Temporal logics such as LTL are often used to express safety or correctness properties of programs. However, they cannot model complex formulas known as hyperproperties introducing relations between different execution paths of a same system. In order to do so, the logic HyperLTL adds existential and universal quantifications of path variables to LTL. The model-checking problem, that is, determining if a given representation of a program verifies a HyperLTL property, has been shown to be decidable for finite state systems. In this paper, we prove that this result does not hold for Pushdown Systems nor for the subclass of Visibly Pushdown Systems. We therefore introduce an algorithm that over-approximates the model-checking problem with an automatatheoretic approach. We also detail an under-approximation method based on a phase-bounded analysis of Multi-Stack Pushdown Systems. We then show how these approximations can be used to check security policies.

We introduce a new algorithm that takes a Transition-based Emerson-Lei Automaton (TELA), that is, an ω-automaton whose acceptance condition is an arbitrary Boolean formula on sets of transitions to be seen infinitely or finitely often, and converts it into a Transition-based Parity Automaton (TPA). To reduce the size of the output TPA, the algorithm combines and optimizes two procedures based on a latest appearance record principle, and introduces a partial degeneralization. Our motivation is to use this algorithm to improve our LTL synthesis tool, where producing deterministic parity automata is an intermediate step.

We report on the last four editions of the reactive synthesis competition (SYNTCOMP 2018(SYNTCOMP -2021. We briefly describe the evaluation scheme and the experimental setup of SYNTCOMP. Then, we introduce new benchmark classes that have been added to the SYNTCOMP library and give an overview of the participants of SYNTCOMP. Finally, we present and analyze the results of our experimental evaluations, including a ranking of tools with respect to quantity and quality of solutions.

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