-- Mathlib/Probability/Kernel/Composition/CompProd.lean
lemma comapRight_compProd_id_prod {δ : Type*} {mδ : MeasurableSpace δ}
    (κ : Kernel α β) [IsSFiniteKernel κ] (η : Kernel (α × β) γ) [IsSFiniteKernel η]
    {f : δ → γ} (hf : MeasurableEmbedding f) :
    comapRight (κ ⊗ₖ η) (MeasurableEmbedding.id.prodMap hf) = κ ⊗ₖ (comapRight η hf)

Proof state:
case h.h.hs
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
δ : Type u_4
mδ : MeasurableSpace δ
κ : Kernel α β
inst✝¹ : IsSFiniteKernel κ
η : Kernel (α × β) γ
inst✝ : IsSFiniteKernel η
f : δ → γ
hf : MeasurableEmbedding f
a : α
t : Set (β × δ)
ht : MeasurableSet t
⊢ MeasurableSet (Prod.map id f '' t)

Tactic:
exact (MeasurableEmbedding.id.prodMap hf).measurableSet_image.mpr ht

Result:
no goals

Proof state:
case h.h.h.e_6.h.h
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
δ : Type u_4
mδ : MeasurableSpace δ
κ : Kernel α β
inst✝¹ : IsSFiniteKernel κ
η : Kernel (α × β) γ
inst✝ : IsSFiniteKernel η
f : δ → γ
hf : MeasurableEmbedding f
a : α
t : Set (β × δ)
ht : MeasurableSet t
b : β
x : γ
⊢ x ∈ {c | (b, c) ∈ Prod.map id f '' t} ↔ x ∈ f '' {c | (b, c) ∈ t}

Tactic:
aesop

Result:
no goals

Proof state:
case h.h.ht
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
δ : Type u_4
mδ : MeasurableSpace δ
κ : Kernel α β
inst✝¹ : IsSFiniteKernel κ
η : Kernel (α × β) γ
inst✝ : IsSFiniteKernel η
f : δ → γ
hf : MeasurableEmbedding f
a : α
t : Set (β × δ)
ht : MeasurableSet t
b : β
⊢ MeasurableSet {c | (b, c) ∈ t}

Tactic:
exact measurable_prod_mk_left ht

Result:
no goals

Proof state:
case h.h
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
δ : Type u_4
mδ : MeasurableSpace δ
κ : Kernel α β
inst✝¹ : IsSFiniteKernel κ
η : Kernel (α × β) γ
inst✝ : IsSFiniteKernel η
f : δ → γ
hf : MeasurableEmbedding f
a : α
t : Set (β × δ)
ht : MeasurableSet t
⊢ (((κ ⊗ₖ η).comapRight ⋯) a) t = ((κ ⊗ₖ η.comapRight hf) a) t

Tactic:
rw [comapRight_apply' _ _ _ ht, compProd_apply, compProd_apply ht]

Result:
case h.h
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
δ : Type u_4
mδ : MeasurableSpace δ
κ : Kernel α β
inst✝¹ : IsSFiniteKernel κ
η : Kernel (α × β) γ
inst✝ : IsSFiniteKernel η
f : δ → γ
hf : MeasurableEmbedding f
a : α
t : Set (β × δ)
ht : MeasurableSet t
⊢ ∫⁻ (b : β), (η (a, b)) {c | (b, c) ∈ Prod.map id f '' t} ∂κ a =
    ∫⁻ (b : β), ((η.comapRight hf) (a, b)) {c | (b, c) ∈ t} ∂κ a

case h.h.hs
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
δ : Type u_4
mδ : MeasurableSpace δ
κ : Kernel α β
inst✝¹ : IsSFiniteKernel κ
η : Kernel (α × β) γ
inst✝ : IsSFiniteKernel η
f : δ → γ
hf : MeasurableEmbedding f
a : α
t : Set (β × δ)
ht : MeasurableSet t
⊢ MeasurableSet (Prod.map id f '' t)

Proof state:
case h.h
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
δ : Type u_4
mδ : MeasurableSpace δ
κ : Kernel α β
inst✝¹ : IsSFiniteKernel κ
η : Kernel (α × β) γ
inst✝ : IsSFiniteKernel η
f : δ → γ
hf : MeasurableEmbedding f
a : α
t : Set (β × δ)
ht : MeasurableSet t
b : β
⊢ (η (a, b)) {c | (b, c) ∈ Prod.map id f '' t} = ((η.comapRight hf) (a, b)) {c | (b, c) ∈ t}

Tactic:
rw [comapRight_apply']

Result:
case h.h
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
δ : Type u_4
mδ : MeasurableSpace δ
κ : Kernel α β
inst✝¹ : IsSFiniteKernel κ
η : Kernel (α × β) γ
inst✝ : IsSFiniteKernel η
f : δ → γ
hf : MeasurableEmbedding f
a : α
t : Set (β × δ)
ht : MeasurableSet t
b : β
⊢ (η (a, b)) {c | (b, c) ∈ Prod.map id f '' t} = (η (a, b)) (f '' {c | (b, c) ∈ t})

case h.h.ht
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
δ : Type u_4
mδ : MeasurableSpace δ
κ : Kernel α β
inst✝¹ : IsSFiniteKernel κ
η : Kernel (α × β) γ
inst✝ : IsSFiniteKernel η
f : δ → γ
hf : MeasurableEmbedding f
a : α
t : Set (β × δ)
ht : MeasurableSet t
b : β
⊢ MeasurableSet {c | (b, c) ∈ t}

Proof state:
case h.h
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
δ : Type u_4
mδ : MeasurableSpace δ
κ : Kernel α β
inst✝¹ : IsSFiniteKernel κ
η : Kernel (α × β) γ
inst✝ : IsSFiniteKernel η
f : δ → γ
hf : MeasurableEmbedding f
a : α
t : Set (β × δ)
ht : MeasurableSet t
b : β
⊢ (η (a, b)) {c | (b, c) ∈ Prod.map id f '' t} = (η (a, b)) (f '' {c | (b, c) ∈ t})

Tactic:
congr with x

Result:
case h.h.h.e_6.h.h
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
δ : Type u_4
mδ : MeasurableSpace δ
κ : Kernel α β
inst✝¹ : IsSFiniteKernel κ
η : Kernel (α × β) γ
inst✝ : IsSFiniteKernel η
f : δ → γ
hf : MeasurableEmbedding f
a : α
t : Set (β × δ)
ht : MeasurableSet t
b : β
x : γ
⊢ x ∈ {c | (b, c) ∈ Prod.map id f '' t} ↔ x ∈ f '' {c | (b, c) ∈ t}

Proof state:
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
δ : Type u_4
mδ : MeasurableSpace δ
κ : Kernel α β
inst✝¹ : IsSFiniteKernel κ
η : Kernel (α × β) γ
inst✝ : IsSFiniteKernel η
f : δ → γ
hf : MeasurableEmbedding f
⊢ (κ ⊗ₖ η).comapRight ⋯ = κ ⊗ₖ η.comapRight hf

Tactic:
ext a t ht

Result:
case h.h
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
δ : Type u_4
mδ : MeasurableSpace δ
κ : Kernel α β
inst✝¹ : IsSFiniteKernel κ
η : Kernel (α × β) γ
inst✝ : IsSFiniteKernel η
f : δ → γ
hf : MeasurableEmbedding f
a : α
t : Set (β × δ)
ht : MeasurableSet t
⊢ (((κ ⊗ₖ η).comapRight ⋯) a) t = ((κ ⊗ₖ η.comapRight hf) a) t

Proof state:
case h.h
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
δ : Type u_4
mδ : MeasurableSpace δ
κ : Kernel α β
inst✝¹ : IsSFiniteKernel κ
η : Kernel (α × β) γ
inst✝ : IsSFiniteKernel η
f : δ → γ
hf : MeasurableEmbedding f
a : α
t : Set (β × δ)
ht : MeasurableSet t
⊢ ∫⁻ (b : β), (η (a, b)) {c | (b, c) ∈ Prod.map id f '' t} ∂κ a =
    ∫⁻ (b : β), ((η.comapRight hf) (a, b)) {c | (b, c) ∈ t} ∂κ a

Tactic:
refine lintegral_congr fun b ↦ ?_

Result:
case h.h
α : Type u_1
β : Type u_2
γ : Type u_3
mα : MeasurableSpace α
mβ : MeasurableSpace β
mγ : MeasurableSpace γ
δ : Type u_4
mδ : MeasurableSpace δ
κ : Kernel α β
inst✝¹ : IsSFiniteKernel κ
η : Kernel (α × β) γ
inst✝ : IsSFiniteKernel η
f : δ → γ
hf : MeasurableEmbedding f
a : α
t : Set (β × δ)
ht : MeasurableSet t
b : β
⊢ (η (a, b)) {c | (b, c) ∈ Prod.map id f '' t} = ((η.comapRight hf) (a, b)) {c | (b, c) ∈ t}