15 research outputs found
Tabular Parsing
This is a tutorial on tabular parsing, on the basis of tabulation of
nondeterministic push-down automata. Discussed are Earley's algorithm, the
Cocke-Kasami-Younger algorithm, tabular LR parsing, the construction of parse
trees, and further issues.Comment: 21 pages, 14 figure
Generalizations of the Muller-Schupp theorem and tree-like inverse graphs
We extend the characterization of context-free groups of Muller and Schupp in
two ways. We first show that for a quasi-transitive inverse graph ,
being quasi-isometric to a tree, or context-free (finitely many end-cones
types), or having the automorphism group that is virtually free,
are all equivalent conditions. Furthermore, we add to the previous equivalences
a group theoretic analog to the representation theorem of
Chomsky-Sch\"utzenberger that is fundamental in solving a weaker version of a
conjecture of T. Brough which also extends Muller and Schupp' result to the
class of groups that are virtually finitely generated subgroups of direct
product of free groups. We show that such groups are precisely those whose word
problem is the intersection of a finite number of languages accepted by
quasi-transitive, tree-like inverse graphs
Reversible Two-Party Computations
Deterministic synchronous systems consisting of two finite automata running
in opposite directions on a shared read-only input are studied with respect to
their ability to perform reversible computations, which means that the automata
are also backward deterministic and, thus, are able to uniquely step the
computation back and forth. We study the computational capacity of such devices
and obtain on the one hand that there are regular languages that cannot be
accepted by such systems. On the other hand, such systems can accept even
non-semilinear languages. Since the systems communicate by sending messages, we
consider also systems where the number of messages sent during a computation is
restricted. We obtain a finite hierarchy with respect to the allowed amount of
communication inside the reversible classes and separations to general, not
necessarily reversible, classes. Finally, we study closure properties and
decidability questions and obtain that the questions of emptiness, finiteness,
inclusion, and equivalence are not semidecidable if a superlogarithmic amount
of communication is allowed.Comment: In Proceedings AFL 2023, arXiv:2309.0112
Reversible Computation: Extending Horizons of Computing
This open access State-of-the-Art Survey presents the main recent scientific outcomes in the area of reversible computation, focusing on those that have emerged during COST Action IC1405 "Reversible Computation - Extending Horizons of Computing", a European research network that operated from May 2015 to April 2019. Reversible computation is a new paradigm that extends the traditional forwards-only mode of computation with the ability to execute in reverse, so that computation can run backwards as easily and naturally as forwards. It aims to deliver novel computing devices and software, and to enhance existing systems by equipping them with reversibility. There are many potential applications of reversible computation, including languages and software tools for reliable and recovery-oriented distributed systems and revolutionary reversible logic gates and circuits, but they can only be realized and have lasting effect if conceptual and firm theoretical foundations are established first
Reversible Computation: Extending Horizons of Computing
This open access State-of-the-Art Survey presents the main recent scientific outcomes in the area of reversible computation, focusing on those that have emerged during COST Action IC1405 "Reversible Computation - Extending Horizons of Computing", a European research network that operated from May 2015 to April 2019. Reversible computation is a new paradigm that extends the traditional forwards-only mode of computation with the ability to execute in reverse, so that computation can run backwards as easily and naturally as forwards. It aims to deliver novel computing devices and software, and to enhance existing systems by equipping them with reversibility. There are many potential applications of reversible computation, including languages and software tools for reliable and recovery-oriented distributed systems and revolutionary reversible logic gates and circuits, but they can only be realized and have lasting effect if conceptual and firm theoretical foundations are established first