Editing Communicating sequential processes (section)

=== Primitives ===
CSP provides two classes of primitives in its process algebra: events and primitive processes.

;Events

Events represent communications or interactions. They are assumed to be instantaneous, and their communication is all that an external ‘environment’ can know about processes. An event is communicated only if the environment allows it. If a process does offer an event and the environment allows it, then that event ''must'' be communicated. Events may be atomic names (e.g. {{mvar|on}}, {{mvar|off}}), compound names (e.g. {{mvar|valve.open}}, {{mvar|valve.close}}), or input/output events (e.g. {{mvar|mouse?xy}}, {{mvar|screen!bitmap}}). The set of all events is denoted <math>\Sigma</math>.<ref name="ucs">{{cite book |last1=Roscoe |first1=A.W. |date=2010 |title=Understanding Concurrent Systems |series=Texts in Computer Science |doi=10.1007/978-1-84882-258-0 |isbn=978-1-84882-257-3 }}</ref>

;Primitive processes

Primitive processes represent fundamental behaviors: examples include <math>\mathrm{STOP}</math> (the process that immediately deadlocks), and <math>\mathrm{SKIP}</math> (the process that immediately terminates successfully).<ref name="ucs"/>