Replace an item in a list in Common Lisp?

Question

I have a list of things (I\'ll call it L), an index(N) and a new thing(NEW). If I want to replace the thing in L at N with NEW, what is the best way to do this? Should I get the

Answer 1

(defun replace-nth-from-list  (list n elem)  
      (cond  
        ((null list) ())  
        (t (append (subseq list 0 n) elem (subseq list (+ 1 n)(length list))))))