Automata on ordinals and linear orders

Abstract

We investigate structures recognizable by α-automata with running time a limit ordinal α. The domain of such a structure consists of finite α-words with gaps. An α-automaton resembles a finite automaton but has a limit rule which maps the set of states which appear cofinally often before the limit to a limit state. We determine the suprema of the α-automatic ordinals and the ranks of α-automatic linear orders. The power of α-automata increases with every power of ω. © 2011 Springer-Verlag.