-- Mathlib/MeasureTheory/Function/AEEqOfIntegral.lean
theorem ae_eq_zero_of_forall_setIntegral_eq_of_finStronglyMeasurable_trim (hm : m ≤ m0) {f : α → E}
    (hf_int_finite : ∀ s, MeasurableSet[m] s → μ s < ∞ → IntegrableOn f s μ)
    (hf_zero : ∀ s : Set α, MeasurableSet[m] s → μ s < ∞ → ∫ x in s, f x ∂μ = 0)
    (hf : FinStronglyMeasurable f (μ.trim hm)) : f =ᵐ[μ] 0

Proof state:
α : Type u_1
E : Type u_2
m m0 : MeasurableSpace α
μ : Measure α
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℝ E
inst✝ : CompleteSpace E
hm : m ≤ m0
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 : FinStronglyMeasurable f (μ.trim hm)
⊢ f =ᶠ[ae μ] 0

Tactic:
obtain ⟨t, ht_meas, htf_zero, htμ⟩ := hf.exists_set_sigmaFinite

Result:
case intro.intro.intro
α : Type u_1
E : Type u_2
m m0 : MeasurableSpace α
μ : Measure α
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℝ E
inst✝ : CompleteSpace E
hm : m ≤ m0
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 : FinStronglyMeasurable f (μ.trim hm)
t : Set α
ht_meas : MeasurableSet t
htf_zero : ∀ x ∈ tᶜ, f x = 0
htμ : SigmaFinite ((μ.trim hm).restrict t)
⊢ f =ᶠ[ae μ] 0

Proof state:
case intro.intro.intro.refine_1
α : Type u_1
E : Type u_2
m m0 : MeasurableSpace α
μ : Measure α
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℝ E
inst✝ : CompleteSpace E
hm : m ≤ m0
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 : FinStronglyMeasurable f (μ.trim hm)
t : Set α
ht_meas : MeasurableSet t
htf_zero✝ : ∀ x ∈ tᶜ, f x = 0
htμ : SigmaFinite ((μ.trim hm).restrict t)
this : SigmaFinite ((μ.restrict t).trim hm)
htf_zero : f =ᶠ[ae (μ.restrict tᶜ)] 0
hf_meas_m : StronglyMeasurable f
s : Set α
hs : MeasurableSet s
hμs : ((μ.restrict t).trim hm) s < ⊤
⊢ IntegrableOn f s ((μ.restrict t).trim hm)

Tactic:
unfold IntegrableOn

Result:
case intro.intro.intro.refine_1
α : Type u_1
E : Type u_2
m m0 : MeasurableSpace α
μ : Measure α
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℝ E
inst✝ : CompleteSpace E
hm : m ≤ m0
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 : FinStronglyMeasurable f (μ.trim hm)
t : Set α
ht_meas : MeasurableSet t
htf_zero✝ : ∀ x ∈ tᶜ, f x = 0
htμ : SigmaFinite ((μ.trim hm).restrict t)
this : SigmaFinite ((μ.restrict t).trim hm)
htf_zero : f =ᶠ[ae (μ.restrict tᶜ)] 0
hf_meas_m : StronglyMeasurable f
s : Set α
hs : MeasurableSet s
hμs : ((μ.restrict t).trim hm) s < ⊤
⊢ Integrable f (((μ.restrict t).trim hm).restrict s)

Proof state:
case intro.intro.intro.refine_2
α : Type u_1
E : Type u_2
m m0 : MeasurableSpace α
μ : Measure α
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℝ E
inst✝ : CompleteSpace E
hm : m ≤ m0
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 : FinStronglyMeasurable f (μ.trim hm)
t : Set α
ht_meas : MeasurableSet t
htf_zero✝ : ∀ x ∈ tᶜ, f x = 0
htμ : SigmaFinite ((μ.trim hm).restrict t)
this : SigmaFinite ((μ.restrict t).trim hm)
htf_zero : f =ᶠ[ae (μ.restrict tᶜ)] 0
hf_meas_m : StronglyMeasurable f
s : Set α
hs : MeasurableSet s
hμs : μ (s ∩ t) < ⊤
⊢ ∫ (x : α) in s ∩ t, f x ∂μ = 0

Tactic:
exact hf_zero _ (hs.inter ht_meas) hμs

Result:
no goals

Proof state:
case intro.intro.intro.refine_1
α : Type u_1
E : Type u_2
m m0 : MeasurableSpace α
μ : Measure α
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℝ E
inst✝ : CompleteSpace E
hm : m ≤ m0
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 : FinStronglyMeasurable f (μ.trim hm)
t : Set α
ht_meas : MeasurableSet t
htf_zero✝ : ∀ x ∈ tᶜ, f x = 0
htμ : SigmaFinite ((μ.trim hm).restrict t)
this : SigmaFinite ((μ.restrict t).trim hm)
htf_zero : f =ᶠ[ae (μ.restrict tᶜ)] 0
hf_meas_m : StronglyMeasurable f
s : Set α
hs : MeasurableSet s
hμs : ((μ.restrict t).trim hm) s < ⊤
⊢ Integrable f ((μ.restrict (s ∩ t)).trim hm)

Tactic:
rw [← restrict_trim hm μ ht_meas, Measure.restrict_apply hs,
  trim_measurableSet_eq hm (hs.inter ht_meas)] at hμs

Result:
case intro.intro.intro.refine_1
α : Type u_1
E : Type u_2
m m0 : MeasurableSpace α
μ : Measure α
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℝ E
inst✝ : CompleteSpace E
hm : m ≤ m0
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 : FinStronglyMeasurable f (μ.trim hm)
t : Set α
ht_meas : MeasurableSet t
htf_zero✝ : ∀ x ∈ tᶜ, f x = 0
htμ : SigmaFinite ((μ.trim hm).restrict t)
this : SigmaFinite ((μ.restrict t).trim hm)
htf_zero : f =ᶠ[ae (μ.restrict tᶜ)] 0
hf_meas_m : StronglyMeasurable f
s : Set α
hs : MeasurableSet s
hμs : μ (s ∩ t) < ⊤
⊢ Integrable f ((μ.restrict (s ∩ t)).trim hm)

Proof state:
case intro.intro.intro.refine_1
α : Type u_1
E : Type u_2
m m0 : MeasurableSpace α
μ : Measure α
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℝ E
inst✝ : CompleteSpace E
hm : m ≤ m0
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 : FinStronglyMeasurable f (μ.trim hm)
t : Set α
ht_meas : MeasurableSet t
htf_zero✝ : ∀ x ∈ tᶜ, f x = 0
htμ : SigmaFinite ((μ.trim hm).restrict t)
this : SigmaFinite ((μ.restrict t).trim hm)
htf_zero : f =ᶠ[ae (μ.restrict tᶜ)] 0
hf_meas_m : StronglyMeasurable f
s : Set α
hs : MeasurableSet s
hμs : μ (s ∩ t) < ⊤
⊢ Integrable f ((μ.restrict (s ∩ t)).trim hm)

Tactic:
refine Integrable.trim hm ?_ hf_meas_m

Result:
case intro.intro.intro.refine_1
α : Type u_1
E : Type u_2
m m0 : MeasurableSpace α
μ : Measure α
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℝ E
inst✝ : CompleteSpace E
hm : m ≤ m0
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 : FinStronglyMeasurable f (μ.trim hm)
t : Set α
ht_meas : MeasurableSet t
htf_zero✝ : ∀ x ∈ tᶜ, f x = 0
htμ : SigmaFinite ((μ.trim hm).restrict t)
this : SigmaFinite ((μ.restrict t).trim hm)
htf_zero : f =ᶠ[ae (μ.restrict tᶜ)] 0
hf_meas_m : StronglyMeasurable f
s : Set α
hs : MeasurableSet s
hμs : μ (s ∩ t) < ⊤
⊢ Integrable f (μ.restrict (s ∩ t))

Proof state:
case intro.intro.intro
α : Type u_1
E : Type u_2
m m0 : MeasurableSpace α
μ : Measure α
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℝ E
inst✝ : CompleteSpace E
hm : m ≤ m0
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 : FinStronglyMeasurable f (μ.trim hm)
t : Set α
ht_meas : MeasurableSet t
htf_zero : ∀ x ∈ tᶜ, f x = 0
htμ : SigmaFinite ((μ.trim hm).restrict t)
⊢ f =ᶠ[ae μ] 0

Tactic:
haveI : SigmaFinite ((μ.restrict t).trim hm) := by rwa [restrict_trim hm μ ht_meas] at htμ

Result:
case intro.intro.intro
α : Type u_1
E : Type u_2
m m0 : MeasurableSpace α
μ : Measure α
inst✝² : NormedAddCommGroup E
inst✝¹ : NormedSpace ℝ E
inst✝ : CompleteSpace E
hm : m ≤ m0
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 : FinStronglyMeasurable f (μ.trim hm)
t : Set α
ht_meas : MeasurableSet t
htf_zero : ∀ x ∈ tᶜ, f x = 0
htμ : SigmaFinite ((μ.trim hm).restrict t)
this : SigmaFinite ((μ.restrict t).trim hm)
⊢ f =ᶠ[ae μ] 0