  The most important notations of Communicating Sequential Process(CSP) are the
process and the prefix (event)$\rightarrow$(process) operator. While we can
formally apply the $\rightarrow$ operator to define a live process's behavior,
the STOP process, which usually resulted from deadlock, starving or livelock,
is lack of formal description, defined by most literatures as "doing nothing
but halt". In this paper, we argue that the STOP process should not be
considered as a black box, it should follow the prefix $\rightarrow$ schema and
the same inference rules so that a unified and consistent process algebra model
can be established. In order to achieve this goal, we introduce a special event
called "nil" that any process can take. This nil event will do nothing
meaningful and leave nothing on a process's observable record. With the nil
event and its well-defined rules, we can successfully use the $\rightarrow$
operator to formally describe a process's complete behavior in its whole life
circle. More interestingly, we can use prefix $\rightarrow$ and nil event to
fully describe the STOP process's internal behavior and conclude that the
STOP's formal equation can be given as simple as STOP$_{\alpha X} = \mu$ X. nil
$\rightarrow$ X.
