Generation of Minimum Tree-Like Witnesses for Existential CTL

An advantage of model checking is its ability to generate witnesses or counterexamples. Approaches exist to generate small or minimum witnesses for simple unnested formulas, but no existing method guarantees minimality for general nested ones. Here, we give a definition of witness size, use edge-valued decision diagrams to recursively compute the minimum witness size for each subformula, and describe a general approach to build minimum tree-like witnesses for existential CTL. Experimental results show that for some models, our approach is able to generate minimum witnesses while the traditional approach is not.