# F-sigma

From Encyclopedia of Mathematics

2020 Mathematics Subject Classification: *Primary:* 28A05 [MSN][ZBL]

In a topological space $X$ a subset which is the countable union of closed sets. See Borel set and also G-delta.

**How to Cite This Entry:**

F-sigma.

*Encyclopedia of Mathematics.*URL: http://encyclopediaofmath.org/index.php?title=F-sigma&oldid=27668