I need to write a lisp function that adds x to the nth item of a list. For example, (add 5 2 '(3 1 4 6 7)) returns (3 6 4 6 7). 

choosing nthitem is

(defun nthitem (n list)
  (cond ((equal n 1) (car list))
        (t (nthitem (-n 1) (cdr list)))))


and adding x to a list is:

(defun addto (x list)
  (cond ((null list) nil)
        (t (cons (+ x (car list)) 
                 (addto x (cdr list))))))


But i cannot combine these two together.


Question: What to call "Cancel" when "Cancel" is already the default action?
Answer: I think that the shown image had a good idea of emulating the user's thoughts, some other good ideas would be:


Nevermind
Abort
Undo
Done
Get me out of here!
Call off
Zap


IMO: Nevermind and Done are the best.