F_σ

Translingual

Wikipedia has an article on:

Fσ set

Wikipedia

Etymology

From French fermé (“closed”) for the 'F' and French somme (“sum”) for the 'σ'. The 'σ' can be interpreted to mean "countable union."

Symbol

F_σ

1. (analysis) A countable union of closed sets.

Hypernyms

• Borel set