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Partition of a set: Division into disjoint subsets

To partition a set means to cut it into disjoint pieces.

Formally, a partition of a set \(\; \mathcal{S} \;\) is a set of subsets such that:

  1. No subset \(\; S \;\) is empty.
  2. All subsets are disjoint.
  3. The union of all subsets recovers \(\; \mathcal{S} \;\).