Modern programming languages use regular expressions to define valid tokens. Traditional lexical analyzers based on minimum deterministic finite automata for regular expressions cannot handle the look-ahead problem. The scanner writer needs to explicitly identify the look-ahead states and code the buffering and re-scanning operations by hand. We identify the class of finite look-ahead finite au...

We introduce quantum finite state transducers (qfst), and study the class of relations which they compute. It turns out that they share many features with probabilistic finite state transducers, especially regarding undecidability of emptiness (at least for low probability of success). However, like their ‘little brothers’, the quantum finite automata, the power of qfst is incomparable to that ...

Resource-bounded dimension is a notion of computational information density of infinite sequences based on computationally bounded gamblers. This paper develops the theory of pushdown dimension and explores its relationship with finite-state dimension. The pushdown dimension of any sequence is trivially bounded above by its finite-state dimension, since a pushdown gambler can simulate any finit...

We present a few results and several open problems concerning complete deterministic finite automata in which every non-empty subset of the state set occurs as the image of the whole state set under the action of a suitable input word.

Active language learning is an interesting task for which theoretical results are known and several applications exist. In order to better understand what the better strategies may be, a new competition called Zulu (http://labh-curien.univ-st-etienne.fr/zulu/) is launched: participants are invited to learn deterministic finite automata from membership queries. The goal is to obtain the best cla...

We examine questions involving nondeterministic finite automata where all states are final, initial, or both initial and final. First, we prove hardness results for the nonuniversality and inequivalence problems for these NFAs. Next, we characterize the languages accepted. Finally, we discuss some state complexity problems involving such automata.

in this paper, our focus of attention is the proper propagationof fuzzy degrees in determinization of $nondeterministic$ $fuzzy$$finite$ $tree$ $automata$ (nffta). initially, two determinizationmethods are introduced which have some limitations (one inbehavior preserving and other in type of fuzzy operations). inorder to eliminate these limitations and increasing theefficiency of ffta, we defin...

In the theory of automata the question about difference between the size of deterministic and nondeterministic automata which recognize the same language is of great importance. However, this problem has been studied mainly in case when input alphabet consists of at least 2 letters. In this paper some special kind of languages in one letter alphabet will be discussed and the estimate of the num...

NFA usually requires significantly less states than DFA to recognize the same language. NFAs in one letter input alphabet are more restricted and the gap between NFAs and DFAs decreases, because the power of NFA is in its ability to reach many subsets of its state set. We discuss limitations of DFAs in one letter input alphabet and show that approximately 1/4 of all subsets are unreachable and ...

We study structural restrictions on biautomata such as, e.g., acyclicity, permutation-freeness, strongly permutation-freeness, and orderability, to mention a few. We compare the obtained language families with those induced by deterministic finite automata with the same property. In some cases, it is shown that there is no difference in characterization between deterministic finite automata and...