-- Mathlib/Combinatorics/Additive/ApproximateSubgroup.lean
@[to_additive]
lemma pow_inter_pow_covBySMul_sq_inter_sq
    (hA : IsApproximateSubgroup K A) (hB : IsApproximateSubgroup L B) (hm : 2 ≤ m) (hn : 2 ≤ n) :
    CovBySMul G (K ^ (m - 1) * L ^ (n - 1)) (A ^ m ∩ B ^ n) (A ^ 2 ∩ B ^ 2)

Proof state:
G : Type u_1
inst✝ : Group G
A B : Set G
K L : ℝ
m n : ℕ
hA : IsApproximateSubgroup K A
hB : IsApproximateSubgroup L B
hm : 2 ≤ m
hn : 2 ≤ n
⊢ CovBySMul G (K ^ (m - 1) * L ^ (n - 1)) (A ^ m ∩ B ^ n) (A ^ 2 ∩ B ^ 2)

Tactic:
obtain ⟨F₁, hF₁, hAF₁⟩ := hA.sq_covBySMul

Result:
case intro.intro
G : Type u_1
inst✝ : Group G
A B : Set G
K L : ℝ
m n : ℕ
hA : IsApproximateSubgroup K A
hB : IsApproximateSubgroup L B
hm : 2 ≤ m
hn : 2 ≤ n
F₁ : Finset G
hF₁ : ↑(#F₁) ≤ K
hAF₁ : A ^ 2 ⊆ ↑F₁ • A
⊢ CovBySMul G (K ^ (m - 1) * L ^ (n - 1)) (A ^ m ∩ B ^ n) (A ^ 2 ∩ B ^ 2)

Proof state:
G : Type u_1
inst✝ : Group G
A B : Set G
K L : ℝ
m n : ℕ
hA : IsApproximateSubgroup K A
hB : IsApproximateSubgroup L B
hm : 2 ≤ m
hn : 2 ≤ n
F₁ : Finset G
hF₁ : ↑(#F₁) ≤ K
hAF₁ : A ^ 2 ⊆ ↑F₁ • A
F₂ : Finset G
hF₂ : ↑(#F₂) ≤ L
hBF₂ : B ^ 2 ⊆ ↑F₂ • B
this : 1 ≤ K
f : G → G → G
hf : ∀ (a b : G), a • A ∩ b • B ⊆ f a b • (A⁻¹ * A ∩ (B⁻¹ * B))
⊢ ⋃ a ∈ F₁ ^ (m - 1), ⋃ b ∈ F₂ ^ (n - 1), f a b • (A⁻¹ * A ∩ (B⁻¹ * B)) =
    ↑(Finset.image₂ f (F₁ ^ (m - 1)) (F₂ ^ (n - 1))) * (A ^ 2 ∩ B ^ 2)

Tactic:
simp_rw [hA.inv_eq_self, hB.inv_eq_self, ← sq]

Result:
G : Type u_1
inst✝ : Group G
A B : Set G
K L : ℝ
m n : ℕ
hA : IsApproximateSubgroup K A
hB : IsApproximateSubgroup L B
hm : 2 ≤ m
hn : 2 ≤ n
F₁ : Finset G
hF₁ : ↑(#F₁) ≤ K
hAF₁ : A ^ 2 ⊆ ↑F₁ • A
F₂ : Finset G
hF₂ : ↑(#F₂) ≤ L
hBF₂ : B ^ 2 ⊆ ↑F₂ • B
this : 1 ≤ K
f : G → G → G
hf : ∀ (a b : G), a • A ∩ b • B ⊆ f a b • (A⁻¹ * A ∩ (B⁻¹ * B))
⊢ ⋃ a ∈ F₁ ^ (m - 1), ⋃ b ∈ F₂ ^ (n - 1), f a b • (A ^ 2 ∩ B ^ 2) =
    ↑(Finset.image₂ f (F₁ ^ (m - 1)) (F₂ ^ (n - 1))) * (A ^ 2 ∩ B ^ 2)

Proof state:
G : Type u_1
inst✝ : Group G
A B : Set G
K L : ℝ
m n : ℕ
hA : IsApproximateSubgroup K A
hB : IsApproximateSubgroup L B
hm : 2 ≤ m
hn : 2 ≤ n
F₁ : Finset G
hF₁ : ↑(#F₁) ≤ K
hAF₁ : A ^ 2 ⊆ ↑F₁ • A
F₂ : Finset G
hF₂ : ↑(#F₂) ≤ L
hBF₂ : B ^ 2 ⊆ ↑F₂ • B
this : 1 ≤ K
f : G → G → G
hf : ∀ (a b : G), a • A ∩ b • B ⊆ f a b • (A⁻¹ * A ∩ (B⁻¹ * B))
⊢ ↑(#F₁) ^ (m - 1) * ↑(#F₂) ^ (n - 1) ≤ K ^ (m - 1) * L ^ (n - 1)

Tactic:
gcongr

Result:
no goals

Proof state:
G : Type u_1
inst✝ : Group G
A B : Set G
K L : ℝ
m n : ℕ
hA : IsApproximateSubgroup K A
hB : IsApproximateSubgroup L B
hm : 2 ≤ m
hn : 2 ≤ n
F₁ : Finset G
hF₁ : ↑(#F₁) ≤ K
hAF₁ : A ^ 2 ⊆ ↑F₁ • A
F₂ : Finset G
hF₂ : ↑(#F₂) ≤ L
hBF₂ : B ^ 2 ⊆ ↑F₂ • B
this : 1 ≤ K
f : G → G → G
hf : ∀ (a b : G), a • A ∩ b • B ⊆ f a b • (A⁻¹ * A ∩ (B⁻¹ * B))
⊢ ⋃ i₁ ∈ ↑F₁ ^ (m - 1), ⋃ j₁ ∈ ↑F₂ ^ (n - 1), i₁ • A ∩ j₁ • B = ⋃ a ∈ F₁ ^ (m - 1), ⋃ b ∈ F₂ ^ (n - 1), a • A ∩ b • B

Tactic:
norm_cast

Result:
no goals

Proof state:
case intro.intro.intro.intro
G : Type u_1
inst✝ : Group G
A B : Set G
K L : ℝ
m n : ℕ
hA : IsApproximateSubgroup K A
hB : IsApproximateSubgroup L B
hm : 2 ≤ m
hn : 2 ≤ n
F₁ : Finset G
hF₁ : ↑(#F₁) ≤ K
hAF₁ : A ^ 2 ⊆ ↑F₁ • A
F₂ : Finset G
hF₂ : ↑(#F₂) ≤ L
hBF₂ : B ^ 2 ⊆ ↑F₂ • B
this : 1 ≤ K
⊢ CovBySMul G (K ^ (m - 1) * L ^ (n - 1)) (A ^ m ∩ B ^ n) (A ^ 2 ∩ B ^ 2)

Tactic:
choose f hf using exists_smul_inter_smul_subset_smul_inv_mul_inter_inv_mul A B

Result:
case intro.intro.intro.intro
G : Type u_1
inst✝ : Group G
A B : Set G
K L : ℝ
m n : ℕ
hA : IsApproximateSubgroup K A
hB : IsApproximateSubgroup L B
hm : 2 ≤ m
hn : 2 ≤ n
F₁ : Finset G
hF₁ : ↑(#F₁) ≤ K
hAF₁ : A ^ 2 ⊆ ↑F₁ • A
F₂ : Finset G
hF₂ : ↑(#F₂) ≤ L
hBF₂ : B ^ 2 ⊆ ↑F₂ • B
this : 1 ≤ K
f : G → G → G
hf : ∀ (a b : G), a • A ∩ b • B ⊆ f a b • (A⁻¹ * A ∩ (B⁻¹ * B))
⊢ CovBySMul G (K ^ (m - 1) * L ^ (n - 1)) (A ^ m ∩ B ^ n) (A ^ 2 ∩ B ^ 2)

Proof state:
G : Type u_1
inst✝ : Group G
A B : Set G
K L : ℝ
m n : ℕ
hA : IsApproximateSubgroup K A
hB : IsApproximateSubgroup L B
hm : 2 ≤ m
hn : 2 ≤ n
F₁ : Finset G
hF₁ : ↑(#F₁) ≤ K
hAF₁ : A ^ 2 ⊆ ↑F₁ • A
F₂ : Finset G
hF₂ : ↑(#F₂) ≤ L
hBF₂ : B ^ 2 ⊆ ↑F₂ • B
this : 1 ≤ K
f : G → G → G
hf : ∀ (a b : G), a • A ∩ b • B ⊆ f a b • (A⁻¹ * A ∩ (B⁻¹ * B))
⊢ ↑F₁ ^ (m - 1) * A ∩ (↑F₂ ^ (n - 1) * B) = ⋃ a ∈ F₁ ^ (m - 1), ⋃ b ∈ F₂ ^ (n - 1), a • A ∩ b • B

Tactic:
simp_rw [← smul_eq_mul, ← iUnion_smul_set, iUnion₂_inter_iUnion₂]

Result:
G : Type u_1
inst✝ : Group G
A B : Set G
K L : ℝ
m n : ℕ
hA : IsApproximateSubgroup K A
hB : IsApproximateSubgroup L B
hm : 2 ≤ m
hn : 2 ≤ n
F₁ : Finset G
hF₁ : ↑(#F₁) ≤ K
hAF₁ : A ^ 2 ⊆ ↑F₁ • A
F₂ : Finset G
hF₂ : ↑(#F₂) ≤ L
hBF₂ : B ^ 2 ⊆ ↑F₂ • B
this : 1 ≤ K
f : G → G → G
hf : ∀ (a b : G), a • A ∩ b • B ⊆ f a b • (A⁻¹ * A ∩ (B⁻¹ * B))
⊢ ⋃ i₁ ∈ ↑F₁ ^ (m - 1), ⋃ j₁ ∈ ↑F₂ ^ (n - 1), i₁ • A ∩ j₁ • B = ⋃ a ∈ F₁ ^ (m - 1), ⋃ b ∈ F₂ ^ (n - 1), a • A ∩ b • B

Proof state:
case intro.intro.intro.intro.refine_1
G : Type u_1
inst✝ : Group G
A B : Set G
K L : ℝ
m n : ℕ
hA : IsApproximateSubgroup K A
hB : IsApproximateSubgroup L B
hm : 2 ≤ m
hn : 2 ≤ n
F₁ : Finset G
hF₁ : ↑(#F₁) ≤ K
hAF₁ : A ^ 2 ⊆ ↑F₁ • A
F₂ : Finset G
hF₂ : ↑(#F₂) ≤ L
hBF₂ : B ^ 2 ⊆ ↑F₂ • B
this : 1 ≤ K
f : G → G → G
hf : ∀ (a b : G), a • A ∩ b • B ⊆ f a b • (A⁻¹ * A ∩ (B⁻¹ * B))
⊢ ↑(#(Finset.image₂ f (F₁ ^ (m - 1)) (F₂ ^ (n - 1)))) ≤ K ^ (m - 1) * L ^ (n - 1)

Tactic:
calc
  (#(.image₂ f (F₁ ^ (m - 1)) (F₂ ^ (n - 1))) : ℝ)
  _ ≤ #(F₁ ^ (m - 1)) * #(F₂ ^ (n - 1)) := mod_cast Finset.card_image₂_le ..
  _ ≤ #F₁ ^ (m - 1) * #F₂ ^ (n - 1) := by gcongr <;> exact mod_cast Finset.card_pow_le
  _ ≤ K ^ (m - 1) * L ^ (n - 1) := by gcongr

Result:
no goals

Proof state:
case intro.intro.intro.intro
G : Type u_1
inst✝ : Group G
A B : Set G
K L : ℝ
m n : ℕ
hA : IsApproximateSubgroup K A
hB : IsApproximateSubgroup L B
hm : 2 ≤ m
hn : 2 ≤ n
F₁ : Finset G
hF₁ : ↑(#F₁) ≤ K
hAF₁ : A ^ 2 ⊆ ↑F₁ • A
F₂ : Finset G
hF₂ : ↑(#F₂) ≤ L
hBF₂ : B ^ 2 ⊆ ↑F₂ • B
this : 1 ≤ K
f : G → G → G
hf : ∀ (a b : G), a • A ∩ b • B ⊆ f a b • (A⁻¹ * A ∩ (B⁻¹ * B))
⊢ CovBySMul G (K ^ (m - 1) * L ^ (n - 1)) (A ^ m ∩ B ^ n) (A ^ 2 ∩ B ^ 2)

Tactic:
refine ⟨.image₂ f (F₁ ^ (m - 1)) (F₂ ^ (n - 1)), ?_, ?_⟩

Result:
case intro.intro.intro.intro.refine_1
G : Type u_1
inst✝ : Group G
A B : Set G
K L : ℝ
m n : ℕ
hA : IsApproximateSubgroup K A
hB : IsApproximateSubgroup L B
hm : 2 ≤ m
hn : 2 ≤ n
F₁ : Finset G
hF₁ : ↑(#F₁) ≤ K
hAF₁ : A ^ 2 ⊆ ↑F₁ • A
F₂ : Finset G
hF₂ : ↑(#F₂) ≤ L
hBF₂ : B ^ 2 ⊆ ↑F₂ • B
this : 1 ≤ K
f : G → G → G
hf : ∀ (a b : G), a • A ∩ b • B ⊆ f a b • (A⁻¹ * A ∩ (B⁻¹ * B))
⊢ ↑(#(Finset.image₂ f (F₁ ^ (m - 1)) (F₂ ^ (n - 1)))) ≤ K ^ (m - 1) * L ^ (n - 1)

case intro.intro.intro.intro.refine_2
G : Type u_1
inst✝ : Group G
A B : Set G
K L : ℝ
m n : ℕ
hA : IsApproximateSubgroup K A
hB : IsApproximateSubgroup L B
hm : 2 ≤ m
hn : 2 ≤ n
F₁ : Finset G
hF₁ : ↑(#F₁) ≤ K
hAF₁ : A ^ 2 ⊆ ↑F₁ • A
F₂ : Finset G
hF₂ : ↑(#F₂) ≤ L
hBF₂ : B ^ 2 ⊆ ↑F₂ • B
this : 1 ≤ K
f : G → G → G
hf : ∀ (a b : G), a • A ∩ b • B ⊆ f a b • (A⁻¹ * A ∩ (B⁻¹ * B))
⊢ A ^ m ∩ B ^ n ⊆ ↑(Finset.image₂ f (F₁ ^ (m - 1)) (F₂ ^ (n - 1))) • (A ^ 2 ∩ B ^ 2)