Dynamics of annulus maps II: periodic points for coverings.

Let f be a covering map of the open annulus A = S 1 ×(0, 1) of degree d, |d| > 1. Assume that f preserves an essential (i.e not contained in a disk of A) compact subset K. We show that f has at least the same number of periodic points in each period as the map z d on S 1 .