Groups and Semigroups Generated by Automata

Authors

David McCune, University of Nebraska-LincolnFollow

Date of this Version

5-2011

Document Type

Article

Comments

A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfilment of Requirements For the Degree of Doctor of Philosophy, Major: Mathematics, Under the Supervision of Professor Susan Hermiller and Professor John Meakin. Lincoln, Nebraska: May, 2011
Copyright 2011 David McCune

Abstract

In this dissertation we classify the metabelian groups arising from a restricted class of invertible synchronous automata over a binary alphabet. We give faithful, self-similar actions of Heisenberg groups and upper triangular matrix groups. We introduce a new class of semigroups given by a restricted class of asynchronous automata. We call these semigroups ``expanding automaton semigroups''. We show that this class strictly contains the class of automaton semigroups, and we show that the class of asynchronous automaton semigroups strictly contains the class of expanding automaton semigroups. We demonstrate that undecidability arises in the actions of expanding automaton semigroups and semigroups arising from asynchronous automata on regular rooted trees. In particular, we show that one cannot decide whether or not an element of an asynchronous automaton semigroup has a fixed point. We show that expanding automaton semigroups are residually finite, while semigroups given by asynchronous automata need not be. We show that the class of expanding automaton semigroups is not closed under taking normal ideal extensions, but the class of semigroups given by asynchronous automata is closed under taking normal ideal extensions. We show that the class of expanding automaton semigroups is closed under taking direct products, provided that the direct product is finitely generated. We show that the class of automaton semigroups is not closed under passing to residually finite Rees quotients. We show that every partially commutative monoid is an automaton semigroup, and every partially commutative semigroup is an expanding automaton semigroup.