-- Mathlib/MeasureTheory/Covering/Differentiation.lean
theorem ae_tendsto_lintegral_enorm_sub_div_of_integrable {f : α → E} (hf : Integrable f μ) :
    ∀ᵐ x ∂μ, Tendsto (fun a => (∫⁻ y in a, ‖f y - f x‖ₑ ∂μ) / μ a) (v.filterAt x) (𝓝 0)

Proof state:
case e_a.h.h
α : Type u_1
inst✝⁴ : PseudoMetricSpace α
m0 : MeasurableSpace α
μ : Measure α
v : VitaliFamily μ
E : Type u_2
inst✝³ : NormedAddCommGroup E
inst✝² : SecondCountableTopology α
inst✝¹ : BorelSpace α
inst✝ : IsLocallyFiniteMeasure μ
f : α → E
hf : Integrable f μ
I : Integrable (AEStronglyMeasurable.mk f ⋯) μ
x : α
hx :
  Tendsto (fun a => (∫⁻ (y : α) in a, ‖AEStronglyMeasurable.mk f ⋯ y - AEStronglyMeasurable.mk f ⋯ x‖ₑ ∂μ) / μ a)
    (v.filterAt x) (𝓝 0)
h'x : f x = AEStronglyMeasurable.mk f ⋯ x
a : Set α
⊢ ∀ᵐ (x_1 : α) ∂μ,
    (fun a => ‖AEStronglyMeasurable.mk f ⋯ a - AEStronglyMeasurable.mk f ⋯ x‖ₑ) x_1 = (fun a => ‖f a - f x‖ₑ) x_1

Tactic:
filter_upwards [hf.1.ae_eq_mk] with y hy

Result:
case h
α : Type u_1
inst✝⁴ : PseudoMetricSpace α
m0 : MeasurableSpace α
μ : Measure α
v : VitaliFamily μ
E : Type u_2
inst✝³ : NormedAddCommGroup E
inst✝² : SecondCountableTopology α
inst✝¹ : BorelSpace α
inst✝ : IsLocallyFiniteMeasure μ
f : α → E
hf : Integrable f μ
I : Integrable (AEStronglyMeasurable.mk f ⋯) μ
x : α
hx :
  Tendsto (fun a => (∫⁻ (y : α) in a, ‖AEStronglyMeasurable.mk f ⋯ y - AEStronglyMeasurable.mk f ⋯ x‖ₑ ∂μ) / μ a)
    (v.filterAt x) (𝓝 0)
h'x : f x = AEStronglyMeasurable.mk f ⋯ x
a : Set α
y : α
hy : f y = AEStronglyMeasurable.mk f ⋯ y
⊢ ‖AEStronglyMeasurable.mk f ⋯ y - AEStronglyMeasurable.mk f ⋯ x‖ₑ = ‖f y - f x‖ₑ

Proof state:
case h
α : Type u_1
inst✝⁴ : PseudoMetricSpace α
m0 : MeasurableSpace α
μ : Measure α
v : VitaliFamily μ
E : Type u_2
inst✝³ : NormedAddCommGroup E
inst✝² : SecondCountableTopology α
inst✝¹ : BorelSpace α
inst✝ : IsLocallyFiniteMeasure μ
f : α → E
hf : Integrable f μ
I : Integrable (AEStronglyMeasurable.mk f ⋯) μ
x : α
hx :
  Tendsto (fun a => (∫⁻ (y : α) in a, ‖AEStronglyMeasurable.mk f ⋯ y - AEStronglyMeasurable.mk f ⋯ x‖ₑ ∂μ) / μ a)
    (v.filterAt x) (𝓝 0)
h'x : f x = AEStronglyMeasurable.mk f ⋯ x
⊢ Tendsto (fun a => (∫⁻ (y : α) in a, ‖f y - f x‖ₑ ∂μ) / μ a) (v.filterAt x) (𝓝 0)

Tactic:
apply hx.congr _

Result:
α : Type u_1
inst✝⁴ : PseudoMetricSpace α
m0 : MeasurableSpace α
μ : Measure α
v : VitaliFamily μ
E : Type u_2
inst✝³ : NormedAddCommGroup E
inst✝² : SecondCountableTopology α
inst✝¹ : BorelSpace α
inst✝ : IsLocallyFiniteMeasure μ
f : α → E
hf : Integrable f μ
I : Integrable (AEStronglyMeasurable.mk f ⋯) μ
x : α
hx :
  Tendsto (fun a => (∫⁻ (y : α) in a, ‖AEStronglyMeasurable.mk f ⋯ y - AEStronglyMeasurable.mk f ⋯ x‖ₑ ∂μ) / μ a)
    (v.filterAt x) (𝓝 0)
h'x : f x = AEStronglyMeasurable.mk f ⋯ x
⊢ ∀ (x_1 : Set α),
    (∫⁻ (y : α) in x_1, ‖AEStronglyMeasurable.mk f ⋯ y - AEStronglyMeasurable.mk f ⋯ x‖ₑ ∂μ) / μ x_1 =
      (∫⁻ (y : α) in x_1, ‖f y - f x‖ₑ ∂μ) / μ x_1

Proof state:
case e_a.h
α : Type u_1
inst✝⁴ : PseudoMetricSpace α
m0 : MeasurableSpace α
μ : Measure α
v : VitaliFamily μ
E : Type u_2
inst✝³ : NormedAddCommGroup E
inst✝² : SecondCountableTopology α
inst✝¹ : BorelSpace α
inst✝ : IsLocallyFiniteMeasure μ
f : α → E
hf : Integrable f μ
I : Integrable (AEStronglyMeasurable.mk f ⋯) μ
x : α
hx :
  Tendsto (fun a => (∫⁻ (y : α) in a, ‖AEStronglyMeasurable.mk f ⋯ y - AEStronglyMeasurable.mk f ⋯ x‖ₑ ∂μ) / μ a)
    (v.filterAt x) (𝓝 0)
h'x : f x = AEStronglyMeasurable.mk f ⋯ x
a : Set α
⊢ (fun a => ‖AEStronglyMeasurable.mk f ⋯ a - AEStronglyMeasurable.mk f ⋯ x‖ₑ) =ᶠ[ae (μ.restrict a)] fun a =>
    ‖f a - f x‖ₑ

Tactic:
apply ae_restrict_of_ae

Result:
case e_a.h.h
α : Type u_1
inst✝⁴ : PseudoMetricSpace α
m0 : MeasurableSpace α
μ : Measure α
v : VitaliFamily μ
E : Type u_2
inst✝³ : NormedAddCommGroup E
inst✝² : SecondCountableTopology α
inst✝¹ : BorelSpace α
inst✝ : IsLocallyFiniteMeasure μ
f : α → E
hf : Integrable f μ
I : Integrable (AEStronglyMeasurable.mk f ⋯) μ
x : α
hx :
  Tendsto (fun a => (∫⁻ (y : α) in a, ‖AEStronglyMeasurable.mk f ⋯ y - AEStronglyMeasurable.mk f ⋯ x‖ₑ ∂μ) / μ a)
    (v.filterAt x) (𝓝 0)
h'x : f x = AEStronglyMeasurable.mk f ⋯ x
a : Set α
⊢ ∀ᵐ (x_1 : α) ∂μ,
    (fun a => ‖AEStronglyMeasurable.mk f ⋯ a - AEStronglyMeasurable.mk f ⋯ x‖ₑ) x_1 = (fun a => ‖f a - f x‖ₑ) x_1