Common Lisp version of the MaxParts function

;;; The mp function will calculate the maximal number of pieces resulting from C planar cuts through a D-dimensional object.
;;; An example of this in 3-space are the cake numbers, described here: http://www.research.att.com/njas/sequences/A000125
(defun mp (D C)
  (if (>= D C)
    (expt 2 C)
    (if (= D 0)
      1
      (if (= C 0)
        1
        (+ (mp (- D 1) (- C 1)) (mp D (- C 1)))))))