On equivalent representations of infinite structures

Abstract

According to Barthelman and Blumensath, the following families of infinite graphs are isomorphic: (1) prefix-recognisable graphs, (2) graph solutions of VR equational systems and (3) MS interpretations of regular trees. In this paper, we consider the extension of prefix-recognisable graphs to prefix-recognisable structures and of graphs solutions of VR equational systems to structures solutions of positive quantifier free definable (PQFD) equational systems. We extend Barthelman and Blumensath's result to structures parameterised by infinite graphs by proving that the following families of structures are equivalent: (1) prefix-recognisable structures restricted by a language accepted by an infinite deterministic automaton, (2) solutions of infinite PQFD equational systems and (3) MS interpretations of the unfoldings of infinite deterministic graphs. Furthermore, we show that the addition of a fuse operator, that merges several vertices together, to PQFD equational systems does not increase their expressive power. © Springer-Verlag Berlin Heidelberg 2003.