In no sense, apparently! –Dan ----- On Aug 9, 2017 04:32, "Dan Asimov" <dasimov@earthlink.net> wrote: And paradoxically, the conformal bijection z |—> -1/(1+z) of the Riemann sphere S^2 = C u {oo} to itself that preserves the integer points Z^2 ... In what sense does this preserve the integer points? F(17) = -1/18 Andy (i.e., a fractional linear transformation of form z |—> (az + b)/(cz + d), a,b,c,d in Z, ad - bc = 1, i.e., a member of the group PSL(2,Z) = SL(2,Z) / {+-I}) ... is of order three: f(f(f(z))) == z -----