(LETREC APPEND
  (APPEND LAMBDA (X Y)
    (IF (EQ X (QUOTE NIL)) Y
        (CONS (CAR X) (APPEND (CDR X) Y)))))&

(6 2 NIL 3 (1 (0 . 0) 2 NIL 14 8 (1 (0 . 1) 9) (2 NIL 1 (0 . 1) 13 1 (0 . 0)
11 13 1 (1 . 0) 4 1 (0 . 0) 10 13 9) 5) 13 3 (1 (0 . 0) 5) 7 4 21) &