-- Mathlib/Analysis/Complex/AbsMax.lean
theorem norm_max_aux₁ [CompleteSpace F] {f : ℂ → F} {z w : ℂ}
    (hd : DiffContOnCl ℂ f (ball z (dist w z)))
    (hz : IsMaxOn (norm ∘ f) (closedBall z (dist w z)) z) : ‖f w‖ = ‖f z‖

Proof state:
case refine_2
F : Type v
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℂ F
inst✝ : CompleteSpace F
f : ℂ → F
z w : ℂ
r : ℝ := dist w z
hd : DiffContOnCl ℂ f (ball z r)
hz : IsMaxOn (norm ∘ f) (closedBall z r) z
hw : w ∈ closedBall z r
hw_lt : ‖f w‖ < ‖f z‖
hr : 0 < r
hsub : sphere z r ⊆ closedBall z r
⊢ ∀ ζ ∈ sphere z r, ‖(ζ - z)⁻¹ • f ζ‖ ≤ ‖f z‖ / r

Tactic:
rintro ζ (hζ : ‖ζ - z‖ = r)

Result:
case refine_2
F : Type v
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℂ F
inst✝ : CompleteSpace F
f : ℂ → F
z w : ℂ
r : ℝ := dist w z
hd : DiffContOnCl ℂ f (ball z r)
hz : IsMaxOn (norm ∘ f) (closedBall z r) z
hw : w ∈ closedBall z r
hw_lt : ‖f w‖ < ‖f z‖
hr : 0 < r
hsub : sphere z r ⊆ closedBall z r
ζ : ℂ
hζ : ‖ζ - z‖ = r
⊢ ‖(ζ - z)⁻¹ • f ζ‖ ≤ ‖f z‖ / r

Proof state:
case refine_1
F : Type v
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℂ F
inst✝ : CompleteSpace F
f : ℂ → F
z w : ℂ
r : ℝ := dist w z
hd : DiffContOnCl ℂ f (ball z r)
hz : IsMaxOn (norm ∘ f) (closedBall z r) z
hw : w ∈ closedBall z r
hw_lt : ‖f w‖ < ‖f z‖
hr : 0 < r
hsub : sphere z r ⊆ closedBall z r
⊢ ∀ x ∈ sphere z r, _root_.id x - z ≠ 0

Tactic:
exact fun ζ hζ => sub_ne_zero.2 (ne_of_mem_sphere hζ hr.ne')

Result:
no goals

Proof state:
F : Type v
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℂ F
inst✝ : CompleteSpace F
f : ℂ → F
z w : ℂ
r : ℝ := dist w z
hd : DiffContOnCl ℂ f (ball z r)
hz : IsMaxOn (norm ∘ f) (closedBall z r) z
hw : w ∈ closedBall z r
hw_lt : ‖f w‖ < ‖f z‖
hr : 0 < r
this : ‖∮ (ζ : ℂ) in C(z, r), (ζ - z)⁻¹ • f ζ‖ < 2 * π * ‖f z‖
⊢ False

Tactic:
refine this.ne ?_

Result:
F : Type v
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℂ F
inst✝ : CompleteSpace F
f : ℂ → F
z w : ℂ
r : ℝ := dist w z
hd : DiffContOnCl ℂ f (ball z r)
hz : IsMaxOn (norm ∘ f) (closedBall z r) z
hw : w ∈ closedBall z r
hw_lt : ‖f w‖ < ‖f z‖
hr : 0 < r
this : ‖∮ (ζ : ℂ) in C(z, r), (ζ - z)⁻¹ • f ζ‖ < 2 * π * ‖f z‖
⊢ ‖∮ (ζ : ℂ) in C(z, r), (ζ - z)⁻¹ • f ζ‖ = 2 * π * ‖f z‖

Proof state:
F : Type v
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℂ F
inst✝ : CompleteSpace F
f : ℂ → F
z w : ℂ
r : ℝ := dist w z
hd : DiffContOnCl ℂ f (ball z r)
hz : IsMaxOn (norm ∘ f) (closedBall z r) z
hw : w ∈ closedBall z r
⊢ ¬(norm ∘ f) w < (norm ∘ f) z

Tactic:
rintro hw_lt : ‖f w‖ < ‖f z‖

Result:
F : Type v
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℂ F
inst✝ : CompleteSpace F
f : ℂ → F
z w : ℂ
r : ℝ := dist w z
hd : DiffContOnCl ℂ f (ball z r)
hz : IsMaxOn (norm ∘ f) (closedBall z r) z
hw : w ∈ closedBall z r
hw_lt : ‖f w‖ < ‖f z‖
⊢ False

Proof state:
case refine_1
F : Type v
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℂ F
inst✝ : CompleteSpace F
f : ℂ → F
z w : ℂ
r : ℝ := dist w z
hd : DiffContOnCl ℂ f (ball z r)
hz : IsMaxOn (norm ∘ f) (closedBall z r) z
hw : w ∈ closedBall z r
hw_lt : ‖f w‖ < ‖f z‖
hr : 0 < r
hsub : sphere z r ⊆ closedBall z r
⊢ ContinuousOn (fun ζ => (ζ - z)⁻¹ • f ζ) (sphere z r)

Tactic:
refine ((continuousOn_id.sub continuousOn_const).inv₀ ?_).smul (hd.continuousOn_ball.mono hsub)

Result:
case refine_1
F : Type v
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℂ F
inst✝ : CompleteSpace F
f : ℂ → F
z w : ℂ
r : ℝ := dist w z
hd : DiffContOnCl ℂ f (ball z r)
hz : IsMaxOn (norm ∘ f) (closedBall z r) z
hw : w ∈ closedBall z r
hw_lt : ‖f w‖ < ‖f z‖
hr : 0 < r
hsub : sphere z r ⊆ closedBall z r
⊢ ∀ x ∈ sphere z r, _root_.id x - z ≠ 0

Proof state:
case refine_3
F : Type v
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℂ F
inst✝ : CompleteSpace F
f : ℂ → F
z w : ℂ
r : ℝ := dist w z
hd : DiffContOnCl ℂ f (ball z r)
hz : IsMaxOn (norm ∘ f) (closedBall z r) z
hw : w ∈ closedBall z r
hw_lt : ‖f w‖ < ‖f z‖
hr : 0 < r
hsub : sphere z r ⊆ closedBall z r
⊢ ‖(w - z)⁻¹ • f w‖ < ‖f z‖ / r

Tactic:
rw [norm_smul, norm_inv, ← div_eq_inv_mul]

Result:
case refine_3
F : Type v
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℂ F
inst✝ : CompleteSpace F
f : ℂ → F
z w : ℂ
r : ℝ := dist w z
hd : DiffContOnCl ℂ f (ball z r)
hz : IsMaxOn (norm ∘ f) (closedBall z r) z
hw : w ∈ closedBall z r
hw_lt : ‖f w‖ < ‖f z‖
hr : 0 < r
hsub : sphere z r ⊆ closedBall z r
⊢ ‖f w‖ / ‖w - z‖ < ‖f z‖ / r

Proof state:
F : Type v
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℂ F
inst✝ : CompleteSpace F
f : ℂ → F
z w : ℂ
r : ℝ := dist w z
hd : DiffContOnCl ℂ f (ball z r)
hz : IsMaxOn (norm ∘ f) (closedBall z r) z
hw : w ∈ closedBall z r
hw_lt : ‖f w‖ < ‖f z‖
hr : 0 < r
this : ‖∮ (ζ : ℂ) in C(z, r), (ζ - z)⁻¹ • f ζ‖ < 2 * π * ‖f z‖
A : (∮ (ζ : ℂ) in C(z, r), (ζ - z)⁻¹ • f ζ) = (2 * ↑π * I) • f z
⊢ ‖∮ (ζ : ℂ) in C(z, r), (ζ - z)⁻¹ • f ζ‖ = 2 * π * ‖f z‖

Tactic:
simp [A, norm_smul, Real.pi_pos.le]

Result:
no goals

Proof state:
F : Type v
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℂ F
inst✝ : CompleteSpace F
f : ℂ → F
z w : ℂ
r : ℝ := dist w z
hd : DiffContOnCl ℂ f (ball z r)
hz : IsMaxOn (norm ∘ f) (closedBall z r) z
hw : w ∈ closedBall z r
hw_lt : ‖f w‖ < ‖f z‖
hr : 0 < r
⊢ False

Tactic:
suffices ‖∮ ζ in C(z, r), (ζ - z)⁻¹ • f ζ‖ < 2 * π * ‖f z‖ by
  refine this.ne ?_
  have A : (∮ ζ in C(z, r), (ζ - z)⁻¹ • f ζ) = (2 * π * I : ℂ) • f z :=
    hd.circleIntegral_sub_inv_smul (mem_ball_self hr)
  simp [A, norm_smul, Real.pi_pos.le]

Result:
F : Type v
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℂ F
inst✝ : CompleteSpace F
f : ℂ → F
z w : ℂ
r : ℝ := dist w z
hd : DiffContOnCl ℂ f (ball z r)
hz : IsMaxOn (norm ∘ f) (closedBall z r) z
hw : w ∈ closedBall z r
hw_lt : ‖f w‖ < ‖f z‖
hr : 0 < r
⊢ ‖∮ (ζ : ℂ) in C(z, r), (ζ - z)⁻¹ • f ζ‖ < 2 * π * ‖f z‖

Proof state:
F : Type v
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℂ F
inst✝ : CompleteSpace F
f : ℂ → F
z w : ℂ
hd : DiffContOnCl ℂ f (ball z (dist w z))
hz : IsMaxOn (norm ∘ f) (closedBall z (dist w z)) z
⊢ ‖f w‖ = ‖f z‖

Tactic:
set r : ℝ := dist w z

Result:
F : Type v
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℂ F
inst✝ : CompleteSpace F
f : ℂ → F
z w : ℂ
r : ℝ := dist w z
hd : DiffContOnCl ℂ f (ball z r)
hz : IsMaxOn (norm ∘ f) (closedBall z r) z
⊢ ‖f w‖ = ‖f z‖

Proof state:
case refine_2
F : Type v
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℂ F
inst✝ : CompleteSpace F
f : ℂ → F
z w : ℂ
r : ℝ := dist w z
hd : DiffContOnCl ℂ f (ball z r)
hz : IsMaxOn (norm ∘ f) (closedBall z r) z
hw : w ∈ closedBall z r
hw_lt : ‖f w‖ < ‖f z‖
hr : 0 < r
hsub : sphere z r ⊆ closedBall z r
ζ : ℂ
hζ : ‖ζ - z‖ = r
⊢ ‖f ζ‖ ≤ ‖f z‖

Tactic:
exact hz (hsub hζ)

Result:
no goals

Proof state:
F : Type v
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℂ F
inst✝ : CompleteSpace F
f : ℂ → F
z w : ℂ
r : ℝ := dist w z
hd : DiffContOnCl ℂ f (ball z r)
hz : IsMaxOn (norm ∘ f) (closedBall z r) z
hw : w ∈ closedBall z r
⊢ ‖f w‖ = ‖f z‖

Tactic:
refine (isMaxOn_iff.1 hz _ hw).antisymm (not_lt.1 ?_)

Result:
F : Type v
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℂ F
inst✝ : CompleteSpace F
f : ℂ → F
z w : ℂ
r : ℝ := dist w z
hd : DiffContOnCl ℂ f (ball z r)
hz : IsMaxOn (norm ∘ f) (closedBall z r) z
hw : w ∈ closedBall z r
⊢ ¬(norm ∘ f) w < (norm ∘ f) z