Abstract
The purpose of this paper is to investigate the computational complexities of deterministic multistack-tape automata and deterministic multipushdown-tape automata. It is shown that if a given computation requires T(n) steps for a k -tape Turing machine, then it requires at most rT(n) log 2 T(n) steps for a deterministic two-stack-tape automaton, where r is a constant independent of n . Hierarchies of computational complexity classes are examined; for instance, it is shown that for any pair of real numbers ( p, q ) satisfying the condition 1≤ p < q ≤2, the class of languages n p -recognizable by off-line deterministic two-pushdown-tape automata is properly contained in the class of languages n q -recognizable by off-line deterministic two-pushdown-tape automata. It is also shown that any context-free langauge is recognized by a deterministic three-pushdown-tape automaton in a number of steps proportional to the cube of the input length.
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