The Group of Automorphisms of the Function Fields of the Curve
xn+ym-1=0
(link to Ideal)
.
MR 2000f:12005
Journal of Number Theory, v 72, n 1, September 1998, p 110-136
The group of Automorphisms Of Cyclic Extensions of Ration
al Function Fields. Journal of Algebra Volume 216 Number 2, June 15, 1999, p. 665-706 ps - pdf MR 99f:11074