PSPACE-Completeness of Reversible Deterministic Systems.

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Bibliographic Details
Title: PSPACE-Completeness of Reversible Deterministic Systems.
Authors: Demaine, Erik D.1 (AUTHOR) edemaine@mit.edu, Hearn, Robert A.1 (AUTHOR) bob@hearn.to, Hendrickson, Dylan1 (AUTHOR) dylanhen@mit.edu, Lynch, Jayson1 (AUTHOR) jaysonl@mit.edu
Source: International Journal of Foundations of Computer Science. Nov2025, Vol. 36 Issue 7, p1041-1062. 22p.
Subjects: Reversible computing, Computational complexity, Deterministic algorithms, Planning techniques, Constraint programming
Abstract: We prove PSPACE-completeness of several reversible, fully deterministic systems. At the core, we develop a framework for such proofs (building on a result of Tsukiji and Hagiwara and a framework for motion planning through gadgets), showing that any system that can implement three basic gadgets is PSPACE-complete. We then apply this framework to four different systems, showing its versatility. First, we prove that Deterministic Constraint Logic is PSPACE-complete, fixing an error in a previous argument from 2008. Second, we give a new PSPACE-hardness proof for the reversible 'billiard ball' model of Fredkin and Toffoli from 40 years ago, newly establishing hardness when only two balls move at once. Third, we prove PSPACE-completeness of zero-player motion planning with any reversible deterministic interacting k-tunnel gadget and a 'rotate clockwise' gadget (a zero-player analog of branching hallways). Fourth, we give simpler proofs that zero-player motion planning is PSPACE-complete with just a single gadget, the 3-spinner. These results should in turn make it even easier to prove PSPACE-hardness of other reversible deterministic systems. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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