空集是指不含任何元素的集合,用表示.由于它具有一些独特的性质,所以空集在解题中占有特殊地位,解题时必须处处注意.下面举例说明.一、要注意空集的两重性空集具有元素的性质,也有集合的属性,所以空集有两重性.如果从“空集是任何集合的子集”这一角度考虑,可以得出∈{};如果将 An empty set refers to a set without any elements, and is used to represent it. Because it has some unique properties, the empty set occupies a special position in solving a problem. When solving a problem, it must be noted everywhere. Here is an example. First, pay attention to the empty set. The two-fold empty set has the nature of the element and also has the set attribute, so the empty set has two properties. If the empty set is considered to be a subset of any set, the ∈{} can be obtained; if