-- Mathlib/MeasureTheory/Function/AEEqOfIntegral.lean
theorem AEFinStronglyMeasurable.ae_eq_zero_of_forall_setIntegral_eq_zero {f : α → E}
    (hf_int_finite : ∀ s, MeasurableSet s → μ s < ∞ → IntegrableOn f s μ)
    (hf_zero : ∀ s : Set α, MeasurableSet s → μ s < ∞ → ∫ x in s, f x ∂μ = 0)
    (hf : AEFinStronglyMeasurable f μ) : f =ᵐ[μ] 0

Proof state:
case refine_1
α : Type u_1
E : Type u_2
m0 : MeasurableSpace α
μ : Measure α
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℝ E
inst✝ : CompleteSpace E
f : α → E
hf_int_finite : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → IntegrableOn f s μ
hf_zero : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → ∫ (x : α) in s, f x ∂μ = 0
hf : AEFinStronglyMeasurable f μ
t : Set α := hf.sigmaFiniteSet
this : SigmaFinite (μ.restrict t)
s : Set α
hs : MeasurableSet s
hμs : μ (s ∩ t) < ⊤
⊢ Integrable f (μ.restrict (s ∩ t))

Tactic:
exact hf_int_finite _ (hs.inter hf.measurableSet) hμs

Result:
no goals

Proof state:
case refine_2
α : Type u_1
E : Type u_2
m0 : MeasurableSpace α
μ : Measure α
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℝ E
inst✝ : CompleteSpace E
f : α → E
hf_int_finite : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → IntegrableOn f s μ
hf_zero : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → ∫ (x : α) in s, f x ∂μ = 0
hf : AEFinStronglyMeasurable f μ
t : Set α := hf.sigmaFiniteSet
this : SigmaFinite (μ.restrict t)
⊢ ∀ (s : Set α), MeasurableSet s → (μ.restrict t) s < ⊤ → ∫ (x : α) in s, f x ∂μ.restrict t = 0

Tactic:
intro s hs hμs

Result:
case refine_2
α : Type u_1
E : Type u_2
m0 : MeasurableSpace α
μ : Measure α
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℝ E
inst✝ : CompleteSpace E
f : α → E
hf_int_finite : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → IntegrableOn f s μ
hf_zero : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → ∫ (x : α) in s, f x ∂μ = 0
hf : AEFinStronglyMeasurable f μ
t : Set α := hf.sigmaFiniteSet
this : SigmaFinite (μ.restrict t)
s : Set α
hs : MeasurableSet s
hμs : (μ.restrict t) s < ⊤
⊢ ∫ (x : α) in s, f x ∂μ.restrict t = 0

Proof state:
case refine_2
α : Type u_1
E : Type u_2
m0 : MeasurableSpace α
μ : Measure α
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℝ E
inst✝ : CompleteSpace E
f : α → E
hf_int_finite : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → IntegrableOn f s μ
hf_zero : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → ∫ (x : α) in s, f x ∂μ = 0
hf : AEFinStronglyMeasurable f μ
t : Set α := hf.sigmaFiniteSet
this : SigmaFinite (μ.restrict t)
s : Set α
hs : MeasurableSet s
hμs : (μ.restrict t) s < ⊤
⊢ ∫ (x : α) in s ∩ t, f x ∂μ = 0

Tactic:
rw [Measure.restrict_apply hs] at hμs

Result:
case refine_2
α : Type u_1
E : Type u_2
m0 : MeasurableSpace α
μ : Measure α
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℝ E
inst✝ : CompleteSpace E
f : α → E
hf_int_finite : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → IntegrableOn f s μ
hf_zero : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → ∫ (x : α) in s, f x ∂μ = 0
hf : AEFinStronglyMeasurable f μ
t : Set α := hf.sigmaFiniteSet
this : SigmaFinite (μ.restrict t)
s : Set α
hs : MeasurableSet s
hμs : μ (s ∩ t) < ⊤
⊢ ∫ (x : α) in s ∩ t, f x ∂μ = 0

Proof state:
case refine_1
α : Type u_1
E : Type u_2
m0 : MeasurableSpace α
μ : Measure α
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℝ E
inst✝ : CompleteSpace E
f : α → E
hf_int_finite : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → IntegrableOn f s μ
hf_zero : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → ∫ (x : α) in s, f x ∂μ = 0
hf : AEFinStronglyMeasurable f μ
t : Set α := hf.sigmaFiniteSet
this : SigmaFinite (μ.restrict t)
⊢ ∀ (s : Set α), MeasurableSet s → (μ.restrict t) s < ⊤ → IntegrableOn f s (μ.restrict t)

Tactic:
intro s hs hμs

Result:
case refine_1
α : Type u_1
E : Type u_2
m0 : MeasurableSpace α
μ : Measure α
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℝ E
inst✝ : CompleteSpace E
f : α → E
hf_int_finite : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → IntegrableOn f s μ
hf_zero : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → ∫ (x : α) in s, f x ∂μ = 0
hf : AEFinStronglyMeasurable f μ
t : Set α := hf.sigmaFiniteSet
this : SigmaFinite (μ.restrict t)
s : Set α
hs : MeasurableSet s
hμs : (μ.restrict t) s < ⊤
⊢ IntegrableOn f s (μ.restrict t)

Proof state:
α : Type u_1
E : Type u_2
m0 : MeasurableSpace α
μ : Measure α
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℝ E
inst✝ : CompleteSpace E
f : α → E
hf_int_finite : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → IntegrableOn f s μ
hf_zero : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → ∫ (x : α) in s, f x ∂μ = 0
hf : AEFinStronglyMeasurable f μ
t : Set α := hf.sigmaFiniteSet
⊢ f =ᶠ[ae μ] 0

Tactic:
suffices f =ᵐ[μ.restrict t] 0 from
  ae_of_ae_restrict_of_ae_restrict_compl _ this hf.ae_eq_zero_compl

Result:
α : Type u_1
E : Type u_2
m0 : MeasurableSpace α
μ : Measure α
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℝ E
inst✝ : CompleteSpace E
f : α → E
hf_int_finite : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → IntegrableOn f s μ
hf_zero : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → ∫ (x : α) in s, f x ∂μ = 0
hf : AEFinStronglyMeasurable f μ
t : Set α := hf.sigmaFiniteSet
⊢ f =ᶠ[ae (μ.restrict t)] 0