Combining Lists with Non-stably Infinite Theories

In program verification one has often to reason about lists over elements of a given nature. Thus, it becomes important to be able to combine the theory of lists with a generic theory T modeling the elements. This combination can be achieved using the Nelson-Oppen method only ifT is stably infinite. The goal of this paper is to relax the stable-infiniteness requirement. More specifically, we provide a new method that is able to combine the theory of lists with any theory T of the elements, regardless of whether T is stably infinite or not. The crux of our combination method is to guess an arrangement over a set of variables that is larger than the one considered by Nelson and Oppen. Furthermore, our results entail that it is also possible to combine T with the more general theory of lists with a length function