-- Mathlib/Topology/Category/Profinite/Nobeling.lean
theorem CC_exact {f : LocallyConstant C ℤ} (hf : Linear_CC' C hsC ho f = 0) :
    ∃ y, πs C o y = f

Proof state:
case refine_3.h.mk
I : Type u
C : Set (I → Bool)
inst✝¹ : LinearOrder I
inst✝ : WellFoundedLT I
o : Ordinal.{u}
hC : IsClosed C
hsC : contained C (Order.succ o)
ho : o < Ordinal.type fun x1 x2 => x1 < x2
f : LocallyConstant ↑C ℤ
hf :
  ⇑((LocallyConstant.comapₗ ℤ { toFun := CC'₁ C hsC ho, continuous_toFun := ⋯ }) f) =
    ⇑((LocallyConstant.comapₗ ℤ { toFun := CC'₀ C ho, continuous_toFun := ⋯ }) f)
C₀C : ↑(C0 C ho) → ↑C := fun x => ⟨↑x, ⋯⟩
h₀ : Continuous C₀C
C₁C : ↑(π (C1 C ho) fun x => ord I x < o) → ↑C := fun x => ⟨SwapTrue o ↑x, ⋯⟩
h₁ : Continuous C₁C
x : I → Bool
hx : x ∈ C
⊢ ((πs C o)
        (LocallyConstant.piecewise' ⋯ ⋯ ⋯ (LocallyConstant.comap { toFun := C₀C, continuous_toFun := h₀ } f)
          (LocallyConstant.comap { toFun := C₁C, continuous_toFun := h₁ } f) ⋯))
      ⟨x, hx⟩ =
    f ⟨x, hx⟩

Tactic:
rw [← union_C0C1_eq C ho] at hx

Result:
case refine_3.h.mk
I : Type u
C : Set (I → Bool)
inst✝¹ : LinearOrder I
inst✝ : WellFoundedLT I
o : Ordinal.{u}
hC : IsClosed C
hsC : contained C (Order.succ o)
ho : o < Ordinal.type fun x1 x2 => x1 < x2
f : LocallyConstant ↑C ℤ
hf :
  ⇑((LocallyConstant.comapₗ ℤ { toFun := CC'₁ C hsC ho, continuous_toFun := ⋯ }) f) =
    ⇑((LocallyConstant.comapₗ ℤ { toFun := CC'₀ C ho, continuous_toFun := ⋯ }) f)
C₀C : ↑(C0 C ho) → ↑C := fun x => ⟨↑x, ⋯⟩
h₀ : Continuous C₀C
C₁C : ↑(π (C1 C ho) fun x => ord I x < o) → ↑C := fun x => ⟨SwapTrue o ↑x, ⋯⟩
h₁ : Continuous C₁C
x : I → Bool
hx✝ : x ∈ C
hx : x ∈ C0 C ho ∪ C1 C ho
⊢ ((πs C o)
        (LocallyConstant.piecewise' ⋯ ⋯ ⋯ (LocallyConstant.comap { toFun := C₀C, continuous_toFun := h₀ } f)
          (LocallyConstant.comap { toFun := C₁C, continuous_toFun := h₁ } f) ⋯))
      ⟨x, hx✝⟩ =
    f ⟨x, hx✝⟩

Proof state:
case refine_2
I : Type u
C : Set (I → Bool)
inst✝¹ : LinearOrder I
inst✝ : WellFoundedLT I
o : Ordinal.{u}
hC : IsClosed C
hsC : contained C (Order.succ o)
ho : o < Ordinal.type fun x1 x2 => x1 < x2
f : LocallyConstant ↑C ℤ
hf :
  ⇑((LocallyConstant.comapₗ ℤ { toFun := CC'₁ C hsC ho, continuous_toFun := ⋯ }) f) =
    ⇑((LocallyConstant.comapₗ ℤ { toFun := CC'₀ C ho, continuous_toFun := ⋯ }) f)
C₀C : ↑(C0 C ho) → ↑C := fun x => ⟨↑x, ⋯⟩
h₀ : Continuous C₀C
C₁C : ↑(π (C1 C ho) fun x => ord I x < o) → ↑C := fun x => ⟨SwapTrue o ↑x, ⋯⟩
h₁ : Continuous C₁C
x : I → Bool
hx : x ∈ C0 C ho ∩ π (C1 C ho) fun x => ord I x < o
⊢ (LocallyConstant.comap { toFun := C₀C, continuous_toFun := h₀ } f) ⟨x, ⋯⟩ =
    (LocallyConstant.comap { toFun := C₁C, continuous_toFun := h₁ } f) ⟨x, ⋯⟩

Tactic:
simpa only [h₀, h₁, LocallyConstant.coe_comap] using (congrFun hf ⟨x, hx⟩).symm

Result:
no goals

Proof state:
I : Type u
C : Set (I → Bool)
inst✝¹ : LinearOrder I
inst✝ : WellFoundedLT I
o : Ordinal.{u}
hC : IsClosed C
hsC : contained C (Order.succ o)
ho : o < Ordinal.type fun x1 x2 => x1 < x2
f : LocallyConstant ↑C ℤ
hf : (Linear_CC' C hsC ho) f = 0
⊢ ∃ y, (πs C o) y = f

Tactic:
dsimp [Linear_CC', Linear_CC'₀, Linear_CC'₁] at hf

Result:
I : Type u
C : Set (I → Bool)
inst✝¹ : LinearOrder I
inst✝ : WellFoundedLT I
o : Ordinal.{u}
hC : IsClosed C
hsC : contained C (Order.succ o)
ho : o < Ordinal.type fun x1 x2 => x1 < x2
f : LocallyConstant ↑C ℤ
hf :
  (LocallyConstant.comapₗ ℤ { toFun := CC'₁ C hsC ho, continuous_toFun := ⋯ }) f -
      (LocallyConstant.comapₗ ℤ { toFun := CC'₀ C ho, continuous_toFun := ⋯ }) f =
    0
⊢ ∃ y, (πs C o) y = f

Proof state:
I : Type u
C : Set (I → Bool)
inst✝¹ : LinearOrder I
inst✝ : WellFoundedLT I
o : Ordinal.{u}
hC : IsClosed C
hsC : contained C (Order.succ o)
ho : o < Ordinal.type fun x1 x2 => x1 < x2
f : LocallyConstant ↑C ℤ
hf :
  ⇑((LocallyConstant.comapₗ ℤ { toFun := CC'₁ C hsC ho, continuous_toFun := ⋯ }) f) =
    ⇑((LocallyConstant.comapₗ ℤ { toFun := CC'₀ C ho, continuous_toFun := ⋯ }) f)
C₀C : ↑(C0 C ho) → ↑C := fun x => ⟨↑x, ⋯⟩
h₀ : Continuous C₀C
C₁C : ↑(π (C1 C ho) fun x => ord I x < o) → ↑C := fun x => ⟨SwapTrue o ↑x, ⋯⟩
h₁ : Continuous C₁C
⊢ ∃ y, (πs C o) y = f

Tactic:
refine ⟨LocallyConstant.piecewise' ?_ (isClosed_C0 C hC ho)
    (isClosed_proj _ o (isClosed_C1 C hC ho)) (f.comap ⟨C₀C, h₀⟩) (f.comap ⟨C₁C, h₁⟩) ?_, ?_⟩

Result:
case refine_1
I : Type u
C : Set (I → Bool)
inst✝¹ : LinearOrder I
inst✝ : WellFoundedLT I
o : Ordinal.{u}
hC : IsClosed C
hsC : contained C (Order.succ o)
ho : o < Ordinal.type fun x1 x2 => x1 < x2
f : LocallyConstant ↑C ℤ
hf :
  ⇑((LocallyConstant.comapₗ ℤ { toFun := CC'₁ C hsC ho, continuous_toFun := ⋯ }) f) =
    ⇑((LocallyConstant.comapₗ ℤ { toFun := CC'₀ C ho, continuous_toFun := ⋯ }) f)
C₀C : ↑(C0 C ho) → ↑C := fun x => ⟨↑x, ⋯⟩
h₀ : Continuous C₀C
C₁C : ↑(π (C1 C ho) fun x => ord I x < o) → ↑C := fun x => ⟨SwapTrue o ↑x, ⋯⟩
h₁ : Continuous C₁C
⊢ (π C fun x => ord I x < o) ⊆ C0 C ho ∪ π (C1 C ho) fun x => ord I x < o

case refine_2
I : Type u
C : Set (I → Bool)
inst✝¹ : LinearOrder I
inst✝ : WellFoundedLT I
o : Ordinal.{u}
hC : IsClosed C
hsC : contained C (Order.succ o)
ho : o < Ordinal.type fun x1 x2 => x1 < x2
f : LocallyConstant ↑C ℤ
hf :
  ⇑((LocallyConstant.comapₗ ℤ { toFun := CC'₁ C hsC ho, continuous_toFun := ⋯ }) f) =
    ⇑((LocallyConstant.comapₗ ℤ { toFun := CC'₀ C ho, continuous_toFun := ⋯ }) f)
C₀C : ↑(C0 C ho) → ↑C := fun x => ⟨↑x, ⋯⟩
h₀ : Continuous C₀C
C₁C : ↑(π (C1 C ho) fun x => ord I x < o) → ↑C := fun x => ⟨SwapTrue o ↑x, ⋯⟩
h₁ : Continuous C₁C
⊢ ∀ (x : I → Bool) (hx : x ∈ C0 C ho ∩ π (C1 C ho) fun x => ord I x < o),
    (LocallyConstant.comap { toFun := C₀C, continuous_toFun := h₀ } f) ⟨x, ⋯⟩ =
      (LocallyConstant.comap { toFun := C₁C, continuous_toFun := h₁ } f) ⟨x, ⋯⟩

case refine_3
I : Type u
C : Set (I → Bool)
inst✝¹ : LinearOrder I
inst✝ : WellFoundedLT I
o : Ordinal.{u}
hC : IsClosed C
hsC : contained C (Order.succ o)
ho : o < Ordinal.type fun x1 x2 => x1 < x2
f : LocallyConstant ↑C ℤ
hf :
  ⇑((LocallyConstant.comapₗ ℤ { toFun := CC'₁ C hsC ho, continuous_toFun := ⋯ }) f) =
    ⇑((LocallyConstant.comapₗ ℤ { toFun := CC'₀ C ho, continuous_toFun := ⋯ }) f)
C₀C : ↑(C0 C ho) → ↑C := fun x => ⟨↑x, ⋯⟩
h₀ : Continuous C₀C
C₁C : ↑(π (C1 C ho) fun x => ord I x < o) → ↑C := fun x => ⟨SwapTrue o ↑x, ⋯⟩
h₁ : Continuous C₁C
⊢ (πs C o)
      (LocallyConstant.piecewise' ?refine_1 ⋯ ⋯ (LocallyConstant.comap { toFun := C₀C, continuous_toFun := h₀ } f)
        (LocallyConstant.comap { toFun := C₁C, continuous_toFun := h₁ } f) ?refine_2) =
    f

Proof state:
case refine_1.intro.intro
I : Type u
C : Set (I → Bool)
inst✝¹ : LinearOrder I
inst✝ : WellFoundedLT I
o : Ordinal.{u}
hC : IsClosed C
hsC : contained C (Order.succ o)
ho : o < Ordinal.type fun x1 x2 => x1 < x2
f : LocallyConstant ↑C ℤ
hf :
  ⇑((LocallyConstant.comapₗ ℤ { toFun := CC'₁ C hsC ho, continuous_toFun := ⋯ }) f) =
    ⇑((LocallyConstant.comapₗ ℤ { toFun := CC'₀ C ho, continuous_toFun := ⋯ }) f)
C₀C : ↑(C0 C ho) → ↑C := fun x => ⟨↑x, ⋯⟩
h₀ : Continuous C₀C
C₁C : ↑(π (C1 C ho) fun x => ord I x < o) → ↑C := fun x => ⟨SwapTrue o ↑x, ⋯⟩
h₁ : Continuous C₁C
y : I → Bool
hyC : y ∈ C
⊢ Proj (fun x => ord I x < o) y ∈ C0 C ho ∨ Proj (fun x => ord I x < o) y ∈ π (C1 C ho) fun x => ord I x < o

Tactic:
rw [← union_C0C1_eq C ho] at hyC

Result:
case refine_1.intro.intro
I : Type u
C : Set (I → Bool)
inst✝¹ : LinearOrder I
inst✝ : WellFoundedLT I
o : Ordinal.{u}
hC : IsClosed C
hsC : contained C (Order.succ o)
ho : o < Ordinal.type fun x1 x2 => x1 < x2
f : LocallyConstant ↑C ℤ
hf :
  ⇑((LocallyConstant.comapₗ ℤ { toFun := CC'₁ C hsC ho, continuous_toFun := ⋯ }) f) =
    ⇑((LocallyConstant.comapₗ ℤ { toFun := CC'₀ C ho, continuous_toFun := ⋯ }) f)
C₀C : ↑(C0 C ho) → ↑C := fun x => ⟨↑x, ⋯⟩
h₀ : Continuous C₀C
C₁C : ↑(π (C1 C ho) fun x => ord I x < o) → ↑C := fun x => ⟨SwapTrue o ↑x, ⋯⟩
h₁ : Continuous C₁C
y : I → Bool
hyC : y ∈ C0 C ho ∪ C1 C ho
⊢ Proj (fun x => ord I x < o) y ∈ C0 C ho ∨ Proj (fun x => ord I x < o) y ∈ π (C1 C ho) fun x => ord I x < o