A non-deterministic automaton running on infinite trees is unambiguous if it has at most one accepting run on every tree. The class of languages recognisable by unambiguous tree automata is still not well-understood. In particular, decidability of the problem whether a given language is recognisable by some unambiguous automaton is open. Moreover, there are no known upper bounds on the descript...

A non-deterministic automaton running on infinite trees is unambiguous if it has at most one accepting run on every tree. The class of languages recognisable by unambiguous tree automata is still not well-understood. In particular, decidability of the problem whether a given language is recognisable by some unambiguous automaton is open. Moreover, there are no known upper bounds on the descript...

We extend the automata-theoretic framework for reasoning about infinitestate sequential systems to handle also the global model-checking problem. Our framework is based on the observation that states of such systems, which carry a finite but unbounded amount of information, can be viewed as nodes in an infinite tree, and transitions between states can be simulated by finite-state automata. Chec...

We consider the emptiness problem for alternating tree automata, with two acceptance semantics: classical (all branches are accepted) and qualitative (almost all branches are accepted). For the classical semantics, the usual technique to tackle this problem relies on a Simulation Theorem which constructs an equivalent non-deterministic automaton from the original alternating one, and then check...

We consider co–Büchi tree automata along with both alternating and generalized paradigms, as a characterization of the class of languages whose complement is accepted by generalized Büchi tree automata. We first prove that for alternating generalized co–Büchi tree automata the simulation theorem does not hold and the generalized acceptance does not add to the expressive power of the model. Then...

Many aspects of machine translation of natural languages can be formalized by employing weighted finite-state (string) transducers [22, 40]. Successful implementations based on this wordor phrasebased approach are, for example, the At&t Fsm toolkit [41], Xerox’s finite-state calculus [24], the Rwth toolkit [23], Carmel [19], and OpenFst [2]. However, the phrase-based approach is not expressive ...

Article history: Received 23 December 2009 Received in revised form 3 April 2013 Available online 18 April 2014

The field of finite tree automata provides fundamental notations and tools for reasoning about set of terms called regular or recognizable tree languages. We consider two kinds of analysis using regular tree languages, applied to logic programs. The first approach is to try to discover automatically a tree automaton from a logic program, approximating its minimal Herbrand model. In this case th...

Weakly definable languages of infinite trees are an expressive subclass of regular tree languages definable in terms of weak monadic second-order logic, or equivalently weak alternating automata. Our main result is that given a Büchi automaton, it is decidable whether the language is weakly definable. We also show that given a parity automaton, it is decidable whether the language is recognizab...