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sigma-algebra, sigma algebra, $\sigma$ algebra, Borel structure, $\sigma$-field, sigma-field, sigma field, $\sigma$ field
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In relation to Djao's entry \sigma-algebra, \emptyset \in \mathcal{B}(E) appears like a premise. As far as I know, \emptyset \in A \forall A. So, why this one is not redundant?
BTW, in my browser IE6 the entry title looks like [red cross]$\sigma$-algebra, missing the greek letter sigma.

You seem to be confusing membership with inclusion (being a subset of). The empty set is a subset of every set, but it is not, for example, a member of itself.

Hi ratboy,
Yes! Now it is clearer for me why E \in \mathcal{B(E)}.
Thank you!

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