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Disjoint sets

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Two sets are said to be disjoint if they have no element in common. For example, \{1,2,3,4\} and \{5,6,7,8\} are disjoint sets, while \{1, 2, 3\} and \{2, 4, 6\} are not disjoint.

Disjointness can be generalized to several sets in more than one way. One possibility is the notion of pairwise disjoint: a number of sets are pairwise disjoint if every pair of the sets are disjoint. For example, the three sets \{1, 2\}, \{3, 4\} and \{5, 6\} are pairwise disjoint. Alternatively, one can ask for the weaker condition that the sets have empty intersection. For instance, the three sets \{1, 2\}, \{1, 3\} and \{2, 4\} have empty intersection but are not pairwise disjoint.

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