On pebble automata

Tree-Walking Pebble Automata

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...

A Note on Two-pebble Automata Over Infinite Alphabets

It is shown that the emptiness problem for 2-pebble automata languages is undecidable and that 2-pebble automata are weaker than 3-pebble automata.

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.

On Pebble Automata for Data Languages with Decidable Emptiness Problem

In this paper we study a subclass of pebble automata (PA) for data languages for which the emptiness problem is decidable. Namely, we show that the emptiness problem for weak 2-pebble automata is decidable, while the same problem for weak 3-pebble automata is undecidable. We also introduce the so-called top view weak PA. Roughly speaking, top view weak PA are weak PA where the equality test is ...