Improving Convergence Rate Of IC3
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IC3, a well-known model checker, proves a property of a state system ξ by building a sequence of formulas F_0,...,F_k. Formula F_i, 0 ≤ i ≤ k over-approximates the set of states reachable in at most i transitions. The basic algorithm of IC3 cannot guarantee that the value of k never exceeds the reachability diameter of ξ. We describe an algorithm called IC4 that gives such a guarantee. (IC4 stands for "IC3 + Improved Convergence"). One can also argue that the average convergence rate of IC4 is better than for IC3. This improvement is achieved at a cost that, in particular, involves generation of a small set of reachable states. We present the theory behind IC4 and describe techniques for improving its efficiency. Since we do not provide any experimental data yet, the comparison of performance of IC3 and IC4 is an open question. At the same time, we describe a few important applications that are unique to IC4 due to computation of reachable states.
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