Module: Mathlib.Probability.ProductMeasure

Goal state before:
pp: case inl.refine_2
X : ℕ → Type u_1
mX : (n : ℕ) → MeasurableSpace (X n)
μ : (n : ℕ) → Measure (X n)
hμ : ∀ (n : ℕ), IsProbabilityMeasure (μ n)
a b : ℕ
hab : a < b
n : ℕ
hn : a.succ ≤ n
hind :
  (partialTraj (fun n ↦ const ((i : ↥(Iic n)) → X ↑i) (μ (n + 1))) a n).map (restrict₂ ⋯) =
    const ((i : ↥(Iic a)) → X ↑i) (Measure.pi fun i ↦ μ ↑i)
x₀ : (i : ↥(Iic a)) → X ↑i
this : restrict₂ ⋯ ∘ _root_.IicProdIoc n (n + 1) = IocProdIoc a n (n + 1) ∘ Prod.map (restrict₂ ⋯) id
⊢ (((partialTraj (fun n ↦ const ((i : ↥(Iic n)) → X ↑i) (μ (n + 1))) a n ×ₖ
                const ((i : ↥(Iic a)) → X ↑i) (Measure.map (⇑(piSingleton n)) (μ (n + 1)))).map
            (_root_.IicProdIoc n (n + 1))).map
        (restrict₂ ⋯))
      x₀ =
    Measure.pi fun i ↦ μ ↑i

pp: case inl.refine_2.hf
X : ℕ → Type u_1
mX : (n : ℕ) → MeasurableSpace (X n)
μ : (n : ℕ) → Measure (X n)
hμ : ∀ (n : ℕ), IsProbabilityMeasure (μ n)
a b : ℕ
hab : a < b
n : ℕ
hn : a.succ ≤ n
hind :
  (partialTraj (fun n ↦ const ((i : ↥(Iic n)) → X ↑i) (μ (n + 1))) a n).map (restrict₂ ⋯) =
    const ((i : ↥(Iic a)) → X ↑i) (Measure.pi fun i ↦ μ ↑i)
x₀ : (i : ↥(Iic a)) → X ↑i
this : restrict₂ ⋯ ∘ _root_.IicProdIoc n (n + 1) = IocProdIoc a n (n + 1) ∘ Prod.map (restrict₂ ⋯) id
⊢ Measurable ⇑(piSingleton n)

Tactic:
← map_comp_right,

Goal state after:
case inl.refine_2
X : ℕ → Type u_1
mX : (n : ℕ) → MeasurableSpace (X n)
μ : (n : ℕ) → Measure (X n)
hμ : ∀ (n : ℕ), IsProbabilityMeasure (μ n)
a b : ℕ
hab : a < b
n : ℕ
hn : a.succ ≤ n
hind :
  (partialTraj (fun n ↦ const ((i : ↥(Iic n)) → X ↑i) (μ (n + 1))) a n).map (restrict₂ ⋯) =
    const ((i : ↥(Iic a)) → X ↑i) (Measure.pi fun i ↦ μ ↑i)
x₀ : (i : ↥(Iic a)) → X ↑i
this : restrict₂ ⋯ ∘ _root_.IicProdIoc n (n + 1) = IocProdIoc a n (n + 1) ∘ Prod.map (restrict₂ ⋯) id
⊢ ((partialTraj (fun n ↦ const ((i : ↥(Iic n)) → X ↑i) (μ (n + 1))) a n ×ₖ
            const ((i : ↥(Iic a)) → X ↑i) (Measure.map (⇑(piSingleton n)) (μ (n + 1)))).map
        (restrict₂ ⋯ ∘ _root_.IicProdIoc n (n + 1)))
      x₀ =
    Measure.pi fun i ↦ μ ↑i

case inl.refine_2.hf
X : ℕ → Type u_1
mX : (n : ℕ) → MeasurableSpace (X n)
μ : (n : ℕ) → Measure (X n)
hμ : ∀ (n : ℕ), IsProbabilityMeasure (μ n)
a b : ℕ
hab : a < b
n : ℕ
hn : a.succ ≤ n
hind :
  (partialTraj (fun n ↦ const ((i : ↥(Iic n)) → X ↑i) (μ (n + 1))) a n).map (restrict₂ ⋯) =
    const ((i : ↥(Iic a)) → X ↑i) (Measure.pi fun i ↦ μ ↑i)
x₀ : (i : ↥(Iic a)) → X ↑i
this : restrict₂ ⋯ ∘ _root_.IicProdIoc n (n + 1) = IocProdIoc a n (n + 1) ∘ Prod.map (restrict₂ ⋯) id
⊢ Measurable (_root_.IicProdIoc n (n + 1))

case inl.refine_2.hg
X : ℕ → Type u_1
mX : (n : ℕ) → MeasurableSpace (X n)
μ : (n : ℕ) → Measure (X n)
hμ : ∀ (n : ℕ), IsProbabilityMeasure (μ n)
a b : ℕ
hab : a < b
n : ℕ
hn : a.succ ≤ n
hind :
  (partialTraj (fun n ↦ const ((i : ↥(Iic n)) → X ↑i) (μ (n + 1))) a n).map (restrict₂ ⋯) =
    const ((i : ↥(Iic a)) → X ↑i) (Measure.pi fun i ↦ μ ↑i)
x₀ : (i : ↥(Iic a)) → X ↑i
this : restrict₂ ⋯ ∘ _root_.IicProdIoc n (n + 1) = IocProdIoc a n (n + 1) ∘ Prod.map (restrict₂ ⋯) id
⊢ Measurable (restrict₂ ⋯)

case inl.refine_2.hf
X : ℕ → Type u_1
mX : (n : ℕ) → MeasurableSpace (X n)
μ : (n : ℕ) → Measure (X n)
hμ : ∀ (n : ℕ), IsProbabilityMeasure (μ n)
a b : ℕ
hab : a < b
n : ℕ
hn : a.succ ≤ n
hind :
  (partialTraj (fun n ↦ const ((i : ↥(Iic n)) → X ↑i) (μ (n + 1))) a n).map (restrict₂ ⋯) =
    const ((i : ↥(Iic a)) → X ↑i) (Measure.pi fun i ↦ μ ↑i)
x₀ : (i : ↥(Iic a)) → X ↑i
this : restrict₂ ⋯ ∘ _root_.IicProdIoc n (n + 1) = IocProdIoc a n (n + 1) ∘ Prod.map (restrict₂ ⋯) id
⊢ Measurable ⇑(piSingleton n)