Why do we talk of sigma algebras in measure theory. As far as I know sigma is related to the countability. But what does it stand for?
2026-04-06 20:58:15.1775509095
Sigma Algebra: Etymology
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Ok I got it: An algebra in the sense of sets is meant to be a boolean algebra w.r.t. union, intersection, complementation plus the empty set and the universe. In this setting goin to countability raises both intersections and unions so theres no need to be more precise so we can simply say sigma algebra without refering to intersections or unions.
Sigma in this setting then has the meaning of countable rather than "summe" as the german word for union...
Besides talkin of countable complementations has no meaning, anyway.