lispdoc - results for intersection

(intersection list1 list2 &key key (test #'eql testp) (test-not nil notp))
Function: Return the intersection of LIST1 and LIST2.
Example:
(defun prefer-disjoint (x y)
  (if (intersection (sem x) (sem y))
      -1))
Mentioned in:
CLtL2 - 15.5. Using Lists as Sets
HyperSpec - Function INTERSECTION, NINTERSECTION
PCL - sets