FOM: ReplyToMarker

Harvey Friedman friedman at
Mon Nov 10 22:03:16 EST 1997

Marker writes:

>A) Let E be a Borel subset of the unit square in the plane, which is symmetric
>about the line y = x. Then E contains or is disjoint from the graph of a
>Borel measurable function.
>Harvey showed that A) is true but not provable in (or well beyond) second
>order arithmetic.

In my response to Marker 11/7/97 which I made on 11/10/97, I carelessly
forgot to add:

***And therefore by earlier results of Martin and myself, A) is equivalent
to Borel Determinacy. This works over weak fragments of second order

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