theorem ae_eq_of_forall_set_integral_eq_of_sigmaFinite' (hm : m ≤ m0) [SigmaFinite (μ.trim hm)]
    {f g : α → F'} (hf_int_finite : ∀ s, MeasurableSet[m] s → μ s < ∞ → IntegrableOn f s μ)
    (hg_int_finite : ∀ s, MeasurableSet[m] s → μ s < ∞ → IntegrableOn g s μ)
    (hfg_eq : ∀ s : Set α, MeasurableSet[m] s → μ s < ∞ → ∫ x in s, f x ∂μ = ∫ x in s, g x ∂μ)
    (hfm : AEStronglyMeasurable' m f μ) (hgm : AEStronglyMeasurable' m g μ) : f =ᵐ[μ] g := by
  rw [← ae_eq_trim_iff_of_aeStronglyMeasurable' hm hfm hgm]
  have hf_mk_int_finite :
    ∀ s, MeasurableSet[m] s → μ.trim hm s < ∞ → @IntegrableOn _ _ m _ (hfm.mk f) s (μ.trim hm) := by
    intro s hs hμs
    rw [trim_measurableSet_eq hm hs] at hμs
    -- Porting note: `rw [IntegrableOn]` fails with
    -- synthesized type class instance is not definitionally equal to expression inferred by typing
    -- rules, synthesized m0 inferred m
    unfold IntegrableOn
    rw [restrict_trim hm _ hs]
    refine' Integrable.trim hm _ hfm.stronglyMeasurable_mk
    exact Integrable.congr (hf_int_finite s hs hμs) (ae_restrict_of_ae hfm.ae_eq_mk)
  have hg_mk_int_finite :
    ∀ s, MeasurableSet[m] s → μ.trim hm s < ∞ → @IntegrableOn _ _ m _ (hgm.mk g) s (μ.trim hm) := by
    intro s hs hμs
    rw [trim_measurableSet_eq hm hs] at hμs
    -- Porting note: `rw [IntegrableOn]` fails with
    -- synthesized type class instance is not definitionally equal to expression inferred by typing
    -- rules, synthesized m0 inferred m
    unfold IntegrableOn
    rw [restrict_trim hm _ hs]
    refine' Integrable.trim hm _ hgm.stronglyMeasurable_mk
    exact Integrable.congr (hg_int_finite s hs hμs) (ae_restrict_of_ae hgm.ae_eq_mk)
  

Proof state:
α : Type u_1
E' : Type u_2
F' : Type u_3
𝕜 : Type u_4
p : ℝ≥0∞
m m0 : MeasurableSpace α
μ : Measure α
inst✝⁹ : IsROrC 𝕜
inst✝⁸ : NormedAddCommGroup E'
inst✝⁷ : InnerProductSpace 𝕜 E'
inst✝⁶ : CompleteSpace E'
inst✝⁵ : NormedSpace ℝ E'
inst✝⁴ : NormedAddCommGroup F'
inst✝³ : NormedSpace 𝕜 F'
inst✝² : NormedSpace ℝ F'
inst✝¹ : CompleteSpace F'
hm : m ≤ m0
inst✝ : SigmaFinite (Measure.trim μ hm)
f g : α → F'
hf_int_finite : ∀ (s : Set α), MeasurableSet s → ↑↑μ s < ⊤ → IntegrableOn f s
hg_int_finite : ∀ (s : Set α), MeasurableSet s → ↑↑μ s < ⊤ → IntegrableOn g s
hfg_eq : ∀ (s : Set α), MeasurableSet s → ↑↑μ s < ⊤ → ∫ (x : α) in s, f x ∂μ = ∫ (x : α) in s, g x ∂μ
hfm : AEStronglyMeasurable' m f μ
hgm : AEStronglyMeasurable' m g μ
hf_mk_int_finite :
  ∀ (s : Set α), MeasurableSet s → ↑↑(Measure.trim μ hm) s < ⊤ → IntegrableOn (AEStronglyMeasurable'.mk f hfm) s
hg_mk_int_finite :
  ∀ (s : Set α), MeasurableSet s → ↑↑(Measure.trim μ hm) s < ⊤ → IntegrableOn (AEStronglyMeasurable'.mk g hgm) s
⊢ AEStronglyMeasurable'.mk f hfm =ᵐ[Measure.trim μ hm] AEStronglyMeasurable'.mk g hgm

Next tactic:
have hfg_mk_eq :
    ∀ s : Set α,
      MeasurableSet[m] s →
        μ.trim hm s < ∞ → ∫ x in s, hfm.mk f x ∂μ.trim hm = ∫ x in s, hgm.mk g x ∂μ.trim hm := by
    intro s hs hμs
    rw [trim_measurableSet_eq hm hs] at hμs
    rw [restrict_trim hm _ hs, ← integral_trim hm hfm.stronglyMeasurable_mk, ←
      integral_trim hm hgm.stronglyMeasurable_mk,
      integral_congr_ae (ae_restrict_of_ae hfm.ae_eq_mk.symm),
      integral_congr_ae (ae_restrict_of_ae hgm.ae_eq_mk.symm)]
    exact hfg_eq s hs hμs