Quasipolynomial Computation of Nested Fixpoints

Hausmann D, Schröder L (2021)

Publication Language: English

Publication Type: Conference contribution

Publication year: 2021

Journal

Lecture Notes in Computer Science Springer Verlag

Publisher: Springer

Series: Lecture Notes in Computer Science

City/Town: Cham

Book Volume: 12651

Pages Range: 38-56

Conference Proceedings Title: Tools and Algorithms for the Construction and Analysis of Systems. 27th International Conference, TACAS 2021, Held as Part of the European Joint Conferences on Theory and Practice of Software, ETAPS 2021, Luxembourg City, Luxembourg, March 27 – April 1, 2021, Proceedings, Part I

Event location: Virtual, Online LU

ISBN: 9783030720155

DOI: 10.1007/978-3-030-72016-2_3

Abstract

It is well-known that the winning region of a parity game with n nodes and k priorities can be computed as a k-nested fixpoint of a suitable function; straightforward computation of this nested fixpoint requires O(nk2 ) iterations of the function. Calude et al.’s recent quasipolynomial-time parity game solving algorithm essentially shows how to compute the same fixpoint in only quasipolynomially many iterations by reducing parity games to quasipolynomially sized safety games. Universal graphs have been used to modularize this transformation of parity games to equivalent safety games that are obtained by combining the original game with a universal graph. We show that this approach naturally generalizes to the computation of solutions of systems of any fixpoint equations over finite lattices; hence, the solution of fixpoint equation systems can be computed by quasipolynomially many iterations of the equations. We present applications to modal fixpoint logics and games beyond relational semantics. For instance, the model checking problems for the energy μ-calculus, finite latticed μ-calculi, and the graded and the (two-valued) probabilistic μ-calculus – with numbers coded in binary – can be solved via nested fixpoints of functions that differ substantially from the function for parity games but still can be computed in quasipolynomial time; our result hence implies that model checking for these μ-calculi is in QP. Moreover, we improve the exponent in known exponential bounds on satisfiability checking.

Authors with CRIS profile

Daniel Hausmann Lehrstuhl für Informatik 8 (Theoretische Informatik) Lutz Schröder Lehrstuhl für Informatik 8 (Theoretische Informatik)

How to cite

APA:

Hausmann, D., & Schröder, L. (2021). Quasipolynomial Computation of Nested Fixpoints. In Jan Friso Groote, Kim Guldstrand Larsen (Eds.), Tools and Algorithms for the Construction and Analysis of Systems. 27th International Conference, TACAS 2021, Held as Part of the European Joint Conferences on Theory and Practice of Software, ETAPS 2021, Luxembourg City, Luxembourg, March 27 – April 1, 2021, Proceedings, Part I (pp. 38-56). Virtual, Online, LU: Cham: Springer.

MLA:

Hausmann, Daniel, and Lutz Schröder. "Quasipolynomial Computation of Nested Fixpoints." Proceedings of the 27th International Conference on Tools and Algorithms for the Construction and Analysis of Systems, TACAS 2021 Held as Part of 24th European Joint Conferences on Theory and Practice of Software, ETAPS 2021, Virtual, Online Ed. Jan Friso Groote, Kim Guldstrand Larsen, Cham: Springer, 2021. 38-56.

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