Theorem: MeasureTheory.Measure.rnDeriv_add_right_of_absolutelyContinuous_of_mutuallySingular
File: Mathlib/MeasureTheory/Decomposition/RadonNikodym.lean

Proof steps:
state_before: α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ ν ν' : Measure α
inst✝² : SigmaFinite μ
inst✝¹ : SigmaFinite ν
inst✝ : SigmaFinite ν'
hμν : μ ≪ ν
hνν' : ν ⟂ₘ ν'
⊢ μ.rnDeriv (ν + ν') =ᶠ[ae ν] μ.rnDeriv ν
state_after: α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ ν ν' : Measure α
inst✝² : SigmaFinite μ
inst✝¹ : SigmaFinite ν
inst✝ : SigmaFinite ν'
hμν : μ ≪ ν
hνν' : ν ⟂ₘ ν'
t : Set α := hνν'.nullSet
⊢ μ.rnDeriv (ν + ν') =ᶠ[ae ν] μ.rnDeriv ν
tactic: let t := hνν'.nullSet
state_before: α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ ν ν' : Measure α
inst✝² : SigmaFinite μ
inst✝¹ : SigmaFinite ν
inst✝ : SigmaFinite ν'
hμν : μ ≪ ν
hνν' : ν ⟂ₘ ν'
t : Set α := hνν'.nullSet
⊢ μ.rnDeriv (ν + ν') =ᶠ[ae ν] μ.rnDeriv ν
state_after: α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ ν ν' : Measure α
inst✝² : SigmaFinite μ
inst✝¹ : SigmaFinite ν
inst✝ : SigmaFinite ν'
hμν : μ ≪ ν
hνν' : ν ⟂ₘ ν'
t : Set α := hνν'.nullSet
ht : MeasurableSet t
⊢ μ.rnDeriv (ν + ν') =ᶠ[ae ν] μ.rnDeriv ν
tactic: have ht : MeasurableSet t := hνν'.measurableSet_nullSet
state_before: α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ ν ν' : Measure α
inst✝² : SigmaFinite μ
inst✝¹ : SigmaFinite ν
inst✝ : SigmaFinite ν'
hμν : μ ≪ ν
hνν' : ν ⟂ₘ ν'
t : Set α := hνν'.nullSet
ht : MeasurableSet t
⊢ μ.rnDeriv (ν + ν') =ᶠ[ae ν] μ.rnDeriv ν
state_after: α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ ν ν' : Measure α
inst✝² : SigmaFinite μ
inst✝¹ : SigmaFinite ν
inst✝ : SigmaFinite ν'
hμν : μ ≪ ν
hνν' : ν ⟂ₘ ν'
t : Set α := hνν'.nullSet
ht : MeasurableSet t
⊢ ∀ᵐ (x : α) ∂ν.restrict tᶜ, μ.rnDeriv (ν + ν') x = μ.rnDeriv ν x
tactic: refine ae_of_ae_restrict_of_ae_restrict_compl t (by simp [t]) ?_
state_before: α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ ν ν' : Measure α
inst✝² : SigmaFinite μ
inst✝¹ : SigmaFinite ν
inst✝ : SigmaFinite ν'
hμν : μ ≪ ν
hνν' : ν ⟂ₘ ν'
t : Set α := hνν'.nullSet
ht : MeasurableSet t
⊢ ∀ᵐ (x : α) ∂ν.restrict tᶜ, μ.rnDeriv (ν + ν') x = μ.rnDeriv ν x
state_after: α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ ν ν' : Measure α
inst✝² : SigmaFinite μ
inst✝¹ : SigmaFinite ν
inst✝ : SigmaFinite ν'
hμν : μ ≪ ν
hνν' : ν ⟂ₘ ν'
t : Set α := hνν'.nullSet
ht : MeasurableSet t
⊢ μ.rnDeriv (ν + ν') =ᶠ[ae (ν.restrict tᶜ)] μ.rnDeriv ν
tactic: change μ.rnDeriv (ν + ν') =ᵐ[ν.restrict tᶜ] μ.rnDeriv ν
state_before: α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ ν ν' : Measure α
inst✝² : SigmaFinite μ
inst✝¹ : SigmaFinite ν
inst✝ : SigmaFinite ν'
hμν : μ ≪ ν
hνν' : ν ⟂ₘ ν'
t : Set α := hνν'.nullSet
ht : MeasurableSet t
⊢ μ.rnDeriv (ν + ν') =ᶠ[ae (ν.restrict tᶜ)] μ.rnDeriv ν
state_after: α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ ν ν' : Measure α
inst✝² : SigmaFinite μ
inst✝¹ : SigmaFinite ν
inst✝ : SigmaFinite ν'
hμν : μ ≪ ν
hνν' : ν ⟂ₘ ν'
t : Set α := hνν'.nullSet
ht : MeasurableSet t
⊢ (ν.restrict tᶜ).withDensity (μ.rnDeriv (ν + ν')) = (ν.restrict tᶜ).withDensity (μ.rnDeriv ν)
tactic: rw [← withDensity_eq_iff_of_sigmaFinite (μ := ν.restrict tᶜ)
    (Measure.measurable_rnDeriv _ _).aemeasurable (Measure.measurable_rnDeriv _ _).aemeasurable]
state_before: α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ ν ν' : Measure α
inst✝² : SigmaFinite μ
inst✝¹ : SigmaFinite ν
inst✝ : SigmaFinite ν'
hμν : μ ≪ ν
hνν' : ν ⟂ₘ ν'
t : Set α := hνν'.nullSet
ht : MeasurableSet t
⊢ (ν.restrict tᶜ).withDensity (μ.rnDeriv (ν + ν')) = (ν.restrict tᶜ).withDensity (μ.rnDeriv ν)
state_after: α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ ν ν' : Measure α
inst✝² : SigmaFinite μ
inst✝¹ : SigmaFinite ν
inst✝ : SigmaFinite ν'
hμν : μ ≪ ν
hνν' : ν ⟂ₘ ν'
t : Set α := hνν'.nullSet
ht : MeasurableSet t
this : (ν.restrict tᶜ).withDensity (μ.rnDeriv (ν + ν')) = ((ν + ν').restrict tᶜ).withDensity (μ.rnDeriv (ν + ν'))
⊢ (ν.restrict tᶜ).withDensity (μ.rnDeriv (ν + ν')) = (ν.restrict tᶜ).withDensity (μ.rnDeriv ν)
tactic: have : (ν.restrict tᶜ).withDensity (μ.rnDeriv (ν + ν'))
      = ((ν + ν').restrict tᶜ).withDensity (μ.rnDeriv (ν + ν')) := by simp [t]
state_before: α : Type u_1
β : Type u_2
m : MeasurableSpace α
μ ν ν' : Measure α
inst✝² : SigmaFinite μ
inst✝¹ : SigmaFinite ν
inst✝ : SigmaFinite ν'
hμν : μ ≪ ν
hνν' : ν ⟂ₘ ν'
t : Set α := hνν'.nullSet
ht : MeasurableSet t
this : (ν.restrict tᶜ).withDensity (μ.rnDeriv (ν + ν')) = ((ν + ν').restrict tᶜ).withDensity (μ.rnDeriv (ν + ν'))
⊢ (ν.restrict tᶜ).withDensity (μ.rnDeriv (ν + ν')) = (ν.restrict tᶜ).withDensity (μ.rnDeriv ν)
state_after: no goals
tactic: rw [this, ← restrict_withDensity ht.compl, ← restrict_withDensity ht.compl,
      Measure.withDensity_rnDeriv_eq _ _ (hμν.add_right ν'), Measure.withDensity_rnDeriv_eq _ _ hμν]