lispdoc - results for listp

(listp object)
Function: Return true if OBJECT is a LIST, and NIL otherwise.
Example:
(defun arg3 (instr)
  (if (listp instr)
      (fourth instr)))
Mentioned in:
CLtL2 - 15.1. Conses
CLtL2 - 6.2.2. Specific Data Type Predicates
HyperSpec - Function LISTP
On Lisp - Need for Macros
On Lisp - Operations on Lists
PCL - list manipulation functions