Finite Automata Over Infinite Alphabets: Two Models with Transitions for Local Change

Abstract

Two models of automata over infinite alphabets are presented, mainly with a focus on the alphabet [Formula: see text]. In the first model, transitions can refer to logic formulas that connect properties of successive letters. In the second, the letters are considered as columns of a labeled grid which an automaton traverses column by column. Thus, both models focus on the comparison of successive letters, i.e. “local changes”. We prove closure (and non-closure) properties, show the decidability of the respective non-emptiness problems, prove limits on decidability results for extended models, and discuss open issues in the development of a generalized theory.