We consider the problem of finding all subtree repeats in a given unranked ordered tree. We show a new, elegant, and simple method, which is based on the construction of a tree indexing structure called the subtree pushdown automaton. We propose a solution for computing all subtree repeats from the deterministic subtree pushdown automaton constructed over the subject tree. The method we present...

We consider way k tape alternating pushdown automata k apa and way k tape alternating nite automata k afa We say that an alternating automaton accepts a language L with f n bounded maximal respectively minimal leaf size if arbitrary re spectively at least one accepting tree for any w L has no more than f jwj leaves The main results of the article are the following For way k tape alternating cou...

The state-alternating context-free grammars are introduced, and the language classes obtained from them are compared to the classes of the Chomsky hierarchy as well as to some well-known complexity classes. In particular, the state-alternating context-free grammars are compared to the alternating context-free grammars of Moriya (1989) and to the alternating pushdown automata. Further, various d...

In this paper we develop an automata-theoretic framework for reasoning about infinite-state sequential systems. 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. Checking that a system satisfies a tem...

We introduce and investigate stack transducers, which are one-way stack automata with an output tape. A one-way stack automaton is a classical pushdown automaton with the additional ability to move the stack head inside the stack without altering the contents. For stack transducers, we distinguish between a digging and a non-digging mode. In digging mode, the stack transducer can write on the o...

We define the class of micro-macro stack graphs, a new class of graphs modeling infinite-state sequential systems with a decidable model-checking problem. Micro-macro stack graphs are the configuration graphs of stack automata whose states are partitioned into micro and macro states. Nodes of the graph are configurations of the stack automaton where the state is a macro state. Edges of the grap...

In recent work, Kobayashi observed that the acceptance by an alternating tree automaton A of an infinite tree T generated by a higher-order recursion scheme G may be formulated as the typability of the recursion scheme G in an appropriate intersection type system associated to the automaton A . The purpose of this article is to establish a clean connection between this line of work and Bucciare...

String suffix automata accept all suffixes of a given string and belong to the fundamental stringology principles. Extending their transitions by specific pushdown operations results in new subtree pushdown automata, which accept all subtrees of a given subject tree in prefix notation and are analogous to the suffix automata in their properties. The deterministic subtree pushdown automaton acce...

We give a general approach to show the closure under complement and decide the emptiness for many classes of multistack visibly pushdown automata (Mvpa). A central notion in our approach is the visibly path-tree, i.e., a stack tree with the encoding of a path that denotes a linear ordering of the nodes. We show that the set of all such trees with a bounded size labeling is regular, and path-tre...

An automaton is universal if it accepts every possible input. We study the notion of u-universality, which asserts that the automaton accepts every input starting with u. Universality and u-universality are both EXPTIME-hard for non-deterministic tree automata. We propose efficient antichain-based techniques to address these problems for visibly pushdown automata operating on trees. One of our ...