title: How do I add two sets?
body: <pre><code>a = {'a', 'b', 'c'} 
  b = {'d', 'e', 'f'}
  </code></pre>
  <p>How do I add the above two sets? I expect the result:</p>
  <pre><code>c = {'a', 'b', 'c', 'd', 'e', 'f'}
  </code></pre>