# Definition:Class Union

## Definition

Let $A$ and $B$ be two classes.

The (class) union $A \cup B$ of $A$ and $B$ is defined as the class of all sets $x$ such that either $x \in A$ or $x \in B$ or both:

$x \in A \cup B \iff x \in A \lor x \in A$

or:

$A \cup B = \set {x: x \in A \lor x \in B}$

### General Definition

Let $A$ be a class.

The union of $A$ is:

$\ds \bigcup A := \set {x: \exists y: x \in y \land y \in A}$

That is, the class of all elements of all elements of $A$ which are themselves sets.

## Also see

• Results about class unions can be found here.

## Internationalization

Union is translated:

 In French: somme (literally: sum) In French: union In French: réunion In Dutch: vereniging