Abstract
Event-B!CSP is a combination of Event-B and CSP in which CSP controllers are used in conjunction with Event-B machines to allow a more explicit approach to control flow. Recent results have provided an approach to stepwise refinement of such combinations. This paper presents a simplified Bounded Retransmission Protocol case study, inspired by Abrial’s treatment of this example, to illustrate several aspects new in the approach. The case study includes refinement steps to illustrate four different aspects of this approach to refinement: (1) splitting events; (2) introducing convergent looping behaviour; (3) the relationship between anticipated, convergent, and devolved events; and (4) converging anticipated events.