The study of definable sets and functions in polish spaces.
Descriptive Set Theory
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References
Becker, H. and Kechris, A. S. The Descriptive Set Theory of Polish Group Actions. New York: Cambridge University Press, 1996.Referenced on Wolfram|Alpha
Descriptive Set TheoryCite this as:
Weisstein, Eric W. "Descriptive Set Theory." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/DescriptiveSetTheory.html