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Craig interpolation is a well known method of abstraction successfully used in both hardware and software model checking. The logical strength of interpolants can affect the quality of approximations and consequently the performance of the model checkers. Recently, it was observed that for the same resolution proof a complete lattice of interpolants ordered by strength can be derived. Most state-of-the-art model checking techniques based on interpolation subject the interpolants to constraints that ensure efficient verification as, for example, in transition relation approximation for bounded model checking, counterexample-guided abstraction refinement and function summarization for software update checking. However, in general, these verification-specific constraints are not satisfied by all possible interpolants. The paper analyzes the restrictions within the lattice of interpolants under which the required constraints are satisfied. This enables investigation of the effect of the strength of interpolants on the particular techniques, while preserving their soundness. As an additional benefit, combination of this result with proof manipulation procedures allows the use of optimized solvers to generate interpolants of different strengths for various model checking techniques.

Graphical level of detail (LOD) is a set of techniques for coping with the issue of limited computational resources by reducing the graphical detail of the scene far from the observer. Simulation LOD reduces quality of the simulation at the places unseen. Contrary to graphical LOD, simulation LOD has been almost unstudied. As a part of our ongoing effort on a large virtualstorytelling game populated by tens of complex virtual humans, we have developed and implemented a set of simulation LOD algorithms for simplifying virtual space and behaviour of virtual humans. The main feature of our technique is that it allows for several degrees of detail, i.e. for gradual varying of simulation quality. In this paper, we summarise the main lessons learned, introduce the prototype implementation called IVE and discuss the possibility of scaling our technique to other applications featuring virtual humans.

Software is not created at once. Rather, it grows incrementally version by version and evolves long after being first released. To be practical for software developers, the software verification tools should be able to cope with changes. In this paper, we present a tool, eVolCheck, that focuses on incremental verification of software as it evolves. During the software evolution the tool maintains abstractions of program functions, function summaries, derived using Craig interpolation. In each check, the function summaries are used to localize verification of an upgrade to analysis of the modified functions. Experimental evaluation on a range of various benchmarks shows substantial speedup of incremental upgrade checking of eVolCheck in contrast to checking each version from scratch.

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Abstract. Model checking tools based on the iterative refinement of predicate abstraction (e.g., Slam and Blast) often feature a specification language for expressing complex behavior rules. The source code under verification is instrumented by artificial variables and statements in order to transform the problem of checking such a rule into the problem of program location reachability. This way, the source code get bloated and additional predicates have to be discovered and tracked during the verification. We suggest that a significant performance improvement can be achieved by tracking state of the behavior rules aside from the source code instead of instrumenting them. We have implemented an extension to Blast, which accepts a specification language (a simplified version of behavior protocols), and checks its validity without modifying the input source code. An experiment with two Linux kernel drivers confirms the performance gain using the extension.

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