Lengthening structures is what we called inheritance , i . e . , we discover that class descriptions with the same set of methods form a class , and that there is inheritance among the classes of class descriptions 擴展結構就是我們所說的繼承,就是說,我們發現同樣一組方法的類描述形成一個類,并且類描述構成的類之間有繼承關系。