title: NSPredicate to-many relationships
body: <p>How can I find all the categories that have subcategories with more than 1 items? 
  I am using the following code, but I get "multiple to-many keys not allowed here".</p>
  
  <p>Do I need to use a SUBQUERY? </p>
  
  <pre><code>NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Categories"];
  NSPredicate *predicate = [NSPredicate predicateWithFormat:@"ANY subcategories.items &gt; 0"];
  [request setPredicate:predicate];
  </code></pre>
  
  <p>Help! :)</p>