Strategy Complexity of Parity Objectives in Countable MDPs

Authors Stefan Kiefer, Richard Mayr, Mahsa Shirmohammadi, Patrick Totzke

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Author Details

Stefan Kiefer
  • Department of Computer Science, University of Oxford, UK
Richard Mayr
  • School of Informatics, University of Edinburgh, UK
Mahsa Shirmohammadi
  • CNRS & IRIF, Université de Paris, FR
Patrick Totzke
  • Department of Computer Science, University of Liverpool, UK

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Stefan Kiefer, Richard Mayr, Mahsa Shirmohammadi, and Patrick Totzke. Strategy Complexity of Parity Objectives in Countable MDPs. In 31st International Conference on Concurrency Theory (CONCUR 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 171, pp. 39:1-39:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)


We study countably infinite MDPs with parity objectives. Unlike in finite MDPs, optimal strategies need not exist, and may require infinite memory if they do. We provide a complete picture of the exact strategy complexity of ε-optimal strategies (and optimal strategies, where they exist) for all subclasses of parity objectives in the Mostowski hierarchy. Either MD-strategies, Markov strategies, or 1-bit Markov strategies are necessary and sufficient, depending on the number of colors, the branching degree of the MDP, and whether one considers ε-optimal or optimal strategies. In particular, 1-bit Markov strategies are necessary and sufficient for ε-optimal (resp. optimal) strategies for general parity objectives.

Subject Classification

ACM Subject Classification
  • Theory of computation → Random walks and Markov chains
  • Mathematics of computing → Probability and statistics
  • Markov decision processes
  • Parity objectives
  • Levy’s zero-one law


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