/-- An auxiliary lemma for
`Complex.circleIntegral_sub_inv_smul_of_differentiable_on_off_countable`. This lemma assumes
`w ∉ s` while the main lemma drops this assumption. -/
theorem circleIntegral_sub_inv_smul_of_differentiable_on_off_countable_aux {R : ℝ} {c w : ℂ}
    {f : ℂ → E} {s : Set ℂ} (hs : s.Countable) (hw : w ∈ ball c R \ s)
    (hc : ContinuousOn f (closedBall c R)) (hd : ∀ x ∈ ball c R \ s, DifferentiableAt ℂ f x) :
    (∮ z in C(c, R), (z - w)⁻¹ • f z) = (2 * π * I : ℂ) • f w := by
  have hR : 0 < R := dist_nonneg.trans_lt hw.1
  set F : ℂ → E := dslope f w
  have hws : (insert w s).Countable := hs.insert w
  have hcF : ContinuousOn F (closedBall c R) :=
    (continuousOn_dslope <| closedBall_mem_nhds_of_mem hw.1).2 ⟨hc, hd _ hw⟩
  have hdF : ∀ z ∈ ball (c : ℂ) R \ insert w s, DifferentiableAt ℂ F z := fun z hz =>
    (differentiableAt_dslope_of_ne (ne_of_mem_of_not_mem (mem_insert _ _) hz.2).symm).2
      (hd _ (diff_subset_diff_right (subset_insert _ _) hz))
  have HI := circleIntegral_eq_zero_of_differentiable_on_off_countable hR.le hws hcF hdF
  have hne : ∀ z ∈ sphere c R, z ≠ w := fun z hz => ne_of_mem_of_not_mem hz (ne_of_lt hw.1)
  have hFeq : EqOn F (fun z => (z - w)⁻¹ • f z - (z - w)⁻¹ • f w) (sphere c R) := fun z hz ↦
    calc
      F z = (z - w)⁻¹ • (f z - f w) := update_noteq (hne z hz) _ _
      _ = (z - w)⁻¹ • f z - (z - w)⁻¹ • f w := smul_sub _ _ _
  have hc' : ContinuousOn (fun z => (z - w)⁻¹) (sphere c R) :=
    (continuousOn_id.sub continuousOn_const).inv₀ fun z hz => sub_ne_zero.2 <| hne z hz
  rw [← circleIntegral.integral_sub_inv_of_mem_ball hw.1, ← circleIntegral.integral_smul_const, ←
    sub_eq_zero, ← circleIntegral.integral_sub, ← circleIntegral.integral_congr hR.le hFeq, HI]
  

Proof state:
case hf
E : Type u
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℂ E
inst✝ : CompleteSpace E
R : ℝ
c w : ℂ
f : ℂ → E
s : Set ℂ
hs : Set.Countable s
hw : w ∈ ball c R \ s
hc : ContinuousOn f (closedBall c R)
hd : ∀ x ∈ ball c R \ s, DifferentiableAt ℂ f x
hR : 0 < R
F : ℂ → E := dslope f w
hws : Set.Countable (insert w s)
hcF : ContinuousOn F (closedBall c R)
hdF : ∀ z ∈ ball c R \ insert w s, DifferentiableAt ℂ F z
HI : (∮ (z : ℂ) in C(c, R), F z) = 0
hne : ∀ z ∈ sphere c R, z ≠ w
hFeq : EqOn F (fun z => (z - w)⁻¹ • f z - (z - w)⁻¹ • f w) (sphere c R)
hc' : ContinuousOn (fun z => (z - w)⁻¹) (sphere c R)
⊢ CircleIntegrable (fun z => (z - w)⁻¹ • f z) c R
case hg
E : Type u
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℂ E
inst✝ : CompleteSpace E
R : ℝ
c w : ℂ
f : ℂ → E
s : Set ℂ
hs : Set.Countable s
hw : w ∈ ball c R \ s
hc : ContinuousOn f (closedBall c R)
hd : ∀ x ∈ ball c R \ s, DifferentiableAt ℂ f x
hR : 0 < R
F : ℂ → E := dslope f w
hws : Set.Countable (insert w s)
hcF : ContinuousOn F (closedBall c R)
hdF : ∀ z ∈ ball c R \ insert w s, DifferentiableAt ℂ F z
HI : (∮ (z : ℂ) in C(c, R), F z) = 0
hne : ∀ z ∈ sphere c R, z ≠ w
hFeq : EqOn F (fun z => (z - w)⁻¹ • f z - (z - w)⁻¹ • f w) (sphere c R)
hc' : ContinuousOn (fun z => (z - w)⁻¹) (sphere c R)
⊢ CircleIntegrable (fun z => (z - w)⁻¹ • f w) c R

Next tactic:
exacts [(hc'.smul (hc.mono sphere_subset_closedBall)).circleIntegrable hR.le,
    (hc'.smul continuousOn_const).circleIntegrable hR.le]