Module: Mathlib.Probability.Kernel.IonescuTulcea.Traj

Goal state before:
pp: X : ℕ → Type u_1
inst✝¹ : (n : ℕ) → MeasurableSpace (X n)
κ : (n : ℕ) → Kernel ((i : ↥(Iic n)) → X ↑i) (X (n + 1))
inst✝ : ∀ (n : ℕ), IsMarkovKernel (κ n)
a b : ℕ
hab : a ≤ b
u : (i : ↥(Iic a)) → X ↑i
s : Set (((i : ↥(Iic b)) → X ↑i) × ((n : ℕ) → X n))
ms : MeasurableSet s
⊢ ∫⁻ (a : (i : ↥(Iic b)) → X ↑i), ((traj κ b) a) (Prod.mk a ⁻¹' s) ∂(partialTraj κ a b) u =
    ∫⁻ (b_1 : (i : ↥(Iic b)) → X ↑i), ((traj κ b) b_1) ((fun x ↦ (frestrictLe b x, x)) ⁻¹' s) ∂(partialTraj κ a b) u

pp: case hs
X : ℕ → Type u_1
inst✝¹ : (n : ℕ) → MeasurableSpace (X n)
κ : (n : ℕ) → Kernel ((i : ↥(Iic n)) → X ↑i) (X (n + 1))
inst✝ : ∀ (n : ℕ), IsMarkovKernel (κ n)
a b : ℕ
hab : a ≤ b
u : (i : ↥(Iic a)) → X ↑i
s : Set (((i : ↥(Iic b)) → X ↑i) × ((n : ℕ) → X n))
ms : MeasurableSet s
⊢ MeasurableSet ((fun x ↦ (frestrictLe b x, x)) ⁻¹' s)

pp: X : ℕ → Type u_1
inst✝¹ : (n : ℕ) → MeasurableSpace (X n)
κ : (n : ℕ) → Kernel ((i : ↥(Iic n)) → X ↑i) (X (n + 1))
inst✝ : ∀ (n : ℕ), IsMarkovKernel (κ n)
a b : ℕ
hab : a ≤ b
u : (i : ↥(Iic a)) → X ↑i
s : Set (((i : ↥(Iic b)) → X ↑i) × ((n : ℕ) → X n))
ms : MeasurableSet s
⊢ MeasurableSet s

pp: case hf
X : ℕ → Type u_1
inst✝¹ : (n : ℕ) → MeasurableSpace (X n)
κ : (n : ℕ) → Kernel ((i : ↥(Iic n)) → X ↑i) (X (n + 1))
inst✝ : ∀ (n : ℕ), IsMarkovKernel (κ n)
a b : ℕ
hab : a ≤ b
u : (i : ↥(Iic a)) → X ↑i
s : Set (((i : ↥(Iic b)) → X ↑i) × ((n : ℕ) → X n))
ms : MeasurableSet s
⊢ Measurable fun x ↦ (frestrictLe b x, x)

pp: case hs
X : ℕ → Type u_1
inst✝¹ : (n : ℕ) → MeasurableSpace (X n)
κ : (n : ℕ) → Kernel ((i : ↥(Iic n)) → X ↑i) (X (n + 1))
inst✝ : ∀ (n : ℕ), IsMarkovKernel (κ n)
a b : ℕ
hab : a ≤ b
u : (i : ↥(Iic a)) → X ↑i
s : Set (((i : ↥(Iic b)) → X ↑i) × ((n : ℕ) → X n))
ms : MeasurableSet s
⊢ MeasurableSet s

Tactic:
· congr 1 with x
    rw [← traj_map_updateFinset, Measure.map_apply, Measure.map_apply]
    · congr 1 with y
      simp only [Set.mem_preimage]
      congrm (fun i ↦ ?_, fun i ↦ ?_) ∈ s <;> simp [updateFinset]
    any_goals fun_prop
    all_goals exact ms.preimage (by fun_prop)

Goal state after:
case hs
X : ℕ → Type u_1
inst✝¹ : (n : ℕ) → MeasurableSpace (X n)
κ : (n : ℕ) → Kernel ((i : ↥(Iic n)) → X ↑i) (X (n + 1))
inst✝ : ∀ (n : ℕ), IsMarkovKernel (κ n)
a b : ℕ
hab : a ≤ b
u : (i : ↥(Iic a)) → X ↑i
s : Set (((i : ↥(Iic b)) → X ↑i) × ((n : ℕ) → X n))
ms : MeasurableSet s
⊢ MeasurableSet ((fun x ↦ (frestrictLe b x, x)) ⁻¹' s)

X : ℕ → Type u_1
inst✝¹ : (n : ℕ) → MeasurableSpace (X n)
κ : (n : ℕ) → Kernel ((i : ↥(Iic n)) → X ↑i) (X (n + 1))
inst✝ : ∀ (n : ℕ), IsMarkovKernel (κ n)
a b : ℕ
hab : a ≤ b
u : (i : ↥(Iic a)) → X ↑i
s : Set (((i : ↥(Iic b)) → X ↑i) × ((n : ℕ) → X n))
ms : MeasurableSet s
⊢ MeasurableSet s

case hf
X : ℕ → Type u_1
inst✝¹ : (n : ℕ) → MeasurableSpace (X n)
κ : (n : ℕ) → Kernel ((i : ↥(Iic n)) → X ↑i) (X (n + 1))
inst✝ : ∀ (n : ℕ), IsMarkovKernel (κ n)
a b : ℕ
hab : a ≤ b
u : (i : ↥(Iic a)) → X ↑i
s : Set (((i : ↥(Iic b)) → X ↑i) × ((n : ℕ) → X n))
ms : MeasurableSet s
⊢ Measurable fun x ↦ (frestrictLe b x, x)

case hs
X : ℕ → Type u_1
inst✝¹ : (n : ℕ) → MeasurableSpace (X n)
κ : (n : ℕ) → Kernel ((i : ↥(Iic n)) → X ↑i) (X (n + 1))
inst✝ : ∀ (n : ℕ), IsMarkovKernel (κ n)
a b : ℕ
hab : a ≤ b
u : (i : ↥(Iic a)) → X ↑i
s : Set (((i : ↥(Iic b)) → X ↑i) × ((n : ℕ) → X n))
ms : MeasurableSet s
⊢ MeasurableSet s