Retrenchment and System Properties

Retrenchment, introduced to alleviate the excessively str ong demands that refinement sometimes imposes, is most easily applied ‘vertically’, i.e. to individual execution steps, without regard to the sequential composition of those steps. This paper addresses the issue of how system properties, akin to se ts f execution sequences, can be transformed between systems through retr enchment. Property transformers based on simulation relations are introduced , as are transformers of ambivalent properties and constrained property transform ers. Their theory is investigated. The simplifications in the context of regular relations are explored. A number of examples in the discrete and continuous domains are examined.