27 research outputs found
Automatic Quotients of Free Groups
Automatic groups admitting prefix closed automatic structures with uniqueness
are characterized as the quotients of free groups by normal subgroups
possessing sets of free generators satisfying certain language-theoretic
conditions.Comment: 14 pages, no figures. Minor corrections. Statements of theorems and
lemmas are unchange
The Automatic Baire Property and an Effective Property of ω-Rational Functions
International audienceWe prove that ω-regular languages accepted by Büchi or Muller automata satisfy an effective automata-theoretic version of the Baire property. Then we use this result to obtain a new effective property of rational functions over infinite words which are realized by finite state Büchi transducers: for each such function F : Σ^ω → Γ^ω , one can construct a deterministic Büchi automaton A accepting a dense Π^0_2-subset of Σ^ω such that the restriction of F to L(A) is continuous
The monoid of queue actions
We investigate the monoid of transformations that are induced by sequences of
writing to and reading from a queue storage. We describe this monoid by means
of a confluent and terminating semi-Thue system and study some of its basic
algebraic properties, e.g., conjugacy. Moreover, we show that while several
properties concerning its rational subsets are undecidable, their uniform
membership problem is NL-complete. Furthermore, we present an algebraic
characterization of this monoid's recognizable subsets. Finally, we prove that
it is not Thurston-automatic
Highly Undecidable Problems For Infinite Computations
We show that many classical decision problems about 1-counter
omega-languages, context free omega-languages, or infinitary rational
relations, are -complete, hence located at the second level of the
analytical hierarchy, and "highly undecidable". In particular, the universality
problem, the inclusion problem, the equivalence problem, the determinizability
problem, the complementability problem, and the unambiguity problem are all
-complete for context-free omega-languages or for infinitary rational
relations. Topological and arithmetical properties of 1-counter
omega-languages, context free omega-languages, or infinitary rational
relations, are also highly undecidable. These very surprising results provide
the first examples of highly undecidable problems about the behaviour of very
simple finite machines like 1-counter automata or 2-tape automata.Comment: to appear in RAIRO-Theoretical Informatics and Application
The Automatic Baire Property and An Effective Property of ω-Rational Functions
We prove that -regular languages accepted by B\"uchi or Muller automata satisfy an effective automata-theoretic version of the Baire property. Then we use this result to obtain a new effective property of rational functions over infinite words which are realized by finite state B\"uchi transducers: for each such function , one can construct a deterministic B\"uchi automaton accepting a dense -subset of such that the restriction of to is continuous