(test (equal (member 4 '((1 . 2) (3 . 4)) :key #'cdr) '((3 . 4))))
(test (member '(2) '((1) (2) (3)) :test #'equal))
+; ADJOIN
+(test (equal (adjoin 1 '(2 3)) '(1 2 3)))
+(test (equal (adjoin 1 '(1 2 3)) '(1 2 3)))
+(test (equal (adjoin '(1) '((1) (2)) :test #'equal) '((1) (2))))
+
; INTERSECTION
(test (equal (intersection '(1 2) '(2 3)) '(2)))
(test (not (intersection '(1 2 3) '(4 5 6))))