On multi-head automata with restricted nondeterminism

In this work, we consider deterministic two-way multi-head automata, the input heads of which are nondeterministically initialised, i.e., in every computation each input head is initially located at some nondeterministically chosen position of the input word. This model serves as an instrument to investigate restricted nondeterminism of two-way multi-head automata. Our result is that, in terms of expressive power, two-way multi-head automata with nondeterminism in form of nondeterministically initialising the input heads or with restricted nondeterminism in the classical way, i.e., in every accepting computation the number of nondeterministic steps is bounded by a constant, do not yield an advantage over their completely deterministic counter-parts with the same number of input heads. We conclude this paper with a brief application of this result.

► Two variants of multi-head automata with restricted nondeterminism are considered. ► Both models turn out to be of identical computational power. ► Both models are shown to coincide with deterministic multi-head automata.