Union (set theory)

Set of elements in any of some sets

In set theory, the union (denoted by ∪) of a collection of sets is the set of all elements in the collection. It is one of the fundamental operations through which sets can be combined and related to each other. A nullary union refers to a union of zero (⁠ 0 {\displaystyle 0} ⁠) sets and it is by definition equal to the empty set.

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