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arXiv math/9907044math.LO
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只有一条磁带的无限时间图灵机

Infinite time Turing machines with only one tape

Joel David Hamkins, Daniel Evan Seabold

摘要:

只有一个磁带的无限时间图灵机在许多方面与它们的多磁带表兄弟一样强大。特别是,这两种机器模型产生了相同类别的可判定集,相同的度结构,至少对于函数f:R->N,相同类别的可计算函数。然而,存在无限时间可计算函数f:R-->R,它们不是单磁带可计算的,因此这两种超任务计算模型是不等价的。令人惊讶的是,单带可计算函数的类在复合下不是封闭的;但是在复合下封闭它会产生所有无限时间可计算函数的完整类。最后,每个可被无限时间图灵机时钟化的序数也可被单带机时钟化,除了某些孤立的序数,它们结束了可时钟化序数中的间隔。

英文摘要:

Infinite time Turing machines with only one tape are in many respects fully as powerful as their multi-tape cousins. In particular, the two models of machine give rise to the same class of decidable sets, the same degree structure and, at least for functions f:R-->N, the same class of computable functions. Nevertheless, there are infinite time computable functions f:R-->R that are not one-tape computable, and so the two models of supertask computation are not equivalent. Surprisingly, the class of one-tape computable functions is not closed under composition; but closing it under composition yields the full class of all infinite time computable functions. Finally, every ordinal which is clockable by an infinite time Turing machine is clockable by a one-tape machine, except certain isolated ordinals that end gaps in the clockable ordinals.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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