title: common lisp how to set an element in a 2d array?
body: <p>I think I just use <code>setq</code> (or <code>setf</code>, I'm not really sure the difference), but I don't understand how to reference the <code>[i][j]</code>-th element in an array in lisp.</p>
  
  <p>My start condition is this:</p>
  
  <pre><code>? (setq x (make-array '(3 3)))
  #2A((0 0 0) (0 0 0) (0 0 0))
  </code></pre>
  
  <p>I want to alter, say, the 2nd item of the 3rd "row" to give this:</p>
  
  <pre><code>? ;;; What Lisp code goes here?!
  #2A((0 0 0) (0 0 0) (0 "blue" 0))
  </code></pre>
  
  <p>The following, which I would have thought close, gives an error:</p>
  
  <pre><code>(setq (nth 1 (nth 2 x)) "blue")
  </code></pre>
  
  <p>So what's the correct syntax?</p>
  
  <p>Thanks!</p>