title: Transitive closure of identity relation
body: <p>I am not able to prove the the following <code>lemma</code> in <a href="http://en.wikipedia.org/wiki/Isabelle_(proof_assistant)" rel="nofollow">Isabelle</a>:</p>
  
  <pre><code>lemma "Id^* = Id"
  </code></pre>
  
  <p>Any ideas on how to prove this?</p>