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This paper describes a new symbolic model checker, called NUSMV, developed as part of a joint project between CMU and IRST. NUSMV is the result of the reengineering, reimplementation, and, to a limited extent, extension of the CMU SMV model checker. The core of this paper consists of a detailed description of the NUSMV functionalities, architecture, and implementation.

This paper describes the NUXMV symbolic model checker for finiteand infinite-state synchronous transition systems. NUXMV is the evolution of the NUSMV open source model checker. It builds on and extends NUSMV along two main directions. For finite-state systems it complements the basic verification techniques of NUSMV with state-of-the-art verification algorithms. For infinitestate systems, it extends the NUSMV language with new data types, namely Integers and Reals, and it provides advanced SMT-based model checking techniques.Besides extended functionalities, NUXMV has been optimized in terms of performance to be competitive with the state of the art. NUXMV has been used in several industrial projects as verification back-end, and it is the basis for several extensions to cope with requirements analysis, contract based design, model checking of hybrid systems, safety assessment, and software model checking.This work was carried out within the D-MILS project, which is partially funded under the European Commission's Seventh Framework Programme (FP7).

Abstract. Realizability -checking whether a specification can be implemented by an open system -is a fundamental step in the design flow. However, if the specification turns out not to be realizable, there is no method to pinpoint the causes for unrealizability. In this paper, we address the open problem of providing diagnostic information for realizability: we formally define the notion of (minimal) explanation of (un)realizability, we propose algorithms to compute such explanations, and provide a preliminary experimental evaluation.