agent Send = acc.Sending;
agent Sending = 'send.Wait;
agent Wait = ack.Send + error.Sending;

agent Rec = trans.Del;
agent Del = 'del.Ack;
agent Ack = 'ack.Rec;

agent Med = send.Med';
agent Med' = (tau.Err + 'trans.Med);
agent Err = 'error.Med;

set L = {send, trans, ack, error};

agent Impl = (Send | Med | Rec) \ L;

agent Spec = acc.'del.Spec;