9 Feb
2016
9 Feb
'16
10:16 p.m.
On Mon, Feb 8, 2016 at 1:35 PM, Warren D Smith <warren.wds@gmail.com> wrote:
More interesting question: Find a function F(x), which is continuous (the smoother the better) which maps rationals to rationals, but is not a rational function.
F(x) = |x|^n takes rationals to rationals for any positive integer n, is not a rational function when n is odd, and is n times differentiable, so you can make it as smooth as you like by making n large enough. Andy Latto andy.latto@pobox.com