M is called taxonomic class of sets if. for every two elements of m, either they are disjoint, or one is a subset of the other.
若m中任意两个子集，或者它们无共同元素，或者一个是另一个的子集，这样的M称为分类集。
M is called taxonomic class of sets if. for every two elements of m, either they are disjoint, or one is a subset of the other.
若m中任意两个子集，或者它们无共同元素，或者一个是另一个的子集，这样的M称为分类集。
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