You're basically right. But isn't there some ambiguity about negative rationals? E.g., what color is -1, and why? Jim On Saturday, April 16, 2016, <rcs@xmission.com> wrote:
It appears that the coloring can be extended to all rationals. --Rich
------------ Quoting James Propp <jamespropp@gmail.com>:
Argh: 355/113 isn't in [0,1]; replace it by 113/355.
Jim
On Friday, April 15, 2016, James Propp <jamespropp@gmail.com> wrote:
There's a unique way to 3-color the rationals in [0,1] using the colors
red, blue, and green so that 0 is red, 1 is blue, and the fractions a/b, c/d, and (a+c)/(b+d) all have distinct colors whenever ad-bc=1.
Puzzle (no spoilers till Sunday please!): What color is 355/113?
Jim Propp
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