} :

↑(s + t) = ↑s + ↑t

@[simp]

theorem finset.coe_mul {α : Type u_1} [decidable_eq α] [has_mul α] {s t : finset α} :

↑s * t = (↑s) * ↑t

theorem finset.mul_mem_mul {α : Type u_1} [decidable_eq α] [has_mul α] {s t : finset α} {x y : α} (hx : x ∈ s) (hy : y ∈ t) :

x * y ∈ s * t

theorem finset.add_mem_add {α : Type u_1} [decidable_eq α] [has_add α] {s t : finset α} {x y : α} (hx : x ∈ s) (hy : y ∈ t) :

x + y ∈ s + t

theorem finset.add_card_le {α : Type u_1} [decidable_eq α] [has_add α] {s t : finset α} :

(s + t).card ≤ (s.card) * t.card

theorem finset.mul_card_le {α : Type u_1} [decidable_eq α] [has_mul α] {s t : finset α} :

(s * t).card ≤ (s.card) * t.card