lispdoc - results for subsetp

(subsetp list1 list2 &key key (test #'eql testp) (test-not nil notp))
Function: Return T if every element in LIST1 is also in LIST2.
Example:
(defun set-diff (x y)
  (if (subsetp y x)
      (ordered-set-difference x y)))
Mentioned in:
CLtL2 - 15.5. Using Lists as Sets
HyperSpec - Function SUBSETP
PCL - sets