Theorem: ProbabilityTheory.Kernel.measurable_kernel_prod_mk_left
File: Mathlib/Probability/Kernel/MeasurableIntegral.lean

Proof steps:
state_before: α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
κ : Kernel α β
η : Kernel (α × β) γ
a : α
inst✝ : IsSFiniteKernel κ
t : Set (α × β)
ht : MeasurableSet t
⊢ Measurable fun a => (κ a) (Prod.mk a ⁻¹' t)
state_after: α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
κ : Kernel α β
η : Kernel (α × β) γ
a : α
inst✝ : IsSFiniteKernel κ
t : Set (α × β)
ht : MeasurableSet t
⊢ Measurable fun a => ((Kernel.sum κ.seq) a) (Prod.mk a ⁻¹' t)
tactic: rw [← Kernel.kernel_sum_seq κ]
state_before: α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
κ : Kernel α β
η : Kernel (α × β) γ
a : α
inst✝ : IsSFiniteKernel κ
t : Set (α × β)
ht : MeasurableSet t
⊢ Measurable fun a => ((Kernel.sum κ.seq) a) (Prod.mk a ⁻¹' t)
state_after: α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
κ : Kernel α β
η : Kernel (α × β) γ
a : α
inst✝ : IsSFiniteKernel κ
t : Set (α × β)
ht : MeasurableSet t
this : ∀ (a : α), ((Kernel.sum κ.seq) a) (Prod.mk a ⁻¹' t) = ∑' (n : ℕ), ((κ.seq n) a) (Prod.mk a ⁻¹' t)
⊢ Measurable fun a => ((Kernel.sum κ.seq) a) (Prod.mk a ⁻¹' t)
tactic: have : ∀ a, Kernel.sum (Kernel.seq κ) a (Prod.mk a ⁻¹' t) =
      ∑' n, Kernel.seq κ n a (Prod.mk a ⁻¹' t) := fun a =>
    Kernel.sum_apply' _ _ (measurable_prod_mk_left ht)
state_before: α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
κ : Kernel α β
η : Kernel (α × β) γ
a : α
inst✝ : IsSFiniteKernel κ
t : Set (α × β)
ht : MeasurableSet t
this : ∀ (a : α), ((Kernel.sum κ.seq) a) (Prod.mk a ⁻¹' t) = ∑' (n : ℕ), ((κ.seq n) a) (Prod.mk a ⁻¹' t)
⊢ Measurable fun a => ((Kernel.sum κ.seq) a) (Prod.mk a ⁻¹' t)
state_after: α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
κ : Kernel α β
η : Kernel (α × β) γ
a : α
inst✝ : IsSFiniteKernel κ
t : Set (α × β)
ht : MeasurableSet t
this : ∀ (a : α), ((Kernel.sum κ.seq) a) (Prod.mk a ⁻¹' t) = ∑' (n : ℕ), ((κ.seq n) a) (Prod.mk a ⁻¹' t)
⊢ Measurable fun a => ∑' (n : ℕ), ((κ.seq n) a) (Prod.mk a ⁻¹' t)
tactic: simp_rw [this]
state_before: α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
κ : Kernel α β
η : Kernel (α × β) γ
a : α
inst✝ : IsSFiniteKernel κ
t : Set (α × β)
ht : MeasurableSet t
this : ∀ (a : α), ((Kernel.sum κ.seq) a) (Prod.mk a ⁻¹' t) = ∑' (n : ℕ), ((κ.seq n) a) (Prod.mk a ⁻¹' t)
⊢ Measurable fun a => ∑' (n : ℕ), ((κ.seq n) a) (Prod.mk a ⁻¹' t)
state_after: α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
κ : Kernel α β
η : Kernel (α × β) γ
a : α
inst✝ : IsSFiniteKernel κ
t : Set (α × β)
ht : MeasurableSet t
this : ∀ (a : α), ((Kernel.sum κ.seq) a) (Prod.mk a ⁻¹' t) = ∑' (n : ℕ), ((κ.seq n) a) (Prod.mk a ⁻¹' t)
n : ℕ
⊢ Measurable fun a => ((κ.seq n) a) (Prod.mk a ⁻¹' t)
tactic: refine Measurable.ennreal_tsum fun n => ?_
state_before: α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
κ : Kernel α β
η : Kernel (α × β) γ
a : α
inst✝ : IsSFiniteKernel κ
t : Set (α × β)
ht : MeasurableSet t
this : ∀ (a : α), ((Kernel.sum κ.seq) a) (Prod.mk a ⁻¹' t) = ∑' (n : ℕ), ((κ.seq n) a) (Prod.mk a ⁻¹' t)
n : ℕ
⊢ Measurable fun a => ((κ.seq n) a) (Prod.mk a ⁻¹' t)
state_after: no goals
tactic: exact measurable_kernel_prod_mk_left_of_finite ht inferInstance