Module: Mathlib.CategoryTheory.Extensive

Goal state before:
pp: case fac_left
J : Type v'
inst✝² : Category.{u', v'} J
C : Type u
inst✝¹ : Category.{v, u} C
D : Type u''
inst✝ : Category.{v'', u''} D
X Y : C
Z : Type u
f : Z ⟶ (Types.binaryCoproductCocone PUnit.{u + 1} PUnit.{u + 1}).pt
this :
  ∀ (x : (fun X ↦ X) Z),
    (ConcreteCategory.hom f) x = Sum.inl PUnit.unit ∨ (ConcreteCategory.hom f) x = Sum.inr PUnit.unit
eX : { p // (ConcreteCategory.hom f) p.1 = Sum.inl p.2 } ≃ { x // (ConcreteCategory.hom f) x = Sum.inl PUnit.unit } :=
  { toFun := fun p ↦ ⟨(↑p).1, ⋯⟩, invFun := fun x ↦ ⟨(x.1, PUnit.unit), ⋯⟩, left_inv := ⋯, right_inv := ⋯ }
eY : { p // (ConcreteCategory.hom f) p.1 = Sum.inr p.2 } ≃ { x // (ConcreteCategory.hom f) x = Sum.inr PUnit.unit } :=
  { toFun := fun p ↦ ⟨(↑p).1, ⋯⟩, invFun := fun x ↦ ⟨(x.1, PUnit.unit), ⋯⟩, left_inv := ⋯, right_inv := ⋯ }
s : BinaryCofan (Types.PullbackObj f (↾Sum.inl)) (Types.PullbackObj f (↾Sum.inr))
x : Z
property✝ : (ConcreteCategory.hom f) (x, PUnit.unit).1 = (ConcreteCategory.hom (↾Sum.inl)) (x, PUnit.unit).2
⊢ (if h : (ConcreteCategory.hom f) x = Sum.inl PUnit.unit then (ConcreteCategory.hom s.inl) (eX.symm ⟨x, h⟩)
    else (ConcreteCategory.hom s.inr) (eY.symm ⟨x, ⋯⟩)) =
    (ConcreteCategory.hom s.inl) ⟨(x, PUnit.unit), property✝⟩

Tactic:
split_ifs with h

Goal state after:
case pos
J : Type v'
inst✝² : Category.{u', v'} J
C : Type u
inst✝¹ : Category.{v, u} C
D : Type u''
inst✝ : Category.{v'', u''} D
X Y : C
Z : Type u
f : Z ⟶ (Types.binaryCoproductCocone PUnit.{u + 1} PUnit.{u + 1}).pt
this :
  ∀ (x : (fun X ↦ X) Z),
    (ConcreteCategory.hom f) x = Sum.inl PUnit.unit ∨ (ConcreteCategory.hom f) x = Sum.inr PUnit.unit
eX : { p // (ConcreteCategory.hom f) p.1 = Sum.inl p.2 } ≃ { x // (ConcreteCategory.hom f) x = Sum.inl PUnit.unit } :=
  { toFun := fun p ↦ ⟨(↑p).1, ⋯⟩, invFun := fun x ↦ ⟨(x.1, PUnit.unit), ⋯⟩, left_inv := ⋯, right_inv := ⋯ }
eY : { p // (ConcreteCategory.hom f) p.1 = Sum.inr p.2 } ≃ { x // (ConcreteCategory.hom f) x = Sum.inr PUnit.unit } :=
  { toFun := fun p ↦ ⟨(↑p).1, ⋯⟩, invFun := fun x ↦ ⟨(x.1, PUnit.unit), ⋯⟩, left_inv := ⋯, right_inv := ⋯ }
s : BinaryCofan (Types.PullbackObj f (↾Sum.inl)) (Types.PullbackObj f (↾Sum.inr))
x : Z
property✝ : (ConcreteCategory.hom f) (x, PUnit.unit).1 = (ConcreteCategory.hom (↾Sum.inl)) (x, PUnit.unit).2
h : (ConcreteCategory.hom f) x = Sum.inl PUnit.unit
⊢ (ConcreteCategory.hom s.inl) (eX.symm ⟨x, h⟩) = (ConcreteCategory.hom s.inl) ⟨(x, PUnit.unit), property✝⟩

case neg
J : Type v'
inst✝² : Category.{u', v'} J
C : Type u
inst✝¹ : Category.{v, u} C
D : Type u''
inst✝ : Category.{v'', u''} D
X Y : C
Z : Type u
f : Z ⟶ (Types.binaryCoproductCocone PUnit.{u + 1} PUnit.{u + 1}).pt
this :
  ∀ (x : (fun X ↦ X) Z),
    (ConcreteCategory.hom f) x = Sum.inl PUnit.unit ∨ (ConcreteCategory.hom f) x = Sum.inr PUnit.unit
eX : { p // (ConcreteCategory.hom f) p.1 = Sum.inl p.2 } ≃ { x // (ConcreteCategory.hom f) x = Sum.inl PUnit.unit } :=
  { toFun := fun p ↦ ⟨(↑p).1, ⋯⟩, invFun := fun x ↦ ⟨(x.1, PUnit.unit), ⋯⟩, left_inv := ⋯, right_inv := ⋯ }
eY : { p // (ConcreteCategory.hom f) p.1 = Sum.inr p.2 } ≃ { x // (ConcreteCategory.hom f) x = Sum.inr PUnit.unit } :=
  { toFun := fun p ↦ ⟨(↑p).1, ⋯⟩, invFun := fun x ↦ ⟨(x.1, PUnit.unit), ⋯⟩, left_inv := ⋯, right_inv := ⋯ }
s : BinaryCofan (Types.PullbackObj f (↾Sum.inl)) (Types.PullbackObj f (↾Sum.inr))
x : Z
property✝ : (ConcreteCategory.hom f) (x, PUnit.unit).1 = (ConcreteCategory.hom (↾Sum.inl)) (x, PUnit.unit).2
h : ¬(ConcreteCategory.hom f) x = Sum.inl PUnit.unit
⊢ (ConcreteCategory.hom s.inr) (eY.symm ⟨x, ⋯⟩) = (ConcreteCategory.hom s.inl) ⟨(x, PUnit.unit), property✝⟩