CL-USER> (defun combinations (list)
           (cond 
             ((null list) '(()))
             (t (loop for element in list
                      append (loop for subcombination in (combinations (remove element list))
                                   collect (cons element subcombination))))))
COMBINATIONS
CL-USER> (combinations '(0 1 2 3))
((0 1 2 3) (0 1 3 2) (0 2 1 3) (0 2 3 1) (0 3 1 2) (0 3 2 1) (1 0 2 3)
 (1 0 3 2) (1 2 0 3) (1 2 3 0) (1 3 0 2) (1 3 2 0) (2 0 1 3) (2 0 3 1)
 (2 1 0 3) (2 1 3 0) (2 3 0 1) (2 3 1 0) (3 0 1 2) (3 0 2 1) (3 1 0 2)
 (3 1 2 0) (3 2 0 1) (3 2 1 0))