Hartmut Messerschmidt

On Stateless Two-Pushdown Automata and Restarting Automata

Restarting automata and two-pushdown automata are investigated that have a single internal state only. As such an automaton must always stay in the same state, this state is of no importance for the behaviour of the automaton. Accordingly, these automata are called stateless. We consider various types of stateless two-pushdown automata and restarting automata. We investigate their expressive power, comparing them in particular to each other and to the corresponding types of automata with states.

Cooperating Distributed Systems of Restarting Automata

Here we introduce cooperating distributed systems of restarting automata and establish that in mode = 1 they correspond to the non-forgetting restarting automaton.

On Deterministic CD-Systems of Restarting Automata

Three variants of determinism are introduced for CD-systems of restarting automata, called strict determinism, global determinism, and local determinism. In mode = 1 globally deterministic CD-systems of restarting automata are of the same expressive power as nonforgetting deterministic restarting automata of the same type, which corresponds to the situation for nondeterministic CD-systems. On the other hand, for the various types of restarting automata without auxiliary symbols, strictly deterministic CD-systems of restarting automata are strictly less expressive than the corresponding deterministic types of nonforgetting restarting automata. Further, globally deterministic CD-systems of restarting automata can be simulated by locally deterministic CD-systems of restarting automata of the same type. In fact, we conjecture that, for all types of restarting automata without auxiliary symbols, the latter are strictly more expressive than the former, but they are strictly less expressive than the corresponding nondeterministic CD-systems of restarting automata.

On nonforgetting restarting automata that are deterministic and/or monotone

The nonforgetting restarting automaton is a restarting automaton that is not forced to reset its internal state to the initial state when executing a restart operation. We analyse the expressive power of the various deterministic and/or monotone variants of this model.

Strictly deterministic CD-systems of restarting automata

A CD-system of restarting automata is called strictly deterministic if all its component systems are deterministic, and if there is a unique successor system for each component. Here we show that the strictly deterministic CD-systems of restarting automata are strictly more powerful than the corresponding deterministic types of restarting automata, but that they are strictly less powerful than the corresponding deterministic types of nonforgetting restarting automata. In fact, we present an infinite hierarchy of language classes based on the number of components of strictly deterministic CD-systems of restarting automata.

A Hierarchy of Monotone Deterministic Non-Forgetting Restarting Automata

AbstractThe non-forgetting restarting automaton is an extension of the restarting automaton that is obtained by combining the restart operation with a change of the internal state just like the other operations. Thus, when executing a restart operation a non-forgetting restarting automaton is not forced to reset its internal state to its initial state. We analyze the expressive power of the deterministic variants of this model. As our main result we establish a hierarchy of language classes that are characterized by various types of monotone deterministic non-forgetting restarting automata. This hierarchy ranges from the deterministic context-free languages to the so-called left-to-right regular languages. In particular, we show that for monotone deterministic non-forgetting restarting automata, the

On Stateless Deterministic Restarting Automata

\textsf{RRWW}

Correctness preservation and complexity of simple RL-automata

-model is strictly more powerful than the

Combining Conditional Random Fields and Background Knowledge for Improved Cyber Security

\textsf{RWW}

Strongly solving fox-and-geese on multi-core CPU

-model. This is the first time that for a particular type of restarting automaton the expressive power of the