A simple proof of three properties on Simpson's 4-slot Algorithm

In this paper we present an invariance proof of three properties on Simpson's 4-slot algorithm, i.e. data-race freedom, data coherence and data freshness, which together implies linearisability of the algorithm. It is an extension of previous works whose proof focuses mostly on data-race freedom. In addition, our proof uses simply inductive invariants and transition invariants, whereas previous work uses more sophisticated machinery like separation logics, rely-guarantee or ownership transfer.