title: NSString lookup in NSSet
body: <p>How may I find a certain string (value) in an NSSet?<br>
  Must this be done using predicates? If so, how?</p>
  
  <pre><code>NSMutableSet *set = [[NSMutableSet alloc] init];
  [set addObject:[[[NSString alloc] initWithFormat:@"String %d", 1] autorelease]];
  [set addObject:[[[NSString alloc] initWithFormat:@"String %d", 2] autorelease]];
  [set addObject:[[[NSString alloc] initWithFormat:@"String %d", 3] autorelease]];
  </code></pre>
  
  <p>Now I want to check if 'String 2' exists in the set.<br></p>