A linear translation from LTL to the first-order modal µ-calculus

The modal µ-calculus is a very expressive temporal logic. In particular, logics such as LTL, CTL and CTL* can be translated into the modal mu-calculus, although existing translations of LTL and CTL* are at least exponential in size. We show that an existing simple first-order extension of the modal µ-calculus allows for a linear translation from LTL. Furthermore, we show that solving the translated formulae is as efficient as the best known methods to solve LTL formulae directly

Abstraction in parameterised Boolean equation systems

We present a general theory of abstraction for a variety of verification problems. Our theory is set in the framework of parameterized Boolean equation systems. The power of our abstraction theory is compared to that of generalised Kripke modal transition systems (GTSs). We show that for model checking the modal µ-calculus, our abstractions can be exponentially more succinct than GTSs and our theory is as complete as the GTS framework for abstraction. Furthermore, we investigate the completeness of our theory for verification problems other than the modal µ-calculus. We illustrate the potential of our theory through case studies using the first-order modal µ-calculus and a real-time extension thereof, conducted using a prototype implementation of a new syntactic transformation for equation systems

Model Checking the FlexRay Startup Phase

This report describes a discrete-time model of the startup phase of a FlexRay network. The startup behaviour of this network is analysed in the presence of several faults. It is shown that in certain cases a faulty node can prevent the network from communicating altogether. One previously unknown scenario is uncovered

Oink: an Implementation and Evaluation of Modern Parity Game Solvers

Parity games have important practical applications in formal verification and synthesis, especially to solve the model-checking problem of the modal mu-calculus. They are also interesting from the theory perspective, as they are widely believed to admit a polynomial solution, but so far no such algorithm is known. In recent years, a number of new algorithms and improvements to existing algorithms have been proposed. We implement a new and easy to extend tool Oink, which is a high-performance implementation of modern parity game algorithms. We further present a comprehensive empirical evaluation of modern parity game algorithms and solvers, both on real world benchmarks and randomly generated games. Our experiments show that our new tool Oink outperforms the current state-of-the-art.Comment: Accepted at TACAS 201

An O(mlog⁡n)O(m\log n) Algorithm for Stuttering Equivalence and Branching Bisimulation

We provide a new algorithm to determine stuttering equivalence with time complexity $O(m \log n)$, where $n$ is the number of states and $m$ is the number of transitions of a Kripke structure. This algorithm can also be used to determine branching bisimulation in $O(m(\log |\mathit{Act}|+ \log n))$ time where $\mathit{Act}$ is the set of actions in a labelled transition system. Theoretically, our algorithm substantially improves upon existing algorithms which all have time complexity $O(m n)$ at best. Moreover, it has better or equal space complexity. Practical results confirm these findings showing that our algorithm can outperform existing algorithms with orders of magnitude, especially when the sizes of the Kripke structures are large. The importance of our algorithm stretches far beyond stuttering equivalence and branching bisimulation. The known $O(m n)$ algorithms were already far more efficient (both in space and time) than most other algorithms to determine behavioural equivalences (including weak bisimulation) and therefore it was often used as an essential preprocessing step. This new algorithm makes this use of stuttering equivalence and branching bisimulation even more attractive.Comment: A shortened version of this technical report has been published in the proceedings of TACAS 201

Assessing dysphagia via telerehabilitation: patient perceptions and satisfaction

To gain insight into factors which may infl uence future acceptance of dysphagia management via telerehabilitation, patients’ perceptions were examined before and after a telerehabilitation assessment session. Forty adult patients with dysphagia(M = 66 years, SD = 16.25) completed pre- and post-session questionnaires which consisted of 14 matched questions worded to suit pre- and post-conditions. Questions explored comfort with the use of telerehabilitation, satisfaction with audio and video quality, benefi ts of telerehabilitation assessments and patients’ preferred assessment modality. Questions were rated on a 5-point scale (1 = strongly disagree, 3 = unsure, 5 = strongly agree). Patients’ comfort with assessment via telerehabilitation was high in over 80% of the group both pre- and post-assessment. Pre-assessment, patients were unsure what to expect with the auditory and visual aspects of the videoconference, however there were signifi cant positive changes reported post-experience. In relation to perceived benefits of telerehabilitation services in general, most patients believed in the value of telerehabilitation and post-assessment this increased to 90 – 100% agreement. Although 92% felt they would be comfortable receiving services via telerehabilitation, 45% of patients indicated ultimate preference for a traditional faceto-face assessment. The data highlight that patients are interested in and willing to receive services via telerehabilitation; however, any concerns should be addressed pre-assessment