| Specifically, the number of ways a set with n objects can be partitioned into disjoint and non-empty subsets is described by the Bell numbers. |
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| A split is a partition of the set of taxa into two disjoint, non-empty groups. |
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| We can understand nothing by making it a thing, the empty set for example, but without some thing to contrast it with, non-empty sets, the thing no longer makes sense. |
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