17 Apr
2016
17 Apr
'16
4:41 a.m.
Keith Lynch was the first to solve this puzzle (or at least the first to email me a solution). Rich Schroeppel pointed out that the restriction to [0,1] is unnecessary. It's now Sunday where I am, so Keith and others may post freely. Jim Propp 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