Pebble Alternating Tree-Walking Automata and Their Recognizing Power

Expressive Power of Pebble Automata

Two variants of pebble tree-walking automata on trees are considered that were introduced in the literature. It is shown that for each number of pebbles, the two models have the same expressive power both in the deterministic case and in the nondeterministic case. Furthermore, nondeterministic (resp. deterministic) treewalking automata with n+ 1 pebbles can recognize more languages than those w...

Determinizing Two-way Alternating Pebble Automata for Data Languages

We prove that for every integer k ≥ 1, two-way alternating kpebble automata and one-way deterministic k-pebble automata for data languages have the same recognition power.

Tree-Walking Pebble Automata

Alternating Regular Tree Grammars in the Framework of Lattice-Valued Logic

In this paper, two different ways of introducing alternation for lattice-valued (referred to as {L}valued)  regular tree grammars and {L}valued top-down tree automata are compared. One is the way which defines the alternating regular tree grammar, i.e., alternation is governed by the non-terminals of the grammar and the other is the way which combines state with alternation. The first way is ta...

Complexity of Pebble Tree-Walking Automata

We consider tree-walking automata using k pebbles. The pebbles are either strong (can be lifted from anywhere) or weak (can be lifted only when the automaton is on it). For each k, we give the precise complexities of the problems of emptiness and inclusion of tree-walking automata using k pebbles.