The function process-unstop
unstops the process process if it is stopped.
process must be a full process (that is, not one created by *current-process*).
If process was stopped (by process-stop), it is unstopped and resumes execution.
result is t
if process was stopped, and nil
otherwise.
There is a discussion of a typical use of process-unstop
in the section Stopping and unstopping processes.
LispWorks User Guide and Reference Manual - 20 Sep 2017