Complexity in Automation of SOS Proofs: An Illustrative Example

We present a case study in proving invariance for a chaotic dynamical system, the logistic map, based on Positivstellensatz refutations, with the aim of studying the problems associated with developing a completely automated proof system. We derive the refutation using two different forms of the Positivstellensatz and compare the results to illustrate the challenges in defining and classifying the `complexity´ of such a proof. The results show the flexibility of the SOS framework in converting a dynamics problem into a semialgebraic one as well as in choosing the form of the proof. Yet it is this very flexibility that complicates the process of automating the proof system and classifying proof `complexity´