recognizer for (not necessarily proper) lists
Major Section:  ACL2-BUILT-INS

(listp x) is true when x is either a cons pair or is nil.

Listp has no guard, i.e., its guard is t.

Listp is a Common Lisp function. See any Common Lisp documentation for more information.

To see the ACL2 definition of this function, see pf.