Theorem: MeasureTheory.lintegral_withDensity_eq_lintegral_mul_non_measurable₀
File: Mathlib/MeasureTheory/Measure/WithDensity.lean

tactic: let f' := hf.mk f
state_before: α : Type u_1
m0 : MeasurableSpace α
μ✝ μ : Measure α
f : α → ℝ≥0∞
hf : AEMeasurable f μ
h'f : ∀ᵐ (x : α) ∂μ, f x < ⊤
g : α → ℝ≥0∞
⊢ ∫⁻ (a : α), g a ∂μ.withDensity f = ∫⁻ (a : α), (f * g) a ∂μ
state_after: α : Type u_1
m0 : MeasurableSpace α
μ✝ μ : Measure α
f : α → ℝ≥0∞
hf : AEMeasurable f μ
h'f : ∀ᵐ (x : α) ∂μ, f x < ⊤
g : α → ℝ≥0∞
f' : α → ℝ≥0∞ := AEMeasurable.mk f hf
⊢ ∫⁻ (a : α), g a ∂μ.withDensity f = ∫⁻ (a : α), (f * g) a ∂μ

tactic: calc
  ∫⁻ a, g a ∂μ.withDensity f = ∫⁻ a, g a ∂μ.withDensity f' := by
    rw [withDensity_congr_ae hf.ae_eq_mk]
  _ = ∫⁻ a, (f' * g) a ∂μ := by
    apply lintegral_withDensity_eq_lintegral_mul_non_measurable _ hf.measurable_mk
    filter_upwards [h'f, hf.ae_eq_mk]
    intro x hx h'x
    rwa [← h'x]
  _ = ∫⁻ a, (f * g) a ∂μ := by
    apply lintegral_congr_ae
    filter_upwards [hf.ae_eq_mk]
    intro x hx
    simp only [hx, Pi.mul_apply]
state_before: α : Type u_1
m0 : MeasurableSpace α
μ✝ μ : Measure α
f : α → ℝ≥0∞
hf : AEMeasurable f μ
h'f : ∀ᵐ (x : α) ∂μ, f x < ⊤
g : α → ℝ≥0∞
f' : α → ℝ≥0∞ := AEMeasurable.mk f hf
⊢ ∫⁻ (a : α), g a ∂μ.withDensity f = ∫⁻ (a : α), (f * g) a ∂μ
state_after: no goals

tactic: rw [withDensity_congr_ae hf.ae_eq_mk]
state_before: α : Type u_1
m0 : MeasurableSpace α
μ✝ μ : Measure α
f : α → ℝ≥0∞
hf : AEMeasurable f μ
h'f : ∀ᵐ (x : α) ∂μ, f x < ⊤
g : α → ℝ≥0∞
f' : α → ℝ≥0∞ := AEMeasurable.mk f hf
⊢ ∫⁻ (a : α), g a ∂μ.withDensity f = ∫⁻ (a : α), g a ∂μ.withDensity f'
state_after: no goals

tactic: apply lintegral_withDensity_eq_lintegral_mul_non_measurable _ hf.measurable_mk
state_before: α : Type u_1
m0 : MeasurableSpace α
μ✝ μ : Measure α
f : α → ℝ≥0∞
hf : AEMeasurable f μ
h'f : ∀ᵐ (x : α) ∂μ, f x < ⊤
g : α → ℝ≥0∞
f' : α → ℝ≥0∞ := AEMeasurable.mk f hf
⊢ ∫⁻ (a : α), g a ∂μ.withDensity f' = ∫⁻ (a : α), (f' * g) a ∂μ
state_after: case hf
α : Type u_1
m0 : MeasurableSpace α
μ✝ μ : Measure α
f : α → ℝ≥0∞
hf : AEMeasurable f μ
h'f : ∀ᵐ (x : α) ∂μ, f x < ⊤
g : α → ℝ≥0∞
f' : α → ℝ≥0∞ := AEMeasurable.mk f hf
⊢ ∀ᵐ (x : α) ∂μ, AEMeasurable.mk f hf x < ⊤

tactic: filter_upwards [h'f, hf.ae_eq_mk]
state_before: case hf
α : Type u_1
m0 : MeasurableSpace α
μ✝ μ : Measure α
f : α → ℝ≥0∞
hf : AEMeasurable f μ
h'f : ∀ᵐ (x : α) ∂μ, f x < ⊤
g : α → ℝ≥0∞
f' : α → ℝ≥0∞ := AEMeasurable.mk f hf
⊢ ∀ᵐ (x : α) ∂μ, AEMeasurable.mk f hf x < ⊤
state_after: case h
α : Type u_1
m0 : MeasurableSpace α
μ✝ μ : Measure α
f : α → ℝ≥0∞
hf : AEMeasurable f μ
h'f : ∀ᵐ (x : α) ∂μ, f x < ⊤
g : α → ℝ≥0∞
f' : α → ℝ≥0∞ := AEMeasurable.mk f hf
⊢ ∀ (a : α), f a < ⊤ → f a = AEMeasurable.mk f hf a → AEMeasurable.mk f hf a < ⊤

tactic: intro x hx h'x
state_before: case h
α : Type u_1
m0 : MeasurableSpace α
μ✝ μ : Measure α
f : α → ℝ≥0∞
hf : AEMeasurable f μ
h'f : ∀ᵐ (x : α) ∂μ, f x < ⊤
g : α → ℝ≥0∞
f' : α → ℝ≥0∞ := AEMeasurable.mk f hf
⊢ ∀ (a : α), f a < ⊤ → f a = AEMeasurable.mk f hf a → AEMeasurable.mk f hf a < ⊤
state_after: case h
α : Type u_1
m0 : MeasurableSpace α
μ✝ μ : Measure α
f : α → ℝ≥0∞
hf : AEMeasurable f μ
h'f : ∀ᵐ (x : α) ∂μ, f x < ⊤
g : α → ℝ≥0∞
f' : α → ℝ≥0∞ := AEMeasurable.mk f hf
x : α
hx : f x < ⊤
h'x : f x = AEMeasurable.mk f hf x
⊢ AEMeasurable.mk f hf x < ⊤

tactic: rwa [← h'x]
state_before: case h
α : Type u_1
m0 : MeasurableSpace α
μ✝ μ : Measure α
f : α → ℝ≥0∞
hf : AEMeasurable f μ
h'f : ∀ᵐ (x : α) ∂μ, f x < ⊤
g : α → ℝ≥0∞
f' : α → ℝ≥0∞ := AEMeasurable.mk f hf
x : α
hx : f x < ⊤
h'x : f x = AEMeasurable.mk f hf x
⊢ AEMeasurable.mk f hf x < ⊤
state_after: no goals

tactic: apply lintegral_congr_ae
state_before: α : Type u_1
m0 : MeasurableSpace α
μ✝ μ : Measure α
f : α → ℝ≥0∞
hf : AEMeasurable f μ
h'f : ∀ᵐ (x : α) ∂μ, f x < ⊤
g : α → ℝ≥0∞
f' : α → ℝ≥0∞ := AEMeasurable.mk f hf
⊢ ∫⁻ (a : α), (f' * g) a ∂μ = ∫⁻ (a : α), (f * g) a ∂μ
state_after: case h
α : Type u_1
m0 : MeasurableSpace α
μ✝ μ : Measure α
f : α → ℝ≥0∞
hf : AEMeasurable f μ
h'f : ∀ᵐ (x : α) ∂μ, f x < ⊤
g : α → ℝ≥0∞
f' : α → ℝ≥0∞ := AEMeasurable.mk f hf
⊢ f' * g =ᶠ[ae μ] f * g

tactic: filter_upwards [hf.ae_eq_mk]
state_before: case h
α : Type u_1
m0 : MeasurableSpace α
μ✝ μ : Measure α
f : α → ℝ≥0∞
hf : AEMeasurable f μ
h'f : ∀ᵐ (x : α) ∂μ, f x < ⊤
g : α → ℝ≥0∞
f' : α → ℝ≥0∞ := AEMeasurable.mk f hf
⊢ f' * g =ᶠ[ae μ] f * g
state_after: case h
α : Type u_1
m0 : MeasurableSpace α
μ✝ μ : Measure α
f : α → ℝ≥0∞
hf : AEMeasurable f μ
h'f : ∀ᵐ (x : α) ∂μ, f x < ⊤
g : α → ℝ≥0∞
f' : α → ℝ≥0∞ := AEMeasurable.mk f hf
⊢ ∀ (a : α), f a = AEMeasurable.mk f hf a → (f' * g) a = (f * g) a

tactic: intro x hx
state_before: case h
α : Type u_1
m0 : MeasurableSpace α
μ✝ μ : Measure α
f : α → ℝ≥0∞
hf : AEMeasurable f μ
h'f : ∀ᵐ (x : α) ∂μ, f x < ⊤
g : α → ℝ≥0∞
f' : α → ℝ≥0∞ := AEMeasurable.mk f hf
⊢ ∀ (a : α), f a = AEMeasurable.mk f hf a → (f' * g) a = (f * g) a
state_after: case h
α : Type u_1
m0 : MeasurableSpace α
μ✝ μ : Measure α
f : α → ℝ≥0∞
hf : AEMeasurable f μ
h'f : ∀ᵐ (x : α) ∂μ, f x < ⊤
g : α → ℝ≥0∞
f' : α → ℝ≥0∞ := AEMeasurable.mk f hf
x : α
hx : f x = AEMeasurable.mk f hf x
⊢ (f' * g) x = (f * g) x

tactic: simp only [hx, Pi.mul_apply]
state_before: case h
α : Type u_1
m0 : MeasurableSpace α
μ✝ μ : Measure α
f : α → ℝ≥0∞
hf : AEMeasurable f μ
h'f : ∀ᵐ (x : α) ∂μ, f x < ⊤
g : α → ℝ≥0∞
f' : α → ℝ≥0∞ := AEMeasurable.mk f hf
x : α
hx : f x = AEMeasurable.mk f hf x
⊢ (f' * g) x = (f * g) x
state_after: no goals