Empty set

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.

Description

Some axiomatic set theories ensure 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.

The empty set may also be called the void set.

See also

• 0 (number)
• Cardinality
• Element (mathematics)
• Inhabited set
• Nothing
• Null set
• Set theory

External links

• Empty set @ Wikipedia