| Let S1 denote the circle. In this paper, we show the following.Theorem. Let f: S1→S1 be a continuous map and suppose f has a fixed point and the set of periodic points of f is closed, then the period of each periodic point of f is a power of 2.Corollary. Let f: S1→S1 be a continuous map and suppose the set of periodic points of f is closed, then there exists an odd integer m such that the set of periods of periodic points of f is contained in the set {m·2n; n = 0,1,2,…}. |
