α : Type u
β : Type v
γ : Type w
s₂ s₁ s : Finset α
a✝ : α
g f✝ : α → β
inst✝¹ : CommMonoid β
M : Type u_1
inst✝ : AddCommMonoid M
a b : ℕ
f : ℕ → ℕ → M
⊢ ∑ x in Finset.sigma (Ico a b) fun i => Ico i b, f x.fst x.snd =
    ∑ x in Finset.sigma (Ico a b) fun j => Ico a (j + 1), f x.snd x.fst
α : Type u
β : Type v
γ : Type w
s₂ s₁ s : Finset α
a✝ : α
g f✝ : α → β
inst✝¹ : CommMonoid β
M : Type u_1
inst✝ : AddCommMonoid M
a b : ℕ
f : ℕ → ℕ → M
⊢ ∑ i in Ico a b, ∑ j in Ico i b, f i j = ∑ j in Ico a b, ∑ i in Ico a (j + 1), f i j
rw [Finset.sum_sigma', Finset.sum_sigma']
no goals
α : Type u
β : Type v
γ : Type w
s₂ s₁ s : Finset α
a✝ : α
g f✝ : α → β
inst✝¹ : CommMonoid β
M : Type u_1
inst✝ : AddCommMonoid M
a b : ℕ
f : ℕ → ℕ → M
⊢ ∑ x in Finset.sigma (Ico a b) fun i => Ico i b, f x.fst x.snd =
    ∑ x in Finset.sigma (Ico a b) fun j => Ico a (j + 1), f x.snd x.fst
refine'
  Finset.sum_bij' (fun (x : Σ _ : ℕ, ℕ) _ => (⟨x.2, x.1⟩ : Σ _ : ℕ, ℕ)) _ (fun _ _ => rfl)
    (fun (x : Σ _ : ℕ, ℕ) _ => (⟨x.2, x.1⟩ : Σ _ : ℕ, ℕ)) _ (by (rintro ⟨⟩ _; rfl))
    (by (rintro ⟨⟩ _; rfl)) <;>
simp only [Finset.mem_Ico, Sigma.forall, Finset.mem_sigma] <;>
rintro a b ⟨⟨h₁, h₂⟩, ⟨h₃, h₄⟩⟩ <;>
refine' ⟨⟨_, _⟩, ⟨_, _⟩⟩ <;>
linarith
no goals
α : Type u
β : Type v
γ : Type w
s₂ s₁ s : Finset α
a✝ : α
g f✝ : α → β
inst✝¹ : CommMonoid β
M : Type u_1
inst✝ : AddCommMonoid M
a b : ℕ
f : ℕ → ℕ → M
⊢ ∀ (a_1 : (_ : ℕ) × ℕ) (ha : a_1 ∈ Finset.sigma (Ico a b) fun i => Ico i b),
    (fun x x_1 => { fst := x.snd, snd := x.fst }) ((fun x x_1 => { fst := x.snd, snd := x.fst }) a_1 ha)
        (_ : (fun x x_1 => { fst := x.snd, snd := x.fst }) a_1 ha ∈ ?m.29162) =
      a_1
(rintro ⟨⟩ _; rfl)
case mk
α : Type u
β : Type v
γ : Type w
s₂ s₁ s : Finset α
a✝ : α
g f✝ : α → β
inst✝¹ : CommMonoid β
M : Type u_1
inst✝ : AddCommMonoid M
a b : ℕ
f : ℕ → ℕ → M
fst✝ snd✝ : ℕ
ha✝ : { fst := fst✝, snd := snd✝ } ∈ Finset.sigma (Ico a b) fun i => Ico i b
⊢ (fun x x_1 => { fst := x.snd, snd := x.fst })
      ((fun x x_1 => { fst := x.snd, snd := x.fst }) { fst := fst✝, snd := snd✝ } ha✝)
      (_ : (fun x x_1 => { fst := x.snd, snd := x.fst }) { fst := fst✝, snd := snd✝ } ha✝ ∈ ?m.29162) =
    { fst := fst✝, snd := snd✝ }
α : Type u
β : Type v
γ : Type w
s₂ s₁ s : Finset α
a✝ : α
g f✝ : α → β
inst✝¹ : CommMonoid β
M : Type u_1
inst✝ : AddCommMonoid M
a b : ℕ
f : ℕ → ℕ → M
⊢ ∀ (a_1 : (_ : ℕ) × ℕ) (ha : a_1 ∈ Finset.sigma (Ico a b) fun i => Ico i b),
    (fun x x_1 => { fst := x.snd, snd := x.fst }) ((fun x x_1 => { fst := x.snd, snd := x.fst }) a_1 ha)
        (_ : (fun x x_1 => { fst := x.snd, snd := x.fst }) a_1 ha ∈ ?m.29162) =
      a_1
rintro ⟨⟩ _
no goals
case mk
α : Type u
β : Type v
γ : Type w
s₂ s₁ s : Finset α
a✝ : α
g f✝ : α → β
inst✝¹ : CommMonoid β
M : Type u_1
inst✝ : AddCommMonoid M
a b : ℕ
f : ℕ → ℕ → M
fst✝ snd✝ : ℕ
ha✝ : { fst := fst✝, snd := snd✝ } ∈ Finset.sigma (Ico a b) fun i => Ico i b
⊢ (fun x x_1 => { fst := x.snd, snd := x.fst })
      ((fun x x_1 => { fst := x.snd, snd := x.fst }) { fst := fst✝, snd := snd✝ } ha✝)
      (_ : (fun x x_1 => { fst := x.snd, snd := x.fst }) { fst := fst✝, snd := snd✝ } ha✝ ∈ ?m.29162) =
    { fst := fst✝, snd := snd✝ }
rfl
no goals
α : Type u
β : Type v
γ : Type w
s₂ s₁ s : Finset α
a✝ : α
g f✝ : α → β
inst✝¹ : CommMonoid β
M : Type u_1
inst✝ : AddCommMonoid M
a b : ℕ
f : ℕ → ℕ → M
⊢ ∀ (a_1 : (_ : ℕ) × ℕ) (ha : a_1 ∈ Finset.sigma (Ico a b) fun j => Ico a (j + 1)),
    (fun x x_1 => { fst := x.snd, snd := x.fst }) ((fun x x_1 => { fst := x.snd, snd := x.fst }) a_1 ha)
        (_ : (fun x x_1 => { fst := x.snd, snd := x.fst }) a_1 ha ∈ ?m.29161) =
      a_1
(rintro ⟨⟩ _; rfl)
case mk
α : Type u
β : Type v
γ : Type w
s₂ s₁ s : Finset α
a✝ : α
g f✝ : α → β
inst✝¹ : CommMonoid β
M : Type u_1
inst✝ : AddCommMonoid M
a b : ℕ
f : ℕ → ℕ → M
fst✝ snd✝ : ℕ
ha✝ : { fst := fst✝, snd := snd✝ } ∈ Finset.sigma (Ico a b) fun j => Ico a (j + 1)
⊢ (fun x x_1 => { fst := x.snd, snd := x.fst })
      ((fun x x_1 => { fst := x.snd, snd := x.fst }) { fst := fst✝, snd := snd✝ } ha✝)
      (_ : (fun x x_1 => { fst := x.snd, snd := x.fst }) { fst := fst✝, snd := snd✝ } ha✝ ∈ ?m.29161) =
    { fst := fst✝, snd := snd✝ }
α : Type u
β : Type v
γ : Type w
s₂ s₁ s : Finset α
a✝ : α
g f✝ : α → β
inst✝¹ : CommMonoid β
M : Type u_1
inst✝ : AddCommMonoid M
a b : ℕ
f : ℕ → ℕ → M
⊢ ∀ (a_1 : (_ : ℕ) × ℕ) (ha : a_1 ∈ Finset.sigma (Ico a b) fun j => Ico a (j + 1)),
    (fun x x_1 => { fst := x.snd, snd := x.fst }) ((fun x x_1 => { fst := x.snd, snd := x.fst }) a_1 ha)
        (_ : (fun x x_1 => { fst := x.snd, snd := x.fst }) a_1 ha ∈ ?m.29161) =
      a_1
rintro ⟨⟩ _
no goals
case mk
α : Type u
β : Type v
γ : Type w
s₂ s₁ s : Finset α
a✝ : α
g f✝ : α → β
inst✝¹ : CommMonoid β
M : Type u_1
inst✝ : AddCommMonoid M
a b : ℕ
f : ℕ → ℕ → M
fst✝ snd✝ : ℕ
ha✝ : { fst := fst✝, snd := snd✝ } ∈ Finset.sigma (Ico a b) fun j => Ico a (j + 1)
⊢ (fun x x_1 => { fst := x.snd, snd := x.fst })
      ((fun x x_1 => { fst := x.snd, snd := x.fst }) { fst := fst✝, snd := snd✝ } ha✝)
      (_ : (fun x x_1 => { fst := x.snd, snd := x.fst }) { fst := fst✝, snd := snd✝ } ha✝ ∈ ?m.29161) =
    { fst := fst✝, snd := snd✝ }
rfl