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In set theory, the union of a collection of sets is the set of all the elements of all the sets of the collection. It is denoted as $A \cup B$.

## Formal DefinitionEdit

Let $A$ be a set.

Let $B$ be a set.

Then, the union of $A$ and $B$ is defined as: $A \cup B = \{ x | x \in A \lor x \in B \}$