∀ {V : SSet.Truncated 2}
  {x₀ x₁ x₂ : V.obj (Opposite.op { obj := SimplexCategory.mk 0, property := SSet.OneTruncation₂._proof_1 })}
  {e₀₁ : SSet.Truncated.Edge x₀ x₁} {e₁₂ : SSet.Truncated.Edge x₁ x₂} {e₀₂ : SSet.Truncated.Edge x₀ x₂}
  (h : e₀₁.CompStruct e₁₂ e₀₂) {Z : V.HomotopyCategory} (h : SSet.Truncated.HomotopyCategory.mk x₂ ⟶ Z),
  CategoryTheory.CategoryStruct.comp (SSet.Truncated.HomotopyCategory.homMk e₀₁)
      (CategoryTheory.CategoryStruct.comp (SSet.Truncated.HomotopyCategory.homMk e₁₂) h) =
    CategoryTheory.CategoryStruct.comp (SSet.Truncated.HomotopyCategory.homMk e₀₂) h