title: Is there an equivalent of the Task.ContinueWith operator in Rx?
body: <p>Is there an equivalent of the Task.ContinueWith operator in Rx?</p>
  
  <p>I'm using Rx with Silverlight,  I am making two webservice calls with the FromAsyncPattern method, and I'd like to do them <em>synchronously</em>.</p>
  
  <pre><code>        var o1 = Observable.FromAsyncPattern&lt;int, string&gt;(client.BeginGetData, client.EndGetData);
          var o2 = Observable.FromAsyncPattern&lt;int, string&gt;(client.BeginGetData, client.EndGetData);
  </code></pre>
  
  <p>Is there an operator (like Zip) that will only start / subscribe to o2 <em>only after</em> o1 returns Completed?<br>
  I handle failure of either web service call the same way.</p>