411 REFERENCE · Wiktionary
Fσ
Reference material by Wiktionary contributors. This retains its source identity and is not 411 news reporting.
Translingual
Fσ set
Etymology
From mul fr fermé closed for the 'F' and French fr somme sum for the 'σ'. The 'σ' can be interpreted to mean "countable union."
Symbol
mul symbol Fσ
mul analysis topology A countable union of closed sets.
Hypernyms
mul Borel set
mul Measure theory