Unambiguous Catalytic Computation

Authors Chetan Gupta, Rahul Jain , Vimal Raj Sharma, Raghunath Tewari

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Author Details

Chetan Gupta
  • Indian Institute of Technology Kanpur, India
Rahul Jain
  • Indian Institute of Technology Kanpur, India
Vimal Raj Sharma
  • Indian Institute of Technology Kanpur, India
Raghunath Tewari
  • Indian Institute of Technology Kanpur, India


The fourth author would like to thank Michal Koucký for valuable discussions and for suggesting key ideas which led to the proof of the main result in this paper. The first and third author would like to thank Ministry of Electronics and IT, India for supporting this research through the Visvesvaraya PhD. The authors would also like to thank the anonymous reviewers for their valuable comments which helped in improving the presentation of this paper and suggesting an alternative proof of CNL = coCNL as a corollary of our result.

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Chetan Gupta, Rahul Jain, Vimal Raj Sharma, and Raghunath Tewari. Unambiguous Catalytic Computation. In 39th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 150, pp. 16:1-16:13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)


The catalytic Turing machine is a model of computation defined by Buhrman, Cleve, Koucký, Loff, and Speelman (STOC 2014). Compared to the classical space-bounded Turing machine, this model has an extra space which is filled with arbitrary content in addition to the clean space. In such a model we study if this additional filled space can be used to increase the power of computation or not, with the condition that the initial content of this extra filled space must be restored at the end of the computation. In this paper, we define the notion of unambiguous catalytic Turing machine and prove that under a standard derandomization assumption, the class of problems solved by an unambiguous catalytic Turing machine is same as the class of problems solved by a general nondeterministic catalytic Turing machine in the logspace setting.

Subject Classification

ACM Subject Classification
  • Mathematics of computing
  • Catalytic computation
  • Logspace
  • Reinhardt-Allender


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