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We characterize the infinite words determined by one-way stack automata. An infinite language L determines an infinite word alpha if every string in L is a prefix of alpha. If L is regular or context-free, it is known that alpha must be ultimately periodic. We extend this result to the class of languages recognized by one-way nondeterministic checking stack automata (1-NCSA). We then consider stronger classes of stack automata and show that they determine a class of infinite words which we call multilinear. We show that every multilinear word can be written in a form which is amenable to parsing. Finally, we consider the class of one-way multihead deterministic finite automata (1:multi-DFA). We show that every multilinear word can be determined by some 1:multi-DFA, but that there exist infinite words determined by 1:multi-DFA which are not multilinear.
@InProceedings{smith:LIPIcs.FSTTCS.2013.413,
author = {Smith, Tim},
title = {{On Infinite Words Determined by Stack Automata}},
booktitle = {IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2013)},
pages = {413--424},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-939897-64-4},
ISSN = {1868-8969},
year = {2013},
volume = {24},
editor = {Seth, Anil and Vishnoi, Nisheeth K.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2013.413},
URN = {urn:nbn:de:0030-drops-43692},
doi = {10.4230/LIPIcs.FSTTCS.2013.413},
annote = {Keywords: stack automaton, infinite word, pumping lemma, prefix language, multihead finite automaton}
}