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How Hard Is Finding Shortest Counter-Example Lassos in Model Checking?

  • Rüdiger EhlersEmail author
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 11800)

Abstract

Modern model checkers help system engineers to pinpoint the reason for the faulty behavior of a system by providing counter-example traces. For finite-state systems and \(\omega \)-regular specifications, they come in the form of lassos. Lassos that are unnecessarily long should be avoided, as they make finding the cause for an error in a trace harder.

We give the first thorough characterization of the computational complexity of finding the shortest and approximately shortest counter-example lassos in model checking for the full class of \(\omega \)-regular specifications. We show how to build (potentially exponentially larger) tight automata for arbitrary \(\omega \)-regular specifications, which can be used to reduce finding shortest counter-example lassos for some finite-state system to finding a shortest accepting lasso in a (product) Büchi automaton. We then show that even approximating the size of the shortest counter-example lasso is an NP-hard problem for any polynomial approximation function, which demonstrates the hardness of obtaining short counter-examples in practical model checking. Minimizing only the length of the lasso cycle is however possible in polynomial time for a fixed but arbitrary upper limit on the size of strongly connected components in specification automata.

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Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  1. 1.Clausthal University of TechnologyClausthal-ZellerfeldGermany

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