-- Module: Mathlib.Condensed.Light.EffectiveEpi
Goal:
X Y : LightProfinite
f : X ⟶ Y
hf : Epi f
S : LightProfinite
g :
  (lightProfiniteToLightCondSet.obj Y).obj (P := Presheaf.IsSheaf (coherentTopology LightProfinite)).obj (Opposite.op S)
y :
  (fun
        (X :
          CompHausLike fun (X : TopCat.{u_1}) ↦
            TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1)) ↦
      (↑(X.toTop (P := fun (X : TopCat.{u_1}) ↦
            TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1))) :
        Type u_1))
    S
rw :
  ∀
    (hf :
      Function.Surjective (α :=
        (fun
              (X :
                CompHausLike fun (X : TopCat.{u_1}) ↦
                  TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1)) ↦
            (↑(X.toTop (P := fun (X : TopCat.{u_1}) ↦
                  TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1))) :
              Type u_1))
          X)
        (β :=
        (fun
              (X :
                CompHausLike fun (X : TopCat.{u_1}) ↦
                  TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1)) ↦
            (↑(X.toTop (P := fun (X : TopCat.{u_1}) ↦
                  TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1))) :
              Type u_1))
          Y)
        (⇑(ConcreteCategory.hom (FC :=
              fun
                (x1 x2 :
                  CompHausLike fun (X : TopCat.{u_1}) ↦
                    TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1)) ↦
              C((↑(x1.toTop (P := fun (X : TopCat.{u_1}) ↦
                      TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1))) :
                  Type u_1),
                (↑(x2.toTop (P := fun (X : TopCat.{u_1}) ↦
                      TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1))) :
                  Type u_1)))
              (CC :=
              fun
                (X :
                  CompHausLike fun (X : TopCat.{u_1}) ↦
                    TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1)) ↦
              (↑(X.toTop (P := fun (X : TopCat.{u_1}) ↦
                    TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1))) :
                Type u_1))
              f) :
          (a :
              (fun
                    (X :
                      CompHausLike fun (X : TopCat) ↦
                        TotallyDisconnectedSpace (↑X : Type u_1) ∧ SecondCountableTopology (↑X : Type u_1)) ↦
                  (↑X.toTop : Type u_1))
                X) →
            (fun
                  (X :
                    CompHausLike fun (X : TopCat) ↦
                      TotallyDisconnectedSpace (↑X : Type u_1) ∧ SecondCountableTopology (↑X : Type u_1)) ↦
                (↑X.toTop : Type u_1))
              Y))
    (S : LightProfinite.{u_1})
    (g :
      (lightProfiniteToLightCondSet.obj Y).obj (P := Presheaf.IsSheaf (coherentTopology LightProfinite)).obj
        (Opposite.op S))
    (y :
      (↑(S.toTop (P := fun (X : TopCat.{u_1}) ↦
            TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1))) :
        Type u_1)),
    ∃ (a :
      (fun
            (X :
              CompHausLike fun (X : TopCat.{u_1}) ↦
                TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1)) ↦
          (↑(X.toTop (P := fun (X : TopCat.{u_1}) ↦
                TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1))) :
            Type u_1))
        (pullback (P := fun (X : TopCat.{u_1}) ↦
          TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1)) f g)),
      (ConcreteCategory.hom (FC :=
              fun
                (x1 x2 :
                  CompHausLike fun (X : TopCat.{u_1}) ↦
                    TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1)) ↦
              C((↑(x1.toTop (P := fun (X : TopCat.{u_1}) ↦
                      TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1))) :
                  Type u_1),
                (↑(x2.toTop (P := fun (X : TopCat.{u_1}) ↦
                      TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1))) :
                  Type u_1)))
              (CC :=
              fun
                (X :
                  CompHausLike fun (X : TopCat.{u_1}) ↦
                    TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1)) ↦
              (↑(X.toTop (P := fun (X : TopCat.{u_1}) ↦
                    TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1))) :
                Type u_1))
              (X :=
              pullback (P := fun (X : TopCat.{u_1}) ↦
                TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1)) f g)
              (pullback.snd (P := fun (X : TopCat.{u_1}) ↦
                TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1)) f g) :
            (a :
                (fun
                      (X :
                        CompHausLike fun (X : TopCat) ↦
                          TotallyDisconnectedSpace (↑X : Type u_1) ∧ SecondCountableTopology (↑X : Type u_1)) ↦
                    (↑X.toTop : Type u_1))
                  (pullback f g)) →
              (fun
                    (X :
                      CompHausLike fun (X : TopCat) ↦
                        TotallyDisconnectedSpace (↑X : Type u_1) ∧ SecondCountableTopology (↑X : Type u_1)) ↦
                  (↑X.toTop : Type u_1))
                S)
          a =
        y
⊢ ∃ (a :
    (fun
          (X :
            CompHausLike fun (X : TopCat.{u_1}) ↦
              TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1)) ↦
        (↑(X.toTop (P := fun (X : TopCat.{u_1}) ↦
              TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1))) :
          Type u_1))
      (pullback (P := fun (X : TopCat.{u_1}) ↦
        TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1)) f g)),
    (ConcreteCategory.hom (FC :=
            fun
              (x1 x2 :
                CompHausLike fun (X : TopCat.{u_1}) ↦
                  TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1)) ↦
            C((↑(x1.toTop (P := fun (X : TopCat.{u_1}) ↦
                    TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1))) :
                Type u_1),
              (↑(x2.toTop (P := fun (X : TopCat.{u_1}) ↦
                    TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1))) :
                Type u_1)))
            (CC :=
            fun
              (X :
                CompHausLike fun (X : TopCat.{u_1}) ↦
                  TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1)) ↦
            (↑(X.toTop (P := fun (X : TopCat.{u_1}) ↦
                  TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1))) :
              Type u_1))
            (X :=
            pullback (P := fun (X : TopCat.{u_1}) ↦
              TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1)) f g)
            (pullback.snd (P := fun (X : TopCat.{u_1}) ↦
              TotallyDisconnectedSpace.{u_1} (↑X : Type u_1) ∧ SecondCountableTopology.{u_1} (↑X : Type u_1)) f g) :
          (a :
              (fun
                    (X :
                      CompHausLike fun (X : TopCat) ↦
                        TotallyDisconnectedSpace (↑X : Type u_1) ∧ SecondCountableTopology (↑X : Type u_1)) ↦
                  (↑X.toTop : Type u_1))
                (pullback f g)) →
            (fun
                  (X :
                    CompHausLike fun (X : TopCat) ↦
                      TotallyDisconnectedSpace (↑X : Type u_1) ∧ SecondCountableTopology (↑X : Type u_1)) ↦
                (↑X.toTop : Type u_1))
              S)
        a =
      y

Tactic:
rw [LightProfinite.epi_iff_surjective] at hf

Premises used: LightProfinite.epi_iff_surjective