+; 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))))
+(test (equal (intersection '((1) (2)) '((2) (3)) :test #'equal) '((2))))
+