-- Mathlib/Topology/Algebra/Module/FiniteDimension.lean
theorem unique_topology_of_t2 {t : TopologicalSpace 𝕜} (h₁ : @IsTopologicalAddGroup 𝕜 t _)
    (h₂ : @ContinuousSMul 𝕜 𝕜 _ hnorm.toUniformSpace.toTopologicalSpace t) (h₃ : @T2Space 𝕜 t) :
    t = hnorm.toUniformSpace.toTopologicalSpace

Proof state:
case neg
𝕜 : Type u
hnorm : NontriviallyNormedField 𝕜
t : TopologicalSpace 𝕜
h₁ : IsTopologicalAddGroup 𝕜
h₂ : ContinuousSMul 𝕜 𝕜
h₃ : T2Space 𝕜
ε : ℝ
hε : 0 < ε
ξ₀ : 𝕜
hξ₀ : 0 < ‖ξ₀‖
hξ₀ε : ‖ξ₀‖ < ε
this✝ : {ξ₀}ᶜ ∈ 𝓝 0
this : balancedCore 𝕜 {ξ₀}ᶜ ∈ 𝓝 0
ξ : 𝕜
hξ : ξ ∈ balancedCore 𝕜 {ξ₀}ᶜ
hξ0 : ¬ξ = 0
h : ε < ‖ξ‖
⊢ ‖ξ₀‖ ≤ ‖ξ‖

Tactic:
exact (hξ₀ε.trans h).le

Result:
no goals

Proof state:
𝕜 : Type u
hnorm : NontriviallyNormedField 𝕜
t : TopologicalSpace 𝕜
h₁ : IsTopologicalAddGroup 𝕜
h₂ : ContinuousSMul 𝕜 𝕜
h₃ : T2Space 𝕜
⊢ 𝓝 (0 • 1) = 𝓝 0

Tactic:
rw [zero_smul]

Result:
no goals

Proof state:
case neg
𝕜 : Type u
hnorm : NontriviallyNormedField 𝕜
t : TopologicalSpace 𝕜
h₁ : IsTopologicalAddGroup 𝕜
h₂ : ContinuousSMul 𝕜 𝕜
h₃ : T2Space 𝕜
ε : ℝ
hε : 0 < ε
ξ₀ : 𝕜
hξ₀ : 0 < ‖ξ₀‖
hξ₀ε : ‖ξ₀‖ < ε
this✝ : {ξ₀}ᶜ ∈ 𝓝 0
this : balancedCore 𝕜 {ξ₀}ᶜ ∈ 𝓝 0
ξ : 𝕜
hξ : ξ ∈ balancedCore 𝕜 {ξ₀}ᶜ
hξ0 : ¬ξ = 0
⊢ ‖ξ‖ ≤ ε

Tactic:
by_contra! h

Result:
case neg
𝕜 : Type u
hnorm : NontriviallyNormedField 𝕜
t : TopologicalSpace 𝕜
h₁ : IsTopologicalAddGroup 𝕜
h₂ : ContinuousSMul 𝕜 𝕜
h₃ : T2Space 𝕜
ε : ℝ
hε : 0 < ε
ξ₀ : 𝕜
hξ₀ : 0 < ‖ξ₀‖
hξ₀ε : ‖ξ₀‖ < ε
this✝ : {ξ₀}ᶜ ∈ 𝓝 0
this : balancedCore 𝕜 {ξ₀}ᶜ ∈ 𝓝 0
ξ : 𝕜
hξ : ξ ∈ balancedCore 𝕜 {ξ₀}ᶜ
hξ0 : ¬ξ = 0
h : ε < ‖ξ‖
⊢ False

Proof state:
case refine_1.intro.intro
𝕜 : Type u
hnorm : NontriviallyNormedField 𝕜
t : TopologicalSpace 𝕜
h₁ : IsTopologicalAddGroup 𝕜
h₂ : ContinuousSMul 𝕜 𝕜
h₃ : T2Space 𝕜
ε : ℝ
hε : 0 < ε
ξ₀ : 𝕜
hξ₀ : 0 < ‖ξ₀‖
hξ₀ε : ‖ξ₀‖ < ε
this✝ : {ξ₀}ᶜ ∈ 𝓝 0
this : balancedCore 𝕜 {ξ₀}ᶜ ∈ 𝓝 0
⊢ Metric.closedBall 0 ε ∈ 𝓝 0

Tactic:
refine mem_of_superset this fun ξ hξ => ?_

Result:
case refine_1.intro.intro
𝕜 : Type u
hnorm : NontriviallyNormedField 𝕜
t : TopologicalSpace 𝕜
h₁ : IsTopologicalAddGroup 𝕜
h₂ : ContinuousSMul 𝕜 𝕜
h₃ : T2Space 𝕜
ε : ℝ
hε : 0 < ε
ξ₀ : 𝕜
hξ₀ : 0 < ‖ξ₀‖
hξ₀ε : ‖ξ₀‖ < ε
this✝ : {ξ₀}ᶜ ∈ 𝓝 0
this : balancedCore 𝕜 {ξ₀}ᶜ ∈ 𝓝 0
ξ : 𝕜
hξ : ξ ∈ balancedCore 𝕜 {ξ₀}ᶜ
⊢ ξ ∈ Metric.closedBall 0 ε

Proof state:
𝕜 : Type u
hnorm : NontriviallyNormedField 𝕜
t : TopologicalSpace 𝕜
h₁ : IsTopologicalAddGroup 𝕜
h₂ : ContinuousSMul 𝕜 𝕜
h₃ : T2Space 𝕜
ε : ℝ
hε : 0 < ε
ξ₀ : 𝕜
hξ₀ : 0 < ‖ξ₀‖
hξ₀ε : ‖ξ₀‖ < ε
this✝¹ : {ξ₀}ᶜ ∈ 𝓝 0
this✝ : balancedCore 𝕜 {ξ₀}ᶜ ∈ 𝓝 0
ξ : 𝕜
hξ : ξ ∈ balancedCore 𝕜 {ξ₀}ᶜ
hξ0 : ¬ξ = 0
h : ε < ‖ξ‖
this : (ξ₀ * ξ⁻¹) • ξ ∈ balancedCore 𝕜 {ξ₀}ᶜ
⊢ False

Tactic:
rw [smul_eq_mul, mul_assoc, inv_mul_cancel₀ hξ0, mul_one] at this

Result:
𝕜 : Type u
hnorm : NontriviallyNormedField 𝕜
t : TopologicalSpace 𝕜
h₁ : IsTopologicalAddGroup 𝕜
h₂ : ContinuousSMul 𝕜 𝕜
h₃ : T2Space 𝕜
ε : ℝ
hε : 0 < ε
ξ₀ : 𝕜
hξ₀ : 0 < ‖ξ₀‖
hξ₀ε : ‖ξ₀‖ < ε
this✝¹ : {ξ₀}ᶜ ∈ 𝓝 0
this✝ : balancedCore 𝕜 {ξ₀}ᶜ ∈ 𝓝 0
ξ : 𝕜
hξ : ξ ∈ balancedCore 𝕜 {ξ₀}ᶜ
hξ0 : ¬ξ = 0
h : ε < ‖ξ‖
this : ξ₀ ∈ balancedCore 𝕜 {ξ₀}ᶜ
⊢ False

Proof state:
case refine_1
𝕜 : Type u
hnorm : NontriviallyNormedField 𝕜
t : TopologicalSpace 𝕜
h₁ : IsTopologicalAddGroup 𝕜
h₂ : ContinuousSMul 𝕜 𝕜
h₃ : T2Space 𝕜
⊢ 𝓝 0 ≤ 𝓝 0

Tactic:
rw [Metric.nhds_basis_closedBall.ge_iff]

Result:
case refine_1
𝕜 : Type u
hnorm : NontriviallyNormedField 𝕜
t : TopologicalSpace 𝕜
h₁ : IsTopologicalAddGroup 𝕜
h₂ : ContinuousSMul 𝕜 𝕜
h₃ : T2Space 𝕜
⊢ ∀ (i' : ℝ), 0 < i' → Metric.closedBall 0 i' ∈ 𝓝 0

Proof state:
case refine_2
𝕜 : Type u
hnorm : NontriviallyNormedField 𝕜
t : TopologicalSpace 𝕜
h₁ : IsTopologicalAddGroup 𝕜
h₂ : ContinuousSMul 𝕜 𝕜
h₃ : T2Space 𝕜
⊢ 𝓝 0 ≤ 𝓝 0

Tactic:
calc
  @nhds 𝕜 hnorm.toUniformSpace.toTopologicalSpace 0 =
      map id (@nhds 𝕜 hnorm.toUniformSpace.toTopologicalSpace 0) :=
    map_id.symm
  _ = map (fun x => id x • (1 : 𝕜)) (@nhds 𝕜 hnorm.toUniformSpace.toTopologicalSpace 0) := by
    conv_rhs =>
      congr
      ext
      rw [smul_eq_mul, mul_one]
  _ ≤ @nhds 𝕜 t ((0 : 𝕜) • (1 : 𝕜)) :=
    (@Tendsto.smul_const _ _ _ hnorm.toUniformSpace.toTopologicalSpace t _ _ _ _ _
      tendsto_id (1 : 𝕜))
  _ = @nhds 𝕜 t 0 := by rw [zero_smul]

Result:
no goals

Proof state:
𝕜 : Type u
hnorm : NontriviallyNormedField 𝕜
t : TopologicalSpace 𝕜
h₁ : IsTopologicalAddGroup 𝕜
h₂ : ContinuousSMul 𝕜 𝕜
h₃ : T2Space 𝕜
⊢ map id (𝓝 0) = map (fun x => id x • 1) (𝓝 0)

Tactic:
conv_rhs =>
  congr
  ext
  rw [smul_eq_mul, mul_one]

Result:
no goals

Proof state:
case refine_1.intro.intro
𝕜 : Type u
hnorm : NontriviallyNormedField 𝕜
t : TopologicalSpace 𝕜
h₁ : IsTopologicalAddGroup 𝕜
h₂ : ContinuousSMul 𝕜 𝕜
h₃ : T2Space 𝕜
ε : ℝ
hε : 0 < ε
ξ₀ : 𝕜
hξ₀ : 0 < ‖ξ₀‖
hξ₀ε : ‖ξ₀‖ < ε
this : {ξ₀}ᶜ ∈ 𝓝 0
⊢ Metric.closedBall 0 ε ∈ 𝓝 0

Tactic:
have : balancedCore 𝕜 {ξ₀}ᶜ ∈ @nhds 𝕜 t 0 := balancedCore_mem_nhds_zero this

Result:
case refine_1.intro.intro
𝕜 : Type u
hnorm : NontriviallyNormedField 𝕜
t : TopologicalSpace 𝕜
h₁ : IsTopologicalAddGroup 𝕜
h₂ : ContinuousSMul 𝕜 𝕜
h₃ : T2Space 𝕜
ε : ℝ
hε : 0 < ε
ξ₀ : 𝕜
hξ₀ : 0 < ‖ξ₀‖
hξ₀ε : ‖ξ₀‖ < ε
this✝ : {ξ₀}ᶜ ∈ 𝓝 0
this : balancedCore 𝕜 {ξ₀}ᶜ ∈ 𝓝 0
⊢ Metric.closedBall 0 ε ∈ 𝓝 0

Proof state:
case refine_1.intro.intro
𝕜 : Type u
hnorm : NontriviallyNormedField 𝕜
t : TopologicalSpace 𝕜
h₁ : IsTopologicalAddGroup 𝕜
h₂ : ContinuousSMul 𝕜 𝕜
h₃ : T2Space 𝕜
ε : ℝ
hε : 0 < ε
ξ₀ : 𝕜
hξ₀ : 0 < ‖ξ₀‖
hξ₀ε : ‖ξ₀‖ < ε
⊢ Metric.closedBall 0 ε ∈ 𝓝 0

Tactic:
have : {ξ₀}ᶜ ∈ @nhds 𝕜 t 0 := IsOpen.mem_nhds isOpen_compl_singleton <|
  mem_compl_singleton_iff.mpr <| Ne.symm <| norm_ne_zero_iff.mp hξ₀.ne.symm

Result:
case refine_1.intro.intro
𝕜 : Type u
hnorm : NontriviallyNormedField 𝕜
t : TopologicalSpace 𝕜
h₁ : IsTopologicalAddGroup 𝕜
h₂ : ContinuousSMul 𝕜 𝕜
h₃ : T2Space 𝕜
ε : ℝ
hε : 0 < ε
ξ₀ : 𝕜
hξ₀ : 0 < ‖ξ₀‖
hξ₀ε : ‖ξ₀‖ < ε
this : {ξ₀}ᶜ ∈ 𝓝 0
⊢ Metric.closedBall 0 ε ∈ 𝓝 0