Union (set theory)

In set theory, the union (denoted by ∪) of a collection of sets is the set of all elements in the collection.^[1] 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 (${\displaystyle 0}$) sets and it is by definition equal to the empty set.

For explanation of the symbols used in this article, refer to the table of mathematical symbols.