  We study upper bounds on the order of automorphisms of non-singular curves
$X$ satisfying at least one of the following hypothesis: 1) $X$ is an
$m$-sheeted covering of exactly one non-singular curve of genus $\gamma$, where
$m$ is prime; 2) the center of the group of automorphisms of $X$ is
non-trivial.

Algebraic Geometry;Algebraic Geometry