{X : SSet} →
  (f₀ f₂ f₃ : SSet.stdSimplex.obj { len := 2 } ⟶ X) →
    CategoryTheory.CategoryStruct.comp (SSet.stdSimplex.δ 2) f₀ =
        CategoryTheory.CategoryStruct.comp (SSet.stdSimplex.δ 0) f₃ →
      CategoryTheory.CategoryStruct.comp (SSet.stdSimplex.δ 1) f₀ =
          CategoryTheory.CategoryStruct.comp (SSet.stdSimplex.δ 0) f₂ →
        CategoryTheory.CategoryStruct.comp (SSet.stdSimplex.δ 2) f₂ =
            CategoryTheory.CategoryStruct.comp (SSet.stdSimplex.δ 2) f₃ →
          ((SSet.horn 3 1).toSSet ⟶ X)