Infinity-Borel Set

Infinity-Borel Set

In set theory, a subset of a Polish space is ∞-Borel if it can be obtained by starting with the open subsets of, and transfinitely iterating the operations of complementation and wellordered union. Note that the set of ∞-Borel sets may not actually be closed under wellordered union; see below.

Read more about Infinity-Borel Set:  Formal Definition, Incorrect Definition, Alternative Characterization

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