Automated verification of Szymanski's algorithm

The algorithm for mutual exclusion proposed by B. Szymanski is an interesting challenge for verification methods and tools. Several full proofs have been described in the literature, but they seem to require lengthy interactive sessions with powerful theorem provers. As far as this algorithm makes use of only the most elementary facts of arithmetics, we conjectured that a simple, non-interactive proof should exist; this paper gives such a proof, describes its development and how an elementary tool has been used to complete the verification.