@article{BordihnFernauHolzeretal.2006,
  author    = {Bordihn, Henning and Fernau, Henning and Holzer, Markus and Manca, Vincenzo and Martin-Vide, Carlos},
  title     = {Iterated sequential transducers as language generating devices},
  series = {Theoretical computer science},
  volume    = {369},
  journal   = {Theoretical computer science},
  number    = {1},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0304-3975},
  doi       = {10.1016/j.tcs.2006.07.059},
  pages     = {67 -- 81},
  year      = {2006},
  abstract  = {Iterated finite state sequential transducers are considered as language generating devices. The hierarchy induced by the size of the state alphabet is proved to collapse to the fourth level. The corresponding language families are related to the families of languages generated by Lindenmayer systems and Chomsky grammars. Finally, some results on deterministic and extended iterated finite state transducers are established.},
  language  = {en}
}
@article{Bordihn2005,
  author    = {Bordihn, Henning},
  title     = {On the number of components in cooperating distributed grammar systems},
  issn      = {0304-3975},
  year      = {2005},
  abstract  = {It is proved that the number of components in context-free cooperating distributed (CD) grammar systems can be reduced to 3 when they are working in the so-called sf-mode of derivation, which is the cooperation protocol which has been considered first for CD grammar systems. In this derivation mode, a component continues the derivation until and unless there is a nonterminal in the sentential form which cannot be rewritten according to that component. Moreover, it is shown that CD grammar systems in sf-mode with only one component can generate only the context-free languages but they can generate non-context-free languages if two components are used. The sf-mode of derivation is compared with other well-known cooperation protocols with respect to the hierarchies induced by the number of components. (C) 2004 Elsevier B.V. All rights reserved},
  language  = {en}
}
@article{BordihnHolzerKutrib2005,
  author    = {Bordihn, Henning and Holzer, Markus and Kutrib, Martin},
  title     = {Unsolvability levels of operation problems for subclasses of context-free languages},
  issn      = {0129-0541},
  year      = {2005},
  abstract  = {We investigate the operation problem for linear and deterministic context-free languages: Fix an operation on formal languages. Given linear (deterministic, respectively) context-free languages, is the application of this operation to the given languages still a linear (deterministic, respectively) context-free language? Besides the classical operations, for which the linear and deterministic context-free languages are not closed, we also consider the recently introduced root and power operation. We show non-semidecidability, to be more precise, we show completeness for the second level of the arithmetic hierarchy for all of the aforementioned operations, except for the power operation, if the underlying alphabet contains at least two letters. The result for the power opera, tion solves an open problem stated in Theoret. Comput. Sci. 314 (2004) 445-449},
  language  = {en}
}
@article{Bordihn2004,
  author    = {Bordihn, Henning},
  title     = {Context-freeness of the power of context-free languages is undecidable},
  issn      = {0304-3975},
  year      = {2004},
  abstract  = {The power of a language L is the set of all powers of the words in L. In this paper, the following decision problem is investigated. Given a context-free language L, is the power of L context-free? We show that this problem is decidable for languages over unary alphabets, but it is undecidable whenever languages over alphabets with at least two letters are considered. (C) 2003 Elsevier B.V. All rights reserved},
  language  = {en}
}
@phdthesis{Bordihn2011,
  author    = {Bordihn, Henning},
  title     = {Contributions to the syntactical analysis beyond context-freeness},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-59719},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {Parsability approaches of several grammar formalisms generating also non-context-free languages are explored. Chomsky grammars, Lindenmayer systems, grammars with controlled derivations, and grammar systems are treated. Formal properties of these mechanisms are investigated, when they are used as language acceptors. Furthermore, cooperating distributed grammar systems are restricted so that efficient deterministic parsing without backtracking becomes possible. For this class of grammar systems, the parsing algorithm is presented and the feature of leftmost derivations is investigated in detail.},
  language  = {en}
}
@misc{BordihnNagyVaszil2018,
  author    = {Bordihn, Henning and Nagy, Benedek and Vaszil, Gy{\"o}rgy},
  title     = {Preface: Non-classical models of automata and applications VIII},
  series = {RAIRO-Theoretical informatics and appli and applications},
  volume    = {52},
  journal   = {RAIRO-Theoretical informatics and appli and applications},
  number    = {2-4},
  publisher = {EDP Sciences},
  address   = {Les Ulis},
  issn      = {0988-3754},
  doi       = {10.1051/ita/2018019},
  pages     = {87 -- 88},
  year      = {2018},
  language  = {en}
}
@article{BordihnVaszil2020,
  author    = {Bordihn, Henning and Vaszil, Gy{\"o}rgy},
  title     = {Deterministic Lindenmayer systems with dynamic control of parallelism},
  series = {International journal of foundations of computer science},
  volume    = {31},
  journal   = {International journal of foundations of computer science},
  number    = {1},
  publisher = {World Scientific},
  address   = {Singapore},
  issn      = {0129-0541},
  doi       = {10.1142/S0129054120400031},
  pages     = {37 -- 51},
  year      = {2020},
  abstract  = {M-rate 0L systems are interactionless Lindenmayer systems together with a function assigning to every string a set of multisets of productions that may be applied simultaneously to the string. Some questions that have been left open in the forerunner papers are examined, and the computational power of deterministic M-rate 0L systems is investigated, where also tabled and extended variants are taken into consideration.},
  language  = {en}
}
@article{BordihnVaszil2021,
  author    = {Bordihn, Henning and Vaszil, Gy{\"o}rgy},
  title     = {Reversible parallel communicating finite automata systems},
  series = {Acta informatica},
  volume    = {58},
  journal   = {Acta informatica},
  number    = {4},
  publisher = {Springer},
  address   = {Berlin ; Heidelberg ; New York, NY},
  issn      = {0001-5903},
  doi       = {10.1007/s00236-021-00396-9},
  pages     = {263 -- 279},
  year      = {2021},
  abstract  = {We study the concept of reversibility in connection with parallel communicating systems of finite automata (PCFA in short). We define the notion of reversibility in the case of PCFA (also covering the non-deterministic case) and discuss the relationship of the reversibility of the systems and the reversibility of its components. We show that a system can be reversible with non-reversible components, and the other way around, the reversibility of the components does not necessarily imply the reversibility of the system as a whole. We also investigate the computational power of deterministic centralized reversible PCFA. We show that these very simple types of PCFA (returning or non-returning) can recognize regular languages which cannot be accepted by reversible (deterministic) finite automata, and that they can even accept languages that are not context-free. We also separate the deterministic and non-deterministic variants in the case of systems with non-returning communication. We show that there are languages accepted by non-deterministic centralized PCFA, which cannot be recognized by any deterministic variant of the same type.},
  language  = {en}
}
@article{BordihnHolzer2021,
  author    = {Bordihn, Henning and Holzer, Markus},
  title     = {On the number of active states in finite automata},
  series = {Acta informatica},
  volume    = {58},
  journal   = {Acta informatica},
  number    = {4},
  publisher = {Springer},
  address   = {Berlin ; Heidelberg [u.a.]},
  issn      = {0001-5903},
  doi       = {10.1007/s00236-021-00397-8},
  pages     = {301 -- 318},
  year      = {2021},
  abstract  = {We introduce a new measure of descriptional complexity on finite automata, called the number of active states. Roughly speaking, the number of active states of an automaton A on input w counts the number of different states visited during the most economic computation of the automaton A for the word w. This concept generalizes to finite automata and regular languages in a straightforward way. We show that the number of active states of both finite automata and regular languages is computable, even with respect to nondeterministic finite automata. We further compare the number of active states to related measures for regular languages. In particular, we show incomparability to the radius of regular languages and that the difference between the number of active states and the total number of states needed in finite automata for a regular language can be of exponential order.},
  language  = {en}
}
@article{BordihnMitrana2020,
  author    = {Bordihn, Henning and Mitrana, Victor},
  title     = {On the degrees of non-regularity and non-context-freeness},
  series = {Journal of computer and system sciences},
  volume    = {108},
  journal   = {Journal of computer and system sciences},
  publisher = {Elsevier},
  address   = {San Diego, Calif. [u.a.]},
  issn      = {0022-0000},
  doi       = {10.1016/j.jcss.2019.09.003},
  pages     = {104 -- 117},
  year      = {2020},
  abstract  = {We study the derivational complexity of context-free and context-sensitive grammars by counting the maximal number of non-regular and non-context-free rules used in a derivation, respectively. The degree of non-regularity/non-context-freeness of a language is the minimum degree of non-regularity/non-context-freeness of context-free/context-sensitive grammars generating it. A language has finite degree of non-regularity iff it is regular. We give a condition for deciding whether the degree of non-regularity of a given unambiguous context-free grammar is finite. The problem becomes undecidable for arbitrary linear context-free grammars. The degree of non-regularity of unambiguous context-free grammars generating non-regular languages as well as that of grammars generating deterministic context-free languages that are not regular is of order Omega(n). Context-free non-regular languages of sublinear degree of non-regularity are presented. A language has finite degree of non-context-freeness if it is context-free. Context-sensitive grammars with a quadratic degree of non-context-freeness are more powerful than those of a linear degree.},
  language  = {en}
}