-- Mathlib/Probability/Kernel/RadonNikodym.lean
lemma singularPart_of_subset_mutuallySingularSetSlice [IsFiniteKernel κ]
    [IsFiniteKernel η] {a : α} {s : Set γ} (hsm : MeasurableSet s)
    (hs : s ⊆ mutuallySingularSetSlice κ η a) :
    singularPart κ η a s = κ a s

Proof state:
α : Type u_1
γ : Type u_2
mα : MeasurableSpace α
mγ : MeasurableSpace γ
κ η : Kernel α γ
hαγ : MeasurableSpace.CountableOrCountablyGenerated α γ
inst✝¹ : IsFiniteKernel κ
inst✝ : IsFiniteKernel η
a : α
s : Set γ
hsm : MeasurableSet s
hs : s ⊆ κ.mutuallySingularSetSlice η a
hs' : ∀ x ∈ s, 1 ≤ κ.rnDerivAux (κ + η) a x
⊢ ∫⁻ (x : γ) in s,
      ↑(κ.rnDerivAux (κ + η) a x).toNNReal - ↑(1 - κ.rnDerivAux (κ + η) a x).toNNReal * κ.rnDeriv η a x ∂(κ + η) a =
    ∫⁻ (x : γ) in s, 1 ∂(κ + η) a

Tactic:
refine setLIntegral_congr_fun hsm ?_

Result:
α : Type u_1
γ : Type u_2
mα : MeasurableSpace α
mγ : MeasurableSpace γ
κ η : Kernel α γ
hαγ : MeasurableSpace.CountableOrCountablyGenerated α γ
inst✝¹ : IsFiniteKernel κ
inst✝ : IsFiniteKernel η
a : α
s : Set γ
hsm : MeasurableSet s
hs : s ⊆ κ.mutuallySingularSetSlice η a
hs' : ∀ x ∈ s, 1 ≤ κ.rnDerivAux (κ + η) a x
⊢ ∀ᵐ (x : γ) ∂(κ + η) a,
    x ∈ s → ↑(κ.rnDerivAux (κ + η) a x).toNNReal - ↑(1 - κ.rnDerivAux (κ + η) a x).toNNReal * κ.rnDeriv η a x = 1

Proof state:
α : Type u_1
γ : Type u_2
mα : MeasurableSpace α
mγ : MeasurableSpace γ
κ η : Kernel α γ
hαγ : MeasurableSpace.CountableOrCountablyGenerated α γ
inst✝¹ : IsFiniteKernel κ
inst✝ : IsFiniteKernel η
a : α
s : Set γ
hsm : MeasurableSet s
hs : s ⊆ κ.mutuallySingularSetSlice η a
hs' : ∀ x ∈ s, 1 ≤ κ.rnDerivAux (κ + η) a x
⊢ ∫⁻ (x : γ) in s, 1 ∂(κ + η) a = ((κ + η) a) s

Tactic:
simp

Result:
no goals

Proof state:
α : Type u_1
γ : Type u_2
mα : MeasurableSpace α
mγ : MeasurableSpace γ
κ η : Kernel α γ
hαγ : MeasurableSpace.CountableOrCountablyGenerated α γ
inst✝¹ : IsFiniteKernel κ
inst✝ : IsFiniteKernel η
a : α
s : Set γ
hsm : MeasurableSet s
hs : s ⊆ κ.mutuallySingularSetSlice η a
hs' : ∀ x ∈ s, 1 ≤ κ.rnDerivAux (κ + η) a x
this : (η a) s = 0
⊢ ((κ + η) a) s = (κ a) s

Tactic:
simp [this]

Result:
no goals

Proof state:
α : Type u_1
γ : Type u_2
mα : MeasurableSpace α
mγ : MeasurableSpace γ
κ η : Kernel α γ
hαγ : MeasurableSpace.CountableOrCountablyGenerated α γ
inst✝¹ : IsFiniteKernel κ
inst✝ : IsFiniteKernel η
a : α
s : Set γ
hsm : MeasurableSet s
hs : s ⊆ κ.mutuallySingularSetSlice η a
hs' : ∀ x ∈ s, 1 ≤ κ.rnDerivAux (κ + η) a x
⊢ ∀ᵐ (x : γ) ∂(κ + η) a,
    x ∈ s → ↑(κ.rnDerivAux (κ + η) a x).toNNReal - ↑(1 - κ.rnDerivAux (κ + η) a x).toNNReal * κ.rnDeriv η a x = 1

Tactic:
have h_le : κ ≤ κ + η := le_add_of_nonneg_right bot_le

Result:
α : Type u_1
γ : Type u_2
mα : MeasurableSpace α
mγ : MeasurableSpace γ
κ η : Kernel α γ
hαγ : MeasurableSpace.CountableOrCountablyGenerated α γ
inst✝¹ : IsFiniteKernel κ
inst✝ : IsFiniteKernel η
a : α
s : Set γ
hsm : MeasurableSet s
hs : s ⊆ κ.mutuallySingularSetSlice η a
hs' : ∀ x ∈ s, 1 ≤ κ.rnDerivAux (κ + η) a x
h_le : κ ≤ κ + η
⊢ ∀ᵐ (x : γ) ∂(κ + η) a,
    x ∈ s → ↑(κ.rnDerivAux (κ + η) a x).toNNReal - ↑(1 - κ.rnDerivAux (κ + η) a x).toNNReal * κ.rnDeriv η a x = 1

Proof state:
α : Type u_1
γ : Type u_2
mα : MeasurableSpace α
mγ : MeasurableSpace γ
κ η : Kernel α γ
hαγ : MeasurableSpace.CountableOrCountablyGenerated α γ
inst✝¹ : IsFiniteKernel κ
inst✝ : IsFiniteKernel η
a : α
s : Set γ
hsm : MeasurableSet s
hs : s ⊆ κ.mutuallySingularSetSlice η a
hs' : ∀ x ∈ s, 1 ≤ κ.rnDerivAux (κ + η) a x
⊢ ∫⁻ (b : γ) in s,
      ↑(κ.rnDerivAux (κ + η) a b).toNNReal - ↑(1 - κ.rnDerivAux (κ + η) a b).toNNReal * κ.rnDeriv η a b ∂(κ + η) a =
    (κ a) s

case hf
α : Type u_1
γ : Type u_2
mα : MeasurableSpace α
mγ : MeasurableSpace γ
κ η : Kernel α γ
hαγ : MeasurableSpace.CountableOrCountablyGenerated α γ
inst✝¹ : IsFiniteKernel κ
inst✝ : IsFiniteKernel η
a : α
s : Set γ
hsm : MeasurableSet s
hs : s ⊆ κ.mutuallySingularSetSlice η a
hs' : ∀ x ∈ s, 1 ≤ κ.rnDerivAux (κ + η) a x
⊢ Measurable
    (Function.uncurry fun a x =>
      ↑(κ.rnDerivAux (κ + η) a x).toNNReal - ↑(1 - κ.rnDerivAux (κ + η) a x).toNNReal * κ.rnDeriv η a x)

Tactic:
swap

Result:
case hf
α : Type u_1
γ : Type u_2
mα : MeasurableSpace α
mγ : MeasurableSpace γ
κ η : Kernel α γ
hαγ : MeasurableSpace.CountableOrCountablyGenerated α γ
inst✝¹ : IsFiniteKernel κ
inst✝ : IsFiniteKernel η
a : α
s : Set γ
hsm : MeasurableSet s
hs : s ⊆ κ.mutuallySingularSetSlice η a
hs' : ∀ x ∈ s, 1 ≤ κ.rnDerivAux (κ + η) a x
⊢ Measurable
    (Function.uncurry fun a x =>
      ↑(κ.rnDerivAux (κ + η) a x).toNNReal - ↑(1 - κ.rnDerivAux (κ + η) a x).toNNReal * κ.rnDeriv η a x)

α : Type u_1
γ : Type u_2
mα : MeasurableSpace α
mγ : MeasurableSpace γ
κ η : Kernel α γ
hαγ : MeasurableSpace.CountableOrCountablyGenerated α γ
inst✝¹ : IsFiniteKernel κ
inst✝ : IsFiniteKernel η
a : α
s : Set γ
hsm : MeasurableSet s
hs : s ⊆ κ.mutuallySingularSetSlice η a
hs' : ∀ x ∈ s, 1 ≤ κ.rnDerivAux (κ + η) a x
⊢ ∫⁻ (b : γ) in s,
      ↑(κ.rnDerivAux (κ + η) a b).toNNReal - ↑(1 - κ.rnDerivAux (κ + η) a b).toNNReal * κ.rnDeriv η a b ∂(κ + η) a =
    (κ a) s

Proof state:
α : Type u_1
γ : Type u_2
mα : MeasurableSpace α
mγ : MeasurableSpace γ
κ η : Kernel α γ
hαγ : MeasurableSpace.CountableOrCountablyGenerated α γ
inst✝¹ : IsFiniteKernel κ
inst✝ : IsFiniteKernel η
a : α
s : Set γ
hsm : MeasurableSet s
hs : s ⊆ κ.mutuallySingularSetSlice η a
hs' : ∀ x ∈ s, 1 ≤ κ.rnDerivAux (κ + η) a x
⊢ ((κ + η) a) s = (κ a) s

Tactic:
suffices η a s = 0 by simp [this]

Result:
α : Type u_1
γ : Type u_2
mα : MeasurableSpace α
mγ : MeasurableSpace γ
κ η : Kernel α γ
hαγ : MeasurableSpace.CountableOrCountablyGenerated α γ
inst✝¹ : IsFiniteKernel κ
inst✝ : IsFiniteKernel η
a : α
s : Set γ
hsm : MeasurableSet s
hs : s ⊆ κ.mutuallySingularSetSlice η a
hs' : ∀ x ∈ s, 1 ≤ κ.rnDerivAux (κ + η) a x
⊢ (η a) s = 0

Proof state:
α : Type u_1
γ : Type u_2
mα : MeasurableSpace α
mγ : MeasurableSpace γ
κ η : Kernel α γ
hαγ : MeasurableSpace.CountableOrCountablyGenerated α γ
inst✝¹ : IsFiniteKernel κ
inst✝ : IsFiniteKernel η
a : α
s : Set γ
hsm : MeasurableSet s
hs : s ⊆ κ.mutuallySingularSetSlice η a
⊢ ((κ.singularPart η) a) s = (κ a) s

Tactic:
have hs' : ∀ x ∈ s, 1 ≤ rnDerivAux κ (κ + η) a x := fun _ hx ↦ hs hx

Result:
α : Type u_1
γ : Type u_2
mα : MeasurableSpace α
mγ : MeasurableSpace γ
κ η : Kernel α γ
hαγ : MeasurableSpace.CountableOrCountablyGenerated α γ
inst✝¹ : IsFiniteKernel κ
inst✝ : IsFiniteKernel η
a : α
s : Set γ
hsm : MeasurableSet s
hs : s ⊆ κ.mutuallySingularSetSlice η a
hs' : ∀ x ∈ s, 1 ≤ κ.rnDerivAux (κ + η) a x
⊢ ((κ.singularPart η) a) s = (κ a) s

Proof state:
α : Type u_1
γ : Type u_2
mα : MeasurableSpace α
mγ : MeasurableSpace γ
κ η : Kernel α γ
hαγ : MeasurableSpace.CountableOrCountablyGenerated α γ
inst✝¹ : IsFiniteKernel κ
inst✝ : IsFiniteKernel η
a : α
s : Set γ
hsm : MeasurableSet s
hs : s ⊆ κ.mutuallySingularSetSlice η a
hs' : ∀ x ∈ s, 1 ≤ κ.rnDerivAux (κ + η) a x
⊢ (η a) s = 0

Tactic:
exact measure_mono_null hs (measure_mutuallySingularSetSlice κ η a)

Result:
no goals