One easy algorithm to implement as a recursive function is factorial.
;;Compute the factorial for any n >= 0. Precondition: n >= 0, n is an integer.
(defun factorial (n)
(cond
((= n 0) 1) ;; Special case, 0! = 1
((= n 1) 1) ;; Base case, 1! = 1
(t
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