-- Mathlib/Probability/Kernel/Disintegration/Density.lean
lemma tendsto_densityProcess_atTop_empty_of_antitone (κ : Kernel α (γ × β)) (ν : Kernel α γ)
    [IsFiniteKernel κ] (n : ℕ) (a : α) (x : γ)
    (seq : ℕ → Set β) (hseq : Antitone seq) (hseq_iInter : ⋂ i, seq i = ∅)
    (hseq_meas : ∀ m, MeasurableSet (seq m)) :
    Tendsto (fun m ↦ densityProcess κ ν n a x (seq m)) atTop
      (𝓝 (densityProcess κ ν n a 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✝¹ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
inst✝ : IsFiniteKernel κ
n : ℕ
a : α
x : γ
seq : ℕ → Set β
hseq : Antitone seq
hseq_iInter : ⋂ i, seq i = ∅
hseq_meas : ∀ (m : ℕ), MeasurableSet (seq m)
h0 : ¬(ν a) (countablePartitionSet n x) = 0
⊢ Tendsto (fun m => ((κ a) (countablePartitionSet n x ×ˢ seq m) / (ν a) (countablePartitionSet n x)).toReal) atTop
    (𝓝 ((κ a) (countablePartitionSet n x ×ˢ ∅) / (ν a) (countablePartitionSet n x)).toReal)

Tactic:
refine (ENNReal.tendsto_toReal ?_).comp ?_

Result:
case neg.refine_1
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
inst✝¹ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
inst✝ : IsFiniteKernel κ
n : ℕ
a : α
x : γ
seq : ℕ → Set β
hseq : Antitone seq
hseq_iInter : ⋂ i, seq i = ∅
hseq_meas : ∀ (m : ℕ), MeasurableSet (seq m)
h0 : ¬(ν a) (countablePartitionSet n x) = 0
⊢ (κ a) (countablePartitionSet n x ×ˢ ∅) / (ν a) (countablePartitionSet n x) ≠ ⊤

case neg.refine_2
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
inst✝¹ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
inst✝ : IsFiniteKernel κ
n : ℕ
a : α
x : γ
seq : ℕ → Set β
hseq : Antitone seq
hseq_iInter : ⋂ i, seq i = ∅
hseq_meas : ∀ (m : ℕ), MeasurableSet (seq m)
h0 : ¬(ν a) (countablePartitionSet n x) = 0
⊢ Tendsto (fun m => (κ a) (countablePartitionSet n x ×ˢ seq m) / (ν a) (countablePartitionSet n x)) atTop
    (𝓝 ((κ a) (countablePartitionSet n x ×ˢ ∅) / (ν a) (countablePartitionSet n x)))

Proof state:
case hm
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
inst✝¹ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
inst✝ : IsFiniteKernel κ
n : ℕ
a : α
x : γ
seq : ℕ → Set β
hseq : Antitone seq
hseq_iInter : ⋂ i, seq i = ∅
hseq_meas : ∀ (m : ℕ), MeasurableSet (seq m)
h0 : ¬(ν a) (countablePartitionSet n x) = 0
⊢ Antitone fun m => countablePartitionSet n x ×ˢ seq m

Tactic:
exact fun _ _ h ↦ prod_mono_right <| hseq h

Result:
no goals

Proof state:
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
inst✝¹ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
inst✝ : IsFiniteKernel κ
n : ℕ
a : α
x : γ
seq : ℕ → Set β
hseq : Antitone seq
hseq_iInter : ⋂ i, seq i = ∅
hseq_meas : ∀ (m : ℕ), MeasurableSet (seq m)
⊢ Tendsto (fun m => ((κ a) (countablePartitionSet n x ×ˢ seq m) / (ν a) (countablePartitionSet n x)).toReal) atTop
    (𝓝 ((κ a) (countablePartitionSet n x ×ˢ ∅) / (ν a) (countablePartitionSet n x)).toReal)

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✝¹ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
inst✝ : IsFiniteKernel κ
n : ℕ
a : α
x : γ
seq : ℕ → Set β
hseq : Antitone seq
hseq_iInter : ⋂ i, seq i = ∅
hseq_meas : ∀ (m : ℕ), MeasurableSet (seq m)
h0 : (ν a) (countablePartitionSet n x) = 0
⊢ Tendsto (fun m => ((κ a) (countablePartitionSet n x ×ˢ seq m) / (ν a) (countablePartitionSet n x)).toReal) atTop
    (𝓝 ((κ a) (countablePartitionSet n x ×ˢ ∅) / (ν a) (countablePartitionSet n x)).toReal)

case neg
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
inst✝¹ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
inst✝ : IsFiniteKernel κ
n : ℕ
a : α
x : γ
seq : ℕ → Set β
hseq : Antitone seq
hseq_iInter : ⋂ i, seq i = ∅
hseq_meas : ∀ (m : ℕ), MeasurableSet (seq m)
h0 : ¬(ν a) (countablePartitionSet n x) = 0
⊢ Tendsto (fun m => ((κ a) (countablePartitionSet n x ×ˢ seq m) / (ν a) (countablePartitionSet n x)).toReal) atTop
    (𝓝 ((κ a) (countablePartitionSet n x ×ˢ ∅) / (ν a) (countablePartitionSet n x)).toReal)

Proof state:
case neg.refine_2
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
inst✝¹ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
inst✝ : IsFiniteKernel κ
n : ℕ
a : α
x : γ
seq : ℕ → Set β
hseq : Antitone seq
hseq_iInter : ⋂ i, seq i = ∅
hseq_meas : ∀ (m : ℕ), MeasurableSet (seq m)
h0 : ¬(ν a) (countablePartitionSet n x) = 0
this :
  Tendsto (fun m => (κ a) (countablePartitionSet n x ×ˢ seq m)) atTop
    (𝓝 ((κ a) (⋂ n_1, countablePartitionSet n x ×ˢ seq n_1)))
⊢ Tendsto (fun m => (κ a) (countablePartitionSet n x ×ˢ seq m)) atTop (𝓝 ((κ a) (countablePartitionSet n x ×ˢ ∅)))

Tactic:
simpa only [← prod_iInter, hseq_iInter] using this

Result:
no goals

Proof state:
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
inst✝¹ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
inst✝ : IsFiniteKernel κ
n : ℕ
a : α
x : γ
seq : ℕ → Set β
hseq : Antitone seq
hseq_iInter : ⋂ i, seq i = ∅
hseq_meas : ∀ (m : ℕ), MeasurableSet (seq m)
h0 : ¬(ν a) (countablePartitionSet n x) = 0
⊢ Tendsto (fun m => (κ a) (countablePartitionSet n x ×ˢ seq m)) atTop
    (𝓝 ((κ a) (⋂ n_1, countablePartitionSet n x ×ˢ seq n_1)))

Tactic:
apply tendsto_measure_iInter_atTop

Result:
case hs
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
inst✝¹ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
inst✝ : IsFiniteKernel κ
n : ℕ
a : α
x : γ
seq : ℕ → Set β
hseq : Antitone seq
hseq_iInter : ⋂ i, seq i = ∅
hseq_meas : ∀ (m : ℕ), MeasurableSet (seq m)
h0 : ¬(ν a) (countablePartitionSet n x) = 0
⊢ ∀ (i : ℕ), NullMeasurableSet (countablePartitionSet n x ×ˢ seq i) (κ a)

case hm
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
inst✝¹ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
inst✝ : IsFiniteKernel κ
n : ℕ
a : α
x : γ
seq : ℕ → Set β
hseq : Antitone seq
hseq_iInter : ⋂ i, seq i = ∅
hseq_meas : ∀ (m : ℕ), MeasurableSet (seq m)
h0 : ¬(ν a) (countablePartitionSet n x) = 0
⊢ Antitone fun m => countablePartitionSet n x ×ˢ seq m

case hf
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
inst✝¹ : CountablyGenerated γ
κ : Kernel α (γ × β)
ν : Kernel α γ
inst✝ : IsFiniteKernel κ
n : ℕ
a : α
x : γ
seq : ℕ → Set β
hseq : Antitone seq
hseq_iInter : ⋂ i, seq i = ∅
hseq_meas : ∀ (m : ℕ), MeasurableSet (seq m)
h0 : ¬(ν a) (countablePartitionSet n x) = 0
⊢ ∃ i, (κ a) (countablePartitionSet n x ×ˢ seq i) ≠ ⊤