Defining a function called simp, with one parameter called L.

Is the parameter a simple flat list of atoms?

It assumes that it will be given a list, but doesn't bother
checking.

CL-USER> (defun simp (L)
	   (if (null L)
	       t
	       (if (atom (car L))
		   (simp (cdr L))
		   nil)))
SIMP
CL-USER> (simp '(2 4 5 6 3 cat p))
T
CL-USER> (simp '(3 4 (3 1) pppp))
NIL
CL-USER> (simp '())
T
CL-USER> (simp 'x)
Invoking restart: Return to SLIME's top level.
; Evaluation aborted on #<TYPE-ERROR #xC822706>.