∀ (X : SSet) {X_1 Y : SimplexCategoryᵒᵖ} (f : X_1 ⟶ Y),
  CategoryTheory.CategoryStruct.comp (⊤.toSSet.map f) ((fun n => (Equiv.Set.univ (X.obj n)).toIso) Y).hom =
    CategoryTheory.CategoryStruct.comp ((fun n => (Equiv.Set.univ (X.obj n)).toIso) X_1).hom (X.map f)