We introduce the concept of one-time nondeterminism as a new kind of limited nondeterminism for finite state machines and pushdown automata. Roughly speaking, one-time nondeterminism means that at the outset the computation is nondeterministic, but whenever it performs a guess, this guess is fixed for the rest of the computation. We characterize the computational power of one-time nondeterministic finite automata (OTNFAs) and one-time nondeterministic pushdown devices. Moreover, we study the descriptional complexity of these machines. For instance, we show that for an [Formula: see text]-state OTNFA with a sole nondeterministic state, that is nondeterministic for only one input symbol, [Formula: see text] states are sufficient and necessary in the worst case for an equivalent deterministic finite automaton. In case of pushdown automata, the conversion of a nondeterministic to a one-time nondeterministic as well as the conversion of a one-time nondeterministic to a deterministic one turn out to be non-recursive, that is, the trade-offs in size cannot be bounded by any recursive function.

中文翻译：

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一次性非确定性计算

我们引入一次性非确定性的概念作为有限状态机和下推自动机的一种新的有限非确定性。粗略地说，一次性不确定性意味着一开始计算是不确定的，但是每当它执行猜测时，这个猜测对于其余的计算都是固定的。我们描述了一次性非确定性有限自动机 (OTNFA) 和一次性非确定性下推设备的计算能力。此外，我们研究了这些机器的描述复杂性。例如，我们证明对于具有唯一不确定状态的 [公式：参见文本] 状态 OTNFA，即仅对一个输入符号是不确定的，[公式：参见文本] 状态在最坏情况下对于等价的是充分和必要的确定性有限自动机。在下推自动机的情况下，