-- Mathlib/Analysis/NormedSpace/OperatorNorm/Basic.lean
private lemma uniformity_eq_seminorm :
    𝓤 (E →SL[σ₁₂] F) = ⨅ r > 0, 𝓟 {f | ‖f.1 - f.2‖ < r}

Proof state:
case refine_1.intro
𝕜 : Type u_1
𝕜₂ : Type u_2
E : Type u_4
F : Type u_5
inst✝⁶ : SeminormedAddCommGroup E
inst✝⁵ : SeminormedAddCommGroup F
inst✝⁴ : NontriviallyNormedField 𝕜
inst✝³ : NontriviallyNormedField 𝕜₂
inst✝² : NormedSpace 𝕜 E
inst✝¹ : NormedSpace 𝕜₂ F
σ₁₂ : 𝕜 →+* 𝕜₂
inst✝ : RingHomIsometric σ₁₂
c : 𝕜
hc : 1 < ‖c‖
⊢ (IsVonNBounded 𝕜 (closedBall 0 1, closedBall 0 1).1 ∧ (closedBall 0 1, closedBall 0 1).2 ∈ 𝓝 0) ∧
    {f | ∀ x ∈ (closedBall 0 1, closedBall 0 1).1, f x ∈ (closedBall 0 1, closedBall 0 1).2} ⊆
      ContinuousLinearMap.seminorm.closedBall 0 ‖c‖

Tactic:
suffices ∀ f : E →SL[σ₁₂] F, (∀ x, ‖x‖ ≤ 1 → ‖f x‖ ≤ 1) → ‖f‖ ≤ ‖c‖ by
  simpa [NormedSpace.isVonNBounded_closedBall, closedBall_mem_nhds, subset_def] using this

Result:
case refine_1.intro
𝕜 : Type u_1
𝕜₂ : Type u_2
E : Type u_4
F : Type u_5
inst✝⁶ : SeminormedAddCommGroup E
inst✝⁵ : SeminormedAddCommGroup F
inst✝⁴ : NontriviallyNormedField 𝕜
inst✝³ : NontriviallyNormedField 𝕜₂
inst✝² : NormedSpace 𝕜 E
inst✝¹ : NormedSpace 𝕜₂ F
σ₁₂ : 𝕜 →+* 𝕜₂
inst✝ : RingHomIsometric σ₁₂
c : 𝕜
hc : 1 < ‖c‖
⊢ ∀ (f : E →SL[σ₁₂] F), (∀ (x : E), ‖x‖ ≤ 1 → ‖f x‖ ≤ 1) → ‖f‖ ≤ ‖c‖

Proof state:
𝕜 : Type u_1
𝕜₂ : Type u_2
E : Type u_4
F : Type u_5
inst✝⁶ : SeminormedAddCommGroup E
inst✝⁵ : SeminormedAddCommGroup F
inst✝⁴ : NontriviallyNormedField 𝕜
inst✝³ : NontriviallyNormedField 𝕜₂
inst✝² : NormedSpace 𝕜 E
inst✝¹ : NormedSpace 𝕜₂ F
σ₁₂ : 𝕜 →+* 𝕜₂
inst✝ : RingHomIsometric σ₁₂
⊢ 𝓤 (E →SL[σ₁₂] F) = ⨅ r, ⨅ (_ : r > 0), 𝓟 {f | ‖f.1 - f.2‖ < r}

Tactic:
refine ContinuousLinearMap.seminorm (σ₁₂ := σ₁₂) (E := E) (F := F) |>.uniformity_eq_of_hasBasis
  (ContinuousLinearMap.hasBasis_nhds_zero_of_basis Metric.nhds_basis_closedBall)
  ?_ fun (s, r) ⟨hs, hr⟩ ↦ ?_

Result:
case refine_1
𝕜 : Type u_1
𝕜₂ : Type u_2
E : Type u_4
F : Type u_5
inst✝⁶ : SeminormedAddCommGroup E
inst✝⁵ : SeminormedAddCommGroup F
inst✝⁴ : NontriviallyNormedField 𝕜
inst✝³ : NontriviallyNormedField 𝕜₂
inst✝² : NormedSpace 𝕜 E
inst✝¹ : NormedSpace 𝕜₂ F
σ₁₂ : 𝕜 →+* 𝕜₂
inst✝ : RingHomIsometric σ₁₂
⊢ ∃ r, ContinuousLinearMap.seminorm.closedBall 0 r ∈ 𝓝 0

case refine_2
𝕜 : Type u_1
𝕜₂ : Type u_2
E : Type u_4
F : Type u_5
inst✝⁶ : SeminormedAddCommGroup E
inst✝⁵ : SeminormedAddCommGroup F
inst✝⁴ : NontriviallyNormedField 𝕜
inst✝³ : NontriviallyNormedField 𝕜₂
inst✝² : NormedSpace 𝕜 E
inst✝¹ : NormedSpace 𝕜₂ F
σ₁₂ : 𝕜 →+* 𝕜₂
inst✝ : RingHomIsometric σ₁₂
x✝¹ : Set E × ℝ
s : Set E
r : ℝ
x✝ : IsVonNBounded 𝕜 (s, r).1 ∧ 0 < (s, r).2
hs : IsVonNBounded 𝕜 (s, r).1
hr : 0 < (s, r).2
⊢ ∃ r_1 > 0, ContinuousLinearMap.seminorm.ball 0 r_1 ⊆ {f | ∀ x ∈ (s, r).1, f x ∈ closedBall 0 (s, r).2}

Proof state:
case refine_1.intro
𝕜 : Type u_1
𝕜₂ : Type u_2
E : Type u_4
F : Type u_5
inst✝⁶ : SeminormedAddCommGroup E
inst✝⁵ : SeminormedAddCommGroup F
inst✝⁴ : NontriviallyNormedField 𝕜
inst✝³ : NontriviallyNormedField 𝕜₂
inst✝² : NormedSpace 𝕜 E
inst✝¹ : NormedSpace 𝕜₂ F
σ₁₂ : 𝕜 →+* 𝕜₂
inst✝ : RingHomIsometric σ₁₂
c : 𝕜
hc : 1 < ‖c‖
f : E →SL[σ₁₂] F
hf : ∀ (x : E), ‖x‖ ≤ 1 → ‖f x‖ ≤ 1
x : E
hcx : 1 / ‖c‖ ≤ ‖x‖
hx : ‖x‖ < 1
⊢ ‖f x‖ ≤ ‖c‖ * ‖x‖

Tactic:
exact (hf x hx.le).trans ((div_le_iff₀' <| one_pos.trans hc).1 hcx)

Result:
no goals

Proof state:
case refine_1
𝕜 : Type u_1
𝕜₂ : Type u_2
E : Type u_4
F : Type u_5
inst✝⁶ : SeminormedAddCommGroup E
inst✝⁵ : SeminormedAddCommGroup F
inst✝⁴ : NontriviallyNormedField 𝕜
inst✝³ : NontriviallyNormedField 𝕜₂
inst✝² : NormedSpace 𝕜 E
inst✝¹ : NormedSpace 𝕜₂ F
σ₁₂ : 𝕜 →+* 𝕜₂
inst✝ : RingHomIsometric σ₁₂
⊢ ∃ r, ContinuousLinearMap.seminorm.closedBall 0 r ∈ 𝓝 0

Tactic:
rcases NormedField.exists_lt_norm 𝕜 1 with ⟨c, hc⟩

Result:
case refine_1.intro
𝕜 : Type u_1
𝕜₂ : Type u_2
E : Type u_4
F : Type u_5
inst✝⁶ : SeminormedAddCommGroup E
inst✝⁵ : SeminormedAddCommGroup F
inst✝⁴ : NontriviallyNormedField 𝕜
inst✝³ : NontriviallyNormedField 𝕜₂
inst✝² : NormedSpace 𝕜 E
inst✝¹ : NormedSpace 𝕜₂ F
σ₁₂ : 𝕜 →+* 𝕜₂
inst✝ : RingHomIsometric σ₁₂
c : 𝕜
hc : 1 < ‖c‖
⊢ ∃ r, ContinuousLinearMap.seminorm.closedBall 0 r ∈ 𝓝 0

Proof state:
case refine_1.intro
𝕜 : Type u_1
𝕜₂ : Type u_2
E : Type u_4
F : Type u_5
inst✝⁶ : SeminormedAddCommGroup E
inst✝⁵ : SeminormedAddCommGroup F
inst✝⁴ : NontriviallyNormedField 𝕜
inst✝³ : NontriviallyNormedField 𝕜₂
inst✝² : NormedSpace 𝕜 E
inst✝¹ : NormedSpace 𝕜₂ F
σ₁₂ : 𝕜 →+* 𝕜₂
inst✝ : RingHomIsometric σ₁₂
c : 𝕜
hc : 1 < ‖c‖
⊢ ∀ (f : E →SL[σ₁₂] F), (∀ (x : E), ‖x‖ ≤ 1 → ‖f x‖ ≤ 1) → ‖f‖ ≤ ‖c‖

Tactic:
intro f hf

Result:
case refine_1.intro
𝕜 : Type u_1
𝕜₂ : Type u_2
E : Type u_4
F : Type u_5
inst✝⁶ : SeminormedAddCommGroup E
inst✝⁵ : SeminormedAddCommGroup F
inst✝⁴ : NontriviallyNormedField 𝕜
inst✝³ : NontriviallyNormedField 𝕜₂
inst✝² : NormedSpace 𝕜 E
inst✝¹ : NormedSpace 𝕜₂ F
σ₁₂ : 𝕜 →+* 𝕜₂
inst✝ : RingHomIsometric σ₁₂
c : 𝕜
hc : 1 < ‖c‖
f : E →SL[σ₁₂] F
hf : ∀ (x : E), ‖x‖ ≤ 1 → ‖f x‖ ≤ 1
⊢ ‖f‖ ≤ ‖c‖

Proof state:
case refine_2.intro
𝕜 : Type u_1
𝕜₂ : Type u_2
E : Type u_4
F : Type u_5
inst✝⁶ : SeminormedAddCommGroup E
inst✝⁵ : SeminormedAddCommGroup F
inst✝⁴ : NontriviallyNormedField 𝕜
inst✝³ : NontriviallyNormedField 𝕜₂
inst✝² : NormedSpace 𝕜 E
inst✝¹ : NormedSpace 𝕜₂ F
σ₁₂ : 𝕜 →+* 𝕜₂
inst✝ : RingHomIsometric σ₁₂
x✝¹ : Set E × ℝ
s : Set E
r : ℝ
x✝ : IsVonNBounded 𝕜 (s, r).1 ∧ 0 < (s, r).2
hs : IsVonNBounded 𝕜 (s, r).1
hr : 0 < (s, r).2
ε : ℝ
hε : ∀ x ∈ (s, r).1, ‖x‖ ≤ ε
⊢ ∃ r_1 > 0, ContinuousLinearMap.seminorm.ball 0 r_1 ⊆ {f | ∀ x ∈ (s, r).1, f x ∈ closedBall 0 (s, r).2}

Tactic:
rcases exists_pos_mul_lt hr ε with ⟨δ, hδ₀, hδ⟩

Result:
case refine_2.intro.intro.intro
𝕜 : Type u_1
𝕜₂ : Type u_2
E : Type u_4
F : Type u_5
inst✝⁶ : SeminormedAddCommGroup E
inst✝⁵ : SeminormedAddCommGroup F
inst✝⁴ : NontriviallyNormedField 𝕜
inst✝³ : NontriviallyNormedField 𝕜₂
inst✝² : NormedSpace 𝕜 E
inst✝¹ : NormedSpace 𝕜₂ F
σ₁₂ : 𝕜 →+* 𝕜₂
inst✝ : RingHomIsometric σ₁₂
x✝¹ : Set E × ℝ
s : Set E
r : ℝ
x✝ : IsVonNBounded 𝕜 (s, r).1 ∧ 0 < (s, r).2
hs : IsVonNBounded 𝕜 (s, r).1
hr : 0 < (s, r).2
ε : ℝ
hε : ∀ x ∈ (s, r).1, ‖x‖ ≤ ε
δ : ℝ
hδ₀ : 0 < δ
hδ : ε * δ < (s, r).2
⊢ ∃ r_1 > 0, ContinuousLinearMap.seminorm.ball 0 r_1 ⊆ {f | ∀ x ∈ (s, r).1, f x ∈ closedBall 0 (s, r).2}

Proof state:
𝕜 : Type u_1
𝕜₂ : Type u_2
E : Type u_4
F : Type u_5
inst✝⁶ : SeminormedAddCommGroup E
inst✝⁵ : SeminormedAddCommGroup F
inst✝⁴ : NontriviallyNormedField 𝕜
inst✝³ : NontriviallyNormedField 𝕜₂
inst✝² : NormedSpace 𝕜 E
inst✝¹ : NormedSpace 𝕜₂ F
σ₁₂ : 𝕜 →+* 𝕜₂
inst✝ : RingHomIsometric σ₁₂
c : 𝕜
hc : 1 < ‖c‖
this : ∀ (f : E →SL[σ₁₂] F), (∀ (x : E), ‖x‖ ≤ 1 → ‖f x‖ ≤ 1) → ‖f‖ ≤ ‖c‖
⊢ (IsVonNBounded 𝕜 (closedBall 0 1, closedBall 0 1).1 ∧ (closedBall 0 1, closedBall 0 1).2 ∈ 𝓝 0) ∧
    {f | ∀ x ∈ (closedBall 0 1, closedBall 0 1).1, f x ∈ (closedBall 0 1, closedBall 0 1).2} ⊆
      ContinuousLinearMap.seminorm.closedBall 0 ‖c‖

Tactic:
simpa [NormedSpace.isVonNBounded_closedBall, closedBall_mem_nhds, subset_def] using this

Result:
no goals