A well known classical fact is that a Lebesgue measurable function on Euclidean space is almost everywhere equal to a Baire class 2 function. A relatively modern reference for this fact is van Rooij - Schikhof, "A second course on real functions", Cambridge, 1982, p. 143. See also the Math Overflow question here.

What happens in more general situations, say for a measurable function $f$ with respect to a finite regular measure $\mu$ on a locally compact space $X$? Does this have to be equal ae ($\mu$) to some Baire class 2 function on $X$? I think it is true for $X$ compact, because you can use Lusin's theorem to get zero sets $C$ of almost full measure on which $f$ restricted to $C$ is continuous. (Does anyone know of a reference for this?) But for the general locally compact case I think it might not be true.

  • $\begingroup$ Did you mean to answer someone's question? $\endgroup$ – David Roberts Oct 29 '12 at 6:44
  • $\begingroup$ My initial post was an accident $\endgroup$ – Fred Dashiell Oct 29 '12 at 7:03

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