  The analysis and proper documentation of the properties of closed-loop
control software presents many distinct aspects from the analysis of the same
software running open-loop. Issues of physical system representations arise,
and it is desired that such representations remain independent from the
representations of the control program. For that purpose, a concurrent program
representation of the plant and the control processes is proposed, although the
closed-loop system is sufficiently serialized to enable a sequential analysis.
While dealing with closed-loop system properties, it is also shown by means of
examples how special treatment of nonlinearities extends from the analysis of
control specifications to code analysis.
