空集不是无,是内部没有元素的集合,而集合就是有,这通常是初学者的一个难点。将集合想象成一个装有元素的袋子的想法或许有帮助,袋子可以是空的,但袋子本身确实存在。我们可以从三个方面加以理解:一、是集合;二、没有元素或元素个数为零;三、在没有元素的集合中唯一。 Empty set is not without, is not a collection of elements inside, and the collection is there, which is usually a difficulty for beginners. It may be helpful to think of a collection as a bag with elements, but the bag can be empty, but the bag itself does exist. We can understand from three aspects: First, is a collection; Second, there is no element or element number is zero; Third, there is no element in the collection only.