Graham's notation correctly but perhaps too subtly conveys an
important distinction between endp and
null:
null tests for an empty list.
endp tests if a list is empty.
What's the difference? endp will signal an error if
passed a non-list. null won't.
This actually makes endp a better test in most loops
that step through a list, because it will catch non-lists
immediately.
endp is a relatively recent addition to Lisp and is
underutilized by almost everyone, including myself.
Comments? 
Send mail to Chris
Riesbeck.