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集合的子集可以含集合中的任意元素,甚至可以是空集,所以集合中的每個元素都可以有選或不選的可能.每個元素都有兩個選擇.含有n種元素的集合中,子集是2x2x……x2即2^n個. 非空子集有2^n-1個(减去空集). 非空真子集有2^n-2個(减去空集和集合本身).
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