What the meaning of $\sigma$ (s) in $\sigma$-algebra?
By Daniel Rodriguez •
Why a mathematician write a "s"/$\sigma$ in $\sigma$-algebra in place of another letter? Does it have anything to do with the word "sum", like $\Sigma$ or $\int$ for a sum?
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$\begingroup$Kenny Wong is right.
This notation came to us from German mathematicians around 1900. (Maybe Hausdorff was the first to use it? I don't remember.) The Greek letters $\sigma$ and $\delta$ denoted (closed under, or constructed by) countable unions and countable intersections, repectively.
The Greek letter $\sigma$ corresponts to the Latin letter $S$, which is the initial of the German word Summe, meaning union.
The Greek letter $\delta$ corresponts to the Latin letter $D$, which is the initial of the German word Durchschnitt, meaning intersection.
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