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HyperLTL is an extension of linear-time temporal logic for the specification of hyperproperties, i.e., temporal properties that relate multiple computation traces. HyperLTL can express information flow policies as well as properties like symmetry in mutual exclusion algorithms or Hamming distances in error-resistant transmission protocols. Previous work on HyperLTL model checking has focussed on the alternation-free fragment of HyperLTL, where verification reduces to checking a standard trace property over an appropriate self-composition of the system. The alternation-free fragment does, however, not cover general hyperliveness properties. Universal formulas, for example, cannot express the secrecy requirement that for every possible value of a secret variable there exists a computation where the value is different while the observations made by the external observer are the same. In this paper, we study the more difficult case of hyperliveness properties expressed as HyperLTL formulas with quantifier alternation. We reduce existential quantification to strategic choice and show that synthesis algorithms can be used to eliminate the existential quantifiers automatically. We furthermore show that this approach can be extended to reactive system synthesis, i.e., to automatically construct a reactive system that is guaranteed to satisfy a given HyperLTL formula.

Abstract. We introduce the reactive synthesis competition (SYNTCOMP), a long-term effort intended to stimulate and guide advances in the design and application of synthesis procedures for reactive systems. The first iteration of SYNTCOMP is based on the controller synthesis problem for finite-state systems and safety specifications. We provide an overview of this problem and existing approaches to solve it, and report on the design and results of the first SYNTCOMP. This includes the definition of the benchmark format, the collection of benchmarks, the rules of the competition, and the five synthesis tools that participated. We present and analyze the results of the competition and draw conclusions on the state of the art. Finally, we give an outlook on future directions of SYNTCOMP.

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The reactive synthesis problem is to compute a system satisfying a given specification in temporal logic. Bounded synthesis is the approach to bound the maximum size of the system that we accept as a solution to the reactive synthesis problem. As a result, bounded synthesis is decidable whenever the corresponding verification problem is decidable, and can be applied in settings where classic synthesis fails, such as in the synthesis of distributed systems. In this paper, we study the constraint solving problem behind bounded synthesis. We consider different reductions of the bounded synthesis problem of linear-time temporal logic (LTL) to constraint systems given as boolean formulas (SAT), quantified boolean formulas (QBF), and dependency quantified boolean formulas (DQBF). The reductions represent different trade-offs between conciseness and algorithmic efficiency. In the SAT encoding, both inputs and states of the system are represented explicitly; in QBF, inputs are symbolic and states are explicit; in DQBF, both inputs and states are symbolic. We evaluate the encodings systematically using benchmarks from the reactive synthesis competition (SYNTCOMP) and state-of-theart solvers. Our key, and perhaps surprising, empirical finding is that QBF clearly dominates both SAT and DQBF.

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We report on the benchmarks, participants and results of the third reactive synthesis competition (SYNTCOMP 2016). The benchmark library of SYNTCOMP 2016 has been extended to benchmarks in the new LTL-based temporal logic synthesis format (TLSF), and 2 new sets of benchmarks for the existing AIGER-based format for safety specifications. The participants of SYNTCOMP 2016 can be separated according to these two classes of specifications, and we give an overview of the 6 tools that entered the competition in the AIGER-based track, and the 3 participants that entered the TLSF-based track. We briefly describe the benchmark selection, evaluation scheme and the experimental setup of SYNTCOMP 2016. Finally, we present and analyze the results of our experimental evaluation, including a comparison to participants of previous competitions and a legacy tool. IntroductionSince the definition of the problem more than 50 years ago [16], the automatic synthesis of reactive systems from formal specifications is one of the major challenges of computer science. Research into the basic questions related to the problem has led to a large body of theoretical results, but their impact on the practice of system design has been rather limited. To increase the impact of theoretical advancements in synthesis, the reactive synthesis competition (SYNTCOMP) has been founded in 2014 [27]. The competition is designed to foster research in scalable and user-friendly implementations of synthesis techniques by establishing a standard benchmark format, maintaining a challenging public benchmark library, and providing a dedicated and independent platform for the comparison of tools under consistent experimental conditions.The venues. A design choice for the first two competitions was to focus on safety properties specified as monitor circuits in an extension of the AIGER format known from the hardware model checking competition [15,25]. SYNTCOMP 2016 introduces the first major extension of the competition: in addition to the existing competition track, we introduce a new track that is based on properties in full linear temporal logic (LTL), given in the temporal logic synthesis format (TLSF) recently introduced by Jacobs, Klein and Schirmer [29].The organization team of SYNTCOMP 2016 consisted of R. Bloem and S. Jacobs, with technical assistance from J. Kreber for the setup and execution, and from F. Klein for the integration of TLSF.The rest of this paper describes the design, benchmarks, participants, and results of SYNTCOMP 2016. We present the benchmark set for SYNTCOMP 2016 in Section 2, followed by a description of the setup, rules and execution of the competition in Section 3. In Section 4 we give an overview of the participants of SYNTCOMP 2016, focusing on changes compared to last year's participants. Finally, the experimental results are presented and analyzed in Section 5.Note that more details on the goals and design of the competition can be found in the sister paper that discusses the design of SYNTCOMP in 2016 and the future [26]. Be...