title: Combine two Observable that emit different types
body: <p>I have two Observables, one <code>Observable&lt;String&gt;</code>, one <code>Observable&lt;Boolean&gt;</code>. Can I combine them so I receive </p>
  
  <pre><code>@Override
  public void call(String s, Boolean b) {
  
  }
  </code></pre>
  
  <p>when both operations are finished?</p>