Perpetual points and periodic perpetual loci in maps
  We introduce the concepts of perpetual points and periodic perpetual loci in discrete--time systems (maps). The occurrence and analysis of these points/loci are shown and basic examples are considered. We discuss the potential usage and properties of introduced concepts. The comparison of perpetual points and loci in discrete--time and continuous--time systems is presented. Discussed methods can be widely applied in other dynamical systems. 
Dawid Dudkowski, Awadhesh Prasad, Tomasz Kapitaniak
nlin.CD