1 (defun tan-cf (x k)
2        (labels ((tan-step (i)
3 			  (/ (if (= i 1)
4 				 x
5 			       (square x))
6 			     (- (1- (* i 2))
7 				(if (= i k)
8 				    0
9 				  (tan-step (1+ i)))))))
10 	       (tan-step 1)))