Satisfiability Modulo Theories (SMT) is the problem of deciding the satisfiability of a first-order formula with respect to some theory or combination of theories; Verification Modulo Theories (VMT) is the problem of analyzing the reachability for transition systems represented in terms of SMT formulae.

 

In this seminar, we tackle the problems of SMT and VMT over the theories of polynomials over the reals (NRA), over the integers (NIA), and of NRA augmented with transcendental functions (NTA). We propose a New abstraction-refinement approach called Incremental Linearization. The idea is to abstract nonlinear multiplication and transcendental functions as uninterpreted functions in an abstract domain limited to linear arithmetic with uninterpreted functions. The uninterpreted functions are incrementally axiomatized by means of upper- and lower-bounding piecewise-linear constraints. In the case of transcendental functions, particular care is required to ensure the soundness of the abstraction. The method has been implemented in the

MathSAT SMT solver, and in the nuXmv VMT model checker. An extensive experimental evaluation on a wide set of benchmarks from verification and mathematics demonstrates the generality and the effectiveness of our approach.

Moreover, the proposed technique is an enabler for the (nonlinear) VMT problems arising in practical scenarios with design environments such as Simulink. This capability has been achieved by integrating nuXmv with Simulink using a compilation-based approach and is evaluated on an industrial-level case study.