17 research outputs found
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 Determinacy of Context-Free Games
We prove that the determinacy of Gale-Stewart games whose winning sets are
accepted by real-time 1-counter B\"uchi automata is equivalent to the
determinacy of (effective) analytic Gale-Stewart games which is known to be a
large cardinal assumption. We show also that the determinacy of Wadge games
between two players in charge of omega-languages accepted by 1-counter B\"uchi
automata is equivalent to the (effective) analytic Wadge determinacy. Using
some results of set theory we prove that one can effectively construct a
1-counter B\"uchi automaton A and a B\"uchi automaton B such that: (1) There
exists a model of ZFC in which Player 2 has a winning strategy in the Wadge
game W(L(A), L(B)); (2) There exists a model of ZFC in which the Wadge game
W(L(A), L(B)) is not determined. Moreover these are the only two possibilities,
i.e. there are no models of ZFC in which Player 1 has a winning strategy in the
Wadge game W(L(A), L(B)).Comment: To appear in the Proceedings of the 29 th International Symposium on
Theoretical Aspects of Computer Science, STACS 201
The Complexity of Infinite Computations In Models of Set Theory
We prove the following surprising result: there exist a 1-counter B\"uchi
automaton and a 2-tape B\"uchi automaton such that the \omega-language of the
first and the infinitary rational relation of the second in one model of ZFC
are \pi_2^0-sets, while in a different model of ZFC both are analytic but non
Borel sets.
This shows that the topological complexity of an \omega-language accepted by
a 1-counter B\"uchi automaton or of an infinitary rational relation accepted by
a 2-tape B\"uchi automaton is not determined by the axiomatic system ZFC.
We show that a similar result holds for the class of languages of infinite
pictures which are recognized by B\"uchi tiling systems.
We infer from the proof of the above results an improvement of the lower
bound of some decision problems recently studied by the author
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 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
Wadge Degrees of -Languages of Petri Nets
We prove that -languages of (non-deterministic) Petri nets and
-languages of (non-deterministic) Turing machines have the same
topological complexity: the Borel and Wadge hierarchies of the class of
-languages of (non-deterministic) Petri nets are equal to the Borel and
Wadge hierarchies of the class of -languages of (non-deterministic)
Turing machines which also form the class of effective analytic sets. In
particular, for each non-null recursive ordinal there exist some -complete and some -complete -languages of Petri nets, and the supremum of
the set of Borel ranks of -languages of Petri nets is the ordinal
, which is strictly greater than the first non-recursive ordinal
. We also prove that there are some -complete, hence non-Borel, -languages of Petri nets, and
that it is consistent with ZFC that there exist some -languages of
Petri nets which are neither Borel nor -complete. This
answers the question of the topological complexity of -languages of
(non-deterministic) Petri nets which was left open in [DFR14,FS14].Comment: arXiv admin note: text overlap with arXiv:0712.1359, arXiv:0804.326
Some Problems in Automata Theory Which Depend on the Models of Set Theory
We prove that some fairly basic questions on automata reading infinite words
depend on the models of the axiomatic system ZFC. It is known that there are
only three possibilities for the cardinality of the complement of an
omega-language accepted by a B\"uchi 1-counter automaton . We prove
the following surprising result: there exists a 1-counter B\"uchi automaton
such that the cardinality of the complement of the omega-language
is not determined by ZFC: (1). There is a model of ZFC in which
is countable. (2). There is a model of ZFC in which has
cardinal . (3). There is a model of ZFC in which
has cardinal with . We prove a very
similar result for the complement of an infinitary rational relation accepted
by a 2-tape B\"uchi automaton . As a corollary, this proves that the
Continuum Hypothesis may be not satisfied for complements of 1-counter
omega-languages and for complements of infinitary rational relations accepted
by 2-tape B\"uchi automata. We infer from the proof of the above results that
basic decision problems about 1-counter omega-languages or infinitary rational
relations are actually located at the third level of the analytical hierarchy.
In particular, the problem to determine whether the complement of a 1-counter
omega-language (respectively, infinitary rational relation) is countable is in
. This is rather surprising if
compared to the fact that it is decidable whether an infinitary rational
relation is countable (respectively, uncountable).Comment: To appear in the journal RAIRO-Theoretical Informatics and
Application