title: How do I weak link frameworks on Xcode 4?
body: <p>I need to weak link some framework with my target.<br>
  But I can't find how to do it...</p>
  
  <p>If I try to run my project on 3.2 iPad simulator i get the following error:</p>
  
  <pre><code>dyld: Library not loaded: /System/Library/Frameworks/iAd.framework/iAd
  Reason : Image not found
  </code></pre>
  
  <p>Thanks !</p>