A note on iterative roots of PM functions

In this paper we study iterative roots of PM functions, a special class of non-monotone functions. Problem 2 in [W. Zhang, PM functions, their characteristic intervals and iterative roots, Ann. Polon. Math. LXV (1997) 119–128] is solved partly and Theorem 4 in that paper is generalized. © 2007 Elsevier Inc. All rights reserved