-- Mathlib/Probability/Kernel/Disintegration/Density.lean
lemma setIntegral_densityProcess_of_mem (hκν : fst κ ≤ ν) [hν : IsFiniteKernel ν]
    (n : ℕ) (a : α) {s : Set β} (hs : MeasurableSet s) {u : Set γ}
    (hu : u ∈ countablePartition γ n) :
    ∫ x in u, densityProcess κ ν n a x s ∂(ν a) = (κ a (u ×ˢ s)).toReal

Proof state:
case hf
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
inst✝ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
hκν : κ.fst ≤ ν
hν : IsFiniteKernel ν
n : ℕ
a : α
s : Set β
hs : MeasurableSet s
u : Set γ
hu : u ∈ countablePartition γ n
this : IsFiniteKernel κ
hu_meas : MeasurableSet u
x : γ
⊢ (κ a) (countablePartitionSet n x ×ˢ s) / (ν a) (countablePartitionSet n x) < ⊤

Tactic:
by_cases h0 : ν a (countablePartitionSet n x) = 0

Result:
case pos
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
inst✝ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
hκν : κ.fst ≤ ν
hν : IsFiniteKernel ν
n : ℕ
a : α
s : Set β
hs : MeasurableSet s
u : Set γ
hu : u ∈ countablePartition γ n
this : IsFiniteKernel κ
hu_meas : MeasurableSet u
x : γ
h0 : (ν a) (countablePartitionSet n x) = 0
⊢ (κ a) (countablePartitionSet n x ×ˢ s) / (ν a) (countablePartitionSet n x) < ⊤

case neg
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
inst✝ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
hκν : κ.fst ≤ ν
hν : IsFiniteKernel ν
n : ℕ
a : α
s : Set β
hs : MeasurableSet s
u : Set γ
hu : u ∈ countablePartition γ n
this : IsFiniteKernel κ
hu_meas : MeasurableSet u
x : γ
h0 : ¬(ν a) (countablePartitionSet n x) = 0
⊢ (κ a) (countablePartitionSet n x ×ˢ s) / (ν a) (countablePartitionSet n x) < ⊤

Proof state:
case neg
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
inst✝ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
hκν : κ.fst ≤ ν
hν : IsFiniteKernel ν
n : ℕ
a : α
s : Set β
hs : MeasurableSet s
u : Set γ
hu : u ∈ countablePartition γ n
this✝ : IsFiniteKernel κ
hu_meas : MeasurableSet u
this :
  ∫⁻ (x : γ) in u, (κ a) (countablePartitionSet n x ×ˢ s) / (ν a) (countablePartitionSet n x) ∂ν a =
    ∫⁻ (x : γ) in u, (κ a) (u ×ˢ s) / (ν a) u ∂ν a
h0 : ¬(ν a) u = 0
⊢ (κ a) (u ×ˢ s) / (ν a) u * (ν a) u = (κ a) (u ×ˢ s)

Tactic:
rw [div_eq_mul_inv, mul_assoc, ENNReal.inv_mul_cancel h0, mul_one]

Result:
case neg
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
inst✝ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
hκν : κ.fst ≤ ν
hν : IsFiniteKernel ν
n : ℕ
a : α
s : Set β
hs : MeasurableSet s
u : Set γ
hu : u ∈ countablePartition γ n
this✝ : IsFiniteKernel κ
hu_meas : MeasurableSet u
this :
  ∫⁻ (x : γ) in u, (κ a) (countablePartitionSet n x ×ˢ s) / (ν a) (countablePartitionSet n x) ∂ν a =
    ∫⁻ (x : γ) in u, (κ a) (u ×ˢ s) / (ν a) u ∂ν a
h0 : ¬(ν a) u = 0
⊢ (ν a) u ≠ ⊤

Proof state:
case pos
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
inst✝ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
hκν : κ.fst ≤ ν
hν : IsFiniteKernel ν
n : ℕ
a : α
s : Set β
hs : MeasurableSet s
u : Set γ
hu : u ∈ countablePartition γ n
this✝ : IsFiniteKernel κ
hu_meas : MeasurableSet u
this :
  ∫⁻ (x : γ) in u, (κ a) (countablePartitionSet n x ×ˢ s) / (ν a) (countablePartitionSet n x) ∂ν a =
    ∫⁻ (x : γ) in u, (κ a) (u ×ˢ s) / (ν a) u ∂ν a
h0 : (ν a) u = 0
h0' : (κ a) {p | p.1 ∈ u} = 0
⊢ 0 = (κ a) (u ×ˢ s)

Tactic:
refine (measure_mono_null ?_ h0').symm

Result:
case pos
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
inst✝ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
hκν : κ.fst ≤ ν
hν : IsFiniteKernel ν
n : ℕ
a : α
s : Set β
hs : MeasurableSet s
u : Set γ
hu : u ∈ countablePartition γ n
this✝ : IsFiniteKernel κ
hu_meas : MeasurableSet u
this :
  ∫⁻ (x : γ) in u, (κ a) (countablePartitionSet n x ×ˢ s) / (ν a) (countablePartitionSet n x) ∂ν a =
    ∫⁻ (x : γ) in u, (κ a) (u ×ˢ s) / (ν a) u ∂ν a
h0 : (ν a) u = 0
h0' : (κ a) {p | p.1 ∈ u} = 0
⊢ u ×ˢ s ⊆ {p | p.1 ∈ u}

Proof state:
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
inst✝ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
hκν : κ.fst ≤ ν
hν : IsFiniteKernel ν
n : ℕ
a : α
s : Set β
hs : MeasurableSet s
u : Set γ
hu : u ∈ countablePartition γ n
this : IsFiniteKernel κ
hu_meas : MeasurableSet u
t : γ
ht : t ∈ u
⊢ (κ a) (countablePartitionSet n t ×ˢ s) / (ν a) (countablePartitionSet n t) = (κ a) (u ×ˢ s) / (ν a) u

Tactic:
rw [countablePartitionSet_of_mem hu ht]

Result:
no goals

Proof state:
case pos
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
inst✝ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
hκν : κ.fst ≤ ν
hν : IsFiniteKernel ν
n : ℕ
a : α
s : Set β
hs : MeasurableSet s
u : Set γ
hu : u ∈ countablePartition γ n
this : IsFiniteKernel κ
hu_meas : MeasurableSet u
x✝ : γ
h0 : (ν a) (countablePartitionSet n x✝) = 0
h0' : (κ a) {p | p.1 ∈ countablePartitionSet n x✝} = 0
x : γ × β
⊢ x.1 ∈ countablePartitionSet n x✝ → x.2 ∈ s → x.1 ∈ countablePartitionSet n x✝

Tactic:
exact fun h _ ↦ h

Result:
no goals

Proof state:
case pos
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
inst✝ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
hκν : κ.fst ≤ ν
hν : IsFiniteKernel ν
n : ℕ
a : α
s : Set β
hs : MeasurableSet s
u : Set γ
hu : u ∈ countablePartition γ n
this✝ : IsFiniteKernel κ
hu_meas : MeasurableSet u
this :
  ∫⁻ (x : γ) in u, (κ a) (countablePartitionSet n x ×ˢ s) / (ν a) (countablePartitionSet n x) ∂ν a =
    ∫⁻ (x : γ) in u, (κ a) (u ×ˢ s) / (ν a) u ∂ν a
h0 : (ν a) u = 0
h0' : (κ a) {p | p.1 ∈ u} = 0
p : γ × β
⊢ p ∈ u ×ˢ s → p ∈ {p | p.1 ∈ u}

Tactic:
simp only [mem_prod, mem_setOf_eq, and_imp]

Result:
case pos
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
inst✝ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
hκν : κ.fst ≤ ν
hν : IsFiniteKernel ν
n : ℕ
a : α
s : Set β
hs : MeasurableSet s
u : Set γ
hu : u ∈ countablePartition γ n
this✝ : IsFiniteKernel κ
hu_meas : MeasurableSet u
this :
  ∫⁻ (x : γ) in u, (κ a) (countablePartitionSet n x ×ˢ s) / (ν a) (countablePartitionSet n x) ∂ν a =
    ∫⁻ (x : γ) in u, (κ a) (u ×ˢ s) / (ν a) u ∂ν a
h0 : (ν a) u = 0
h0' : (κ a) {p | p.1 ∈ u} = 0
p : γ × β
⊢ p.1 ∈ u → p.2 ∈ s → p.1 ∈ u