The story
The 'σ' stands for "countable union".
Etymology from Wiktionary, CC BY-SA 4.0.
σ-compact
Today it means: That is expressible as a countable union of compact sets. Full definition →
Today it means: That is expressible as a countable union of compact sets. Full definition →
The 'σ' stands for "countable union".
Etymology from Wiktionary, CC BY-SA 4.0.