FOM: categorical dis-foundations

[Martin Davis]

At 04:37 PM 2/2/98 -0800, Vaughan Pratt wrote:
>
>if such monsters [i.e., the function which is 0 on Q and 1 on R-Q] can even
be >considered part of analysis.
>

This "monster" (or rather its restriction to [0,1]) is the standard example
of a Lebesgue integrable function not Riemann integrable. It is of Baire
class 2 with a simple expression as a limit. I believe (but am not certain)
that it is due to Dirichlet.

Martin