title: Getting mutually exclusive keys of two NSDictionary items
body: <p>I have two different NSDictionary objects where there are keys that belong to both collections while there are some keys present only in the 1st dictionary and similarly, few keys are found in the 2nd dictionary but not in the 1st.</p>
  
  <p>Is there an efficient way to do a set comparison to extract the keys present in the 1st dictionary that do not exist in the 2nd?</p>
  
  <p>Basically, in the standard Venn diagram, the elements of Set A that do not intersect with Set B.</p>