F-sigma subset

Symbol-free definition
A subset of a topological space is termed a $$F_\sigma$$-subset if it satisfies the following equivalent conditions:


 * Its complement is a $$G_\delta$$ subset (
 * It is expressible as a countable union of closed subsets of the topological space

Stronger properties

 * Closed subset

Related properties

 * G-delta subset

See F hierarchy and G hierarchy