Theorem: MeasureTheory.Measure.rnDeriv_add'
File: Mathlib/MeasureTheory/Decomposition/Lebesgue.lean

tactic: rw [← withDensity_eq_iff_of_sigmaFinite]
state_before: α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ✝ ν ν₁ ν₂ μ : Measure α
inst✝² : SigmaFinite ν₁
inst✝¹ : SigmaFinite ν₂
inst✝ : SigmaFinite μ
⊢ (ν₁ + ν₂).rnDeriv μ =ᶠ[ae μ] ν₁.rnDeriv μ + ν₂.rnDeriv μ
state_after: α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ✝ ν ν₁ ν₂ μ : Measure α
inst✝² : SigmaFinite ν₁
inst✝¹ : SigmaFinite ν₂
inst✝ : SigmaFinite μ
⊢ μ.withDensity ((ν₁ + ν₂).rnDeriv μ) = μ.withDensity (ν₁.rnDeriv μ + ν₂.rnDeriv μ)

case hf
α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ✝ ν ν₁ ν₂ μ : Measure α
inst✝² : SigmaFinite ν₁
inst✝¹ : SigmaFinite ν₂
inst✝ : SigmaFinite μ
⊢ AEMeasurable ((ν₁ + ν₂).rnDeriv μ) μ

case hg
α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ✝ ν ν₁ ν₂ μ : Measure α
inst✝² : SigmaFinite ν₁
inst✝¹ : SigmaFinite ν₂
inst✝ : SigmaFinite μ
⊢ AEMeasurable (ν₁.rnDeriv μ + ν₂.rnDeriv μ) μ

tactic: suffices (ν₁ + ν₂).singularPart μ + μ.withDensity ((ν₁ + ν₂).rnDeriv μ)
    = (ν₁ + ν₂).singularPart μ + μ.withDensity (ν₁.rnDeriv μ + ν₂.rnDeriv μ) by
  rwa [add_right_inj] at this
state_before: α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ✝ ν ν₁ ν₂ μ : Measure α
inst✝² : SigmaFinite ν₁
inst✝¹ : SigmaFinite ν₂
inst✝ : SigmaFinite μ
⊢ μ.withDensity ((ν₁ + ν₂).rnDeriv μ) = μ.withDensity (ν₁.rnDeriv μ + ν₂.rnDeriv μ)
state_after: α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ✝ ν ν₁ ν₂ μ : Measure α
inst✝² : SigmaFinite ν₁
inst✝¹ : SigmaFinite ν₂
inst✝ : SigmaFinite μ
⊢ (ν₁ + ν₂).singularPart μ + μ.withDensity ((ν₁ + ν₂).rnDeriv μ) =
    (ν₁ + ν₂).singularPart μ + μ.withDensity (ν₁.rnDeriv μ + ν₂.rnDeriv μ)

tactic: rw [← (ν₁ + ν₂).haveLebesgueDecomposition_add μ, singularPart_add,
  withDensity_add_left (measurable_rnDeriv _ _), add_assoc,
  add_comm (ν₂.singularPart μ), add_assoc, add_comm _ (ν₂.singularPart μ),
  ← ν₂.haveLebesgueDecomposition_add μ, ← add_assoc, ← ν₁.haveLebesgueDecomposition_add μ]
state_before: α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ✝ ν ν₁ ν₂ μ : Measure α
inst✝² : SigmaFinite ν₁
inst✝¹ : SigmaFinite ν₂
inst✝ : SigmaFinite μ
⊢ (ν₁ + ν₂).singularPart μ + μ.withDensity ((ν₁ + ν₂).rnDeriv μ) =
    (ν₁ + ν₂).singularPart μ + μ.withDensity (ν₁.rnDeriv μ + ν₂.rnDeriv μ)
state_after: no goals

tactic: rwa [add_right_inj] at this
state_before: α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ✝ ν ν₁ ν₂ μ : Measure α
inst✝² : SigmaFinite ν₁
inst✝¹ : SigmaFinite ν₂
inst✝ : SigmaFinite μ
this :
  (ν₁ + ν₂).singularPart μ + μ.withDensity ((ν₁ + ν₂).rnDeriv μ) =
    (ν₁ + ν₂).singularPart μ + μ.withDensity (ν₁.rnDeriv μ + ν₂.rnDeriv μ)
⊢ μ.withDensity ((ν₁ + ν₂).rnDeriv μ) = μ.withDensity (ν₁.rnDeriv μ + ν₂.rnDeriv μ)
state_after: no goals

tactic: exact (measurable_rnDeriv _ _).aemeasurable
state_before: case hf
α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ✝ ν ν₁ ν₂ μ : Measure α
inst✝² : SigmaFinite ν₁
inst✝¹ : SigmaFinite ν₂
inst✝ : SigmaFinite μ
⊢ AEMeasurable ((ν₁ + ν₂).rnDeriv μ) μ
state_after: no goals

tactic: exact ((measurable_rnDeriv _ _).add (measurable_rnDeriv _ _)).aemeasurable
state_before: case hg
α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ✝ ν ν₁ ν₂ μ : Measure α
inst✝² : SigmaFinite ν₁
inst✝¹ : SigmaFinite ν₂
inst✝ : SigmaFinite μ
⊢ AEMeasurable (ν₁.rnDeriv μ + ν₂.rnDeriv μ) μ
state_after: no goals