One of the main challenges of reactive synthesis, an automated procedure to obtain a correct-by-construction reactive system, is to deal with unrealizable speci cations. Existing approaches to deal with unrealizability, in the context of GR(1), an expressive assumeguarantee fragment of LTL that enables e cient synthesis, include the generation of concrete counter-strategies and the computation of an unrealizable core. Although correct, such approaches produce large and complicated counter-strategies, o en containing thousands of states. is hinders their use by engineers.In this work we present the Justice Violations Transition System (JVTS), a novel symbolic representation of counter-strategies for GR(1). e JVTS is much smaller and simpler than its corresponding concrete counter-strategy. Moreover, it is annotated with invariants that explain how the counter-strategy forces the system to violate the speci cation. We compute the JVTS symbolically, and thus more e ciently, without the expensive enumeration of concrete states. Finally, we provide the JVTS with an on-demand interactive concrete and symbolic play.We implemented our work, validated its correctness, and evaluated it on 14 unrealizable speci cations of autonomous Lego robots as well as on benchmarks from the literature. e evaluation shows not only that the JVTS is in most cases much smaller than the corresponding concrete counter-strategy, but also that its computation is faster.
CCS CONCEPTS•So ware and its engineering →Formal methods; So ware verication;