Buffered Simulation Games for B\"uchi Automata

Simulation relations are an important tool in automata theory because they provide efficiently computable approximations to language inclusion. In recent years, extensions of ordinary simulations have been studied, for instance multi-pebble and multi-letter simulations which yield better approximations and are still polynomial-time computable. In this paper we study the limitations of approximating language inclusion in this way: we introduce a natural extension of multi-letter simulations called buffered simulations. They are based on a simulation game in which the two players share a FIFO buffer of unbounded size. We consider two variants of these buffered games called continuous and look-ahead simulation which differ in how elements can be removed from the FIFO buffer. We show that look-ahead simulation, the simpler one, is already PSPACE-hard, i.e. computationally as hard as language inclusion itself. Continuous simulation is even EXPTIME-hard. We also provide matching upper bounds for solving these games with infinite state spaces.Comment: In Proceedings AFL 2014, arXiv:1405.527

Searching for insubordination: An analysis of ləbo in Lamaholot

In this paper, we present a description and analysis of ləbo ‘although’ in Lamaholot of eastern Indonesia, which is a subordinating conjunction that expresses a concessive relation between main and subordinate clauses. Although clause-initial conjunctions are predominant in this SVO language, the conjunction ləbo appears in clause-final position. Interestingly, subordinate clauses headed by ləbo can stand alone without a main clause, conveying the speaker’s irritation or blame toward the hearer or an undesirable event. By providing synchronic evidence of different kinds, this paper proposes that this construction involves insubordination, the independent use of constructions exhibiting prima facie characteristics of subordinate clauses (Evans 2007)

Graph Concatenation for Quantum Codes

Graphs are closely related to quantum error-correcting codes: every stabilizer code is locally equivalent to a graph code, and every codeword stabilized code can be described by a graph and a classical code. For the construction of good quantum codes of relatively large block length, concatenated quantum codes and their generalizations play an important role. We develop a systematic method for constructing concatenated quantum codes based on "graph concatenation", where graphs representing the inner and outer codes are concatenated via a simple graph operation called "generalized local complementation." Our method applies to both binary and non-binary concatenated quantum codes as well as their generalizations.Comment: 26 pages, 12 figures. Figures of concatenated [[5,1,3]] and [[7,1,3]] are added. Submitted to JM

History-Register Automata

Programs with dynamic allocation are able to create and use an unbounded number of fresh resources, such as references, objects, files, etc. We propose History-Register Automata (HRA), a new automata-theoretic formalism for modelling such programs. HRAs extend the expressiveness of previous approaches and bring us to the limits of decidability for reachability checks. The distinctive feature of our machines is their use of unbounded memory sets (histories) where input symbols can be selectively stored and compared with symbols to follow. In addition, stored symbols can be consumed or deleted by reset. We show that the combination of consumption and reset capabilities renders the automata powerful enough to imitate counter machines, and yields closure under all regular operations apart from complementation. We moreover examine weaker notions of HRAs which strike different balances between expressiveness and effectiveness.Comment: LMCS (improved version of FoSSaCS

A Schur function identity related to the (-1)-enumeration of self-complementary plane partitions

We give another proof for the (-1)-enumeration of self-complementary plane partitions with at least one odd side-length by specializing a certain Schur function identity. The proof is analogous to Stanley's proof for the ordinary enumeration. In addition, we obtain enumerations of 180-degree symmetric rhombus tilings of hexagons with a barrier of arbitrary length along the central line.Comment: AMSLatex, 14 pages, Parity conditions in Theorem 3 corrected and an additional case adde

Inferentials in spoken English

Although there is a growing body of research on inferential sentences (Declerck 1992, Delahunty 1990, 1995, 2001, Koops 2007, Pusch 2006), most of this research has been on their forms and functions in written discourse. This has left a gap with regards to their range of structural properties and allowed disagreement over their analysis to linger without a conclusive resolution. Most accounts regard the inferential as a type of it-cleft (Declerck 1992, Delahunty 2001, Huddleston and Pullum 2002, Lambrecht 2001), while a few view it as an instance of extraposition (Collins 1991, Schmid 2009). More recently, Pusch's work in Romance languages proposes the inferential is used as a discourse marker (2006, forthcoming). Based on a corpus study of examples from spoken New Zealand English, the current paper provides a detailed analysis of the formal and discoursal properties of several sub-types of inferentials (positive, negative, as if and like inferentials). We show that despite their apparent formal differences from the prototypical cleft, inferentials are nevertheless best analysed as a type of cleft, though this requires a minor reinterpretation of “cleft construction.” We show how similar the contextualized interpretations of clefts and inferentials are and how these are a function of their lexis and syntax

The Isomorphism Relation Between Tree-Automatic Structures

An $\omega$-tree-automatic structure is a relational structure whose domain and relations are accepted by Muller or Rabin tree automata. We investigate in this paper the isomorphism problem for $\omega$-tree-automatic structures. We prove first that the isomorphism relation for $\omega$-tree-automatic boolean algebras (respectively, partial orders, rings, commutative rings, non commutative rings, non commutative groups, nilpotent groups of class n >1) is not determined by the axiomatic system ZFC. Then we prove that the isomorphism problem for $\omega$-tree-automatic boolean algebras (respectively, partial orders, rings, commutative rings, non commutative rings, non commutative groups, nilpotent groups of class n >1) is neither a $\Sigma_2^1$-set nor a $\Pi_2^1$-set