> (remove-duplicates '(a b d a b c a )) (D B C A) > (remove-duplicates '((a) (a) (b) (a))) ((A) (A) (B) (A)) > (remove-duplicates '((a) (a) (b) (a)) :test #'equal) ((B) (A)) > (remove-duplicates '((1 a) (1 b) (2 a)) :key #'car) ((1 B) (2 A)) > (remove-duplicates '((1 b) (1 a) (2 a)) :key #'car) ((1 A) (2 A))