In mathematics, and more specifically set theory, the **empty set** is the unique set having no elements; its size or cardinality (count of elements in a set) is zero. Some axiomatic set theories assure that the empty set exists by including an axiom of empty set; in other theories, its existence can be deduced. Many possible properties of sets are trivially true for the empty set.

*Null set* was once a common synonym for "empty set", but is now a technical term in measure theory.

Read more about Empty Set: Notation, Properties

### Famous quotes containing the words empty and/or set:

“The skylines lit up at dead of night, the air- conditioning systems cooling *empty* hotels in the desert and artificial light in the middle of the day all have something both demented and admirable about them. The mindless luxury of a rich civilization, and yet of a civilization perhaps as scared to see the lights go out as was the hunter in his primitive night.”

—Jean Baudrillard (b. 1929)

“Setting limits gives your child something to define himself against. If you are able to *set* limits without being overly intrusive or controlling, you’ll be providing him with a firm boundary against which he can test his own ideas.”

—Stanley I. Greenspan (20th century)