Module: Mathlib.AlgebraicTopology.SimplicialSet.HornColimits

Goal state before:
pp: X : SSet
f₀ f₂ f₃ : Δ[2] ⟶ X
h₁₂ : stdSimplex.δ 2 ≫ f₀ = stdSimplex.δ 0 ≫ f₃
h₁₃ : stdSimplex.δ 1 ≫ f₀ = stdSimplex.δ 0 ≫ f₂
h₂₃ : stdSimplex.δ 2 ≫ f₂ = stdSimplex.δ 2 ≫ f₃
x : ↑{x | x.1 < x.2}
⊢ (Subcomplex.homOfLE ⋯ ≫
      match ↑(↑x).1, ⋯ with
      | 0, hi => (stdSimplex.faceSingletonComplIso 0).inv ≫ f₀
      | 1, hi => ⋯.elim
      | 2, hi => (stdSimplex.faceSingletonComplIso 2).inv ≫ f₂
      | 3, hi => (stdSimplex.faceSingletonComplIso 3).inv ≫ f₃) =
    Subcomplex.homOfLE ⋯ ≫
      match ↑(↑x).2, ⋯ with
      | 0, hi => (stdSimplex.faceSingletonComplIso 0).inv ≫ f₀
      | 1, hi => ⋯.elim
      | 2, hi => (stdSimplex.faceSingletonComplIso 2).inv ≫ f₂
      | 3, hi => (stdSimplex.faceSingletonComplIso 3).inv ≫ f₃

Tactic:
fin_cases x

Goal state after:
case «0»
X : SSet
f₀ f₂ f₃ : Δ[2] ⟶ X
h₁₂ : stdSimplex.δ 2 ≫ f₀ = stdSimplex.δ 0 ≫ f₃
h₁₃ : stdSimplex.δ 1 ≫ f₀ = stdSimplex.δ 0 ≫ f₂
h₂₃ : stdSimplex.δ 2 ≫ f₂ = stdSimplex.δ 2 ≫ f₃
⊢ (Subcomplex.homOfLE ⋯ ≫
      match ↑(↑⟨(⟨(fun i ↦ i) ⟨0, ⋯⟩, ⋯⟩, ⟨(fun i ↦ i) ⟨2, ⋯⟩, ⋯⟩), ⋯⟩).1, ⋯ with
      | 0, hi => (stdSimplex.faceSingletonComplIso 0).inv ≫ f₀
      | 1, hi => ⋯.elim
      | 2, hi => (stdSimplex.faceSingletonComplIso 2).inv ≫ f₂
      | 3, hi => (stdSimplex.faceSingletonComplIso 3).inv ≫ f₃) =
    Subcomplex.homOfLE ⋯ ≫
      match ↑(↑⟨(⟨(fun i ↦ i) ⟨0, ⋯⟩, ⋯⟩, ⟨(fun i ↦ i) ⟨2, ⋯⟩, ⋯⟩), ⋯⟩).2, ⋯ with
      | 0, hi => (stdSimplex.faceSingletonComplIso 0).inv ≫ f₀
      | 1, hi => ⋯.elim
      | 2, hi => (stdSimplex.faceSingletonComplIso 2).inv ≫ f₂
      | 3, hi => (stdSimplex.faceSingletonComplIso 3).inv ≫ f₃

case «1»
X : SSet
f₀ f₂ f₃ : Δ[2] ⟶ X
h₁₂ : stdSimplex.δ 2 ≫ f₀ = stdSimplex.δ 0 ≫ f₃
h₁₃ : stdSimplex.δ 1 ≫ f₀ = stdSimplex.δ 0 ≫ f₂
h₂₃ : stdSimplex.δ 2 ≫ f₂ = stdSimplex.δ 2 ≫ f₃
⊢ (Subcomplex.homOfLE ⋯ ≫
      match ↑(↑⟨(⟨(fun i ↦ i) ⟨0, ⋯⟩, ⋯⟩, ⟨(fun i ↦ i) ⟨3, ⋯⟩, ⋯⟩), ⋯⟩).1, ⋯ with
      | 0, hi => (stdSimplex.faceSingletonComplIso 0).inv ≫ f₀
      | 1, hi => ⋯.elim
      | 2, hi => (stdSimplex.faceSingletonComplIso 2).inv ≫ f₂
      | 3, hi => (stdSimplex.faceSingletonComplIso 3).inv ≫ f₃) =
    Subcomplex.homOfLE ⋯ ≫
      match ↑(↑⟨(⟨(fun i ↦ i) ⟨0, ⋯⟩, ⋯⟩, ⟨(fun i ↦ i) ⟨3, ⋯⟩, ⋯⟩), ⋯⟩).2, ⋯ with
      | 0, hi => (stdSimplex.faceSingletonComplIso 0).inv ≫ f₀
      | 1, hi => ⋯.elim
      | 2, hi => (stdSimplex.faceSingletonComplIso 2).inv ≫ f₂
      | 3, hi => (stdSimplex.faceSingletonComplIso 3).inv ≫ f₃

case «2»
X : SSet
f₀ f₂ f₃ : Δ[2] ⟶ X
h₁₂ : stdSimplex.δ 2 ≫ f₀ = stdSimplex.δ 0 ≫ f₃
h₁₃ : stdSimplex.δ 1 ≫ f₀ = stdSimplex.δ 0 ≫ f₂
h₂₃ : stdSimplex.δ 2 ≫ f₂ = stdSimplex.δ 2 ≫ f₃
⊢ (Subcomplex.homOfLE ⋯ ≫
      match ↑(↑⟨(⟨(fun i ↦ i) ⟨2, ⋯⟩, ⋯⟩, ⟨(fun i ↦ i) ⟨3, ⋯⟩, ⋯⟩), ⋯⟩).1, ⋯ with
      | 0, hi => (stdSimplex.faceSingletonComplIso 0).inv ≫ f₀
      | 1, hi => ⋯.elim
      | 2, hi => (stdSimplex.faceSingletonComplIso 2).inv ≫ f₂
      | 3, hi => (stdSimplex.faceSingletonComplIso 3).inv ≫ f₃) =
    Subcomplex.homOfLE ⋯ ≫
      match ↑(↑⟨(⟨(fun i ↦ i) ⟨2, ⋯⟩, ⋯⟩, ⟨(fun i ↦ i) ⟨3, ⋯⟩, ⋯⟩), ⋯⟩).2, ⋯ with
      | 0, hi => (stdSimplex.faceSingletonComplIso 0).inv ≫ f₀
      | 1, hi => ⋯.elim
      | 2, hi => (stdSimplex.faceSingletonComplIso 2).inv ≫ f₂
      | 3, hi => (stdSimplex.faceSingletonComplIso 3).inv ≫ f₃