87 partitioning: The division of a set into subsets such that each element of the set is in exactly one of the subsets.
87 partitioning: The division of a set into subsets such that each element of the set is in exactly one of the subsets.
分割：一个集合分割为子集，集合中的每一个元素都唯一的存在于某一个子集中。