Grigore Rosu and Traian Florin Serbanuta gave a definition of SIMPLE in the K framework. They wrote:
SIMPLE is intended to be a pedagogical and research language that captures the essence of the imperative programming paradigm, extended with several features often encountered in imperative languages.
SIMPLE is a somewhat larger imperative language than IMP. Its CBS illustrates further features of the framework. The start of the specification of SIMPLE in CBS is at SIMPLE-Start.
Note that the CBS specification of SIMPLE does not yet include threads, since funcons for threads are not yet available.