title: How to prove functions equal, knowing their bodies are equal?
body: <p>How can we prove the following?:</p>
  
  <pre><code>Lemma forfun: forall (A B : nat-&gt;nat), (forall x:nat, A x = B x) -&gt;
                                         (fun x =&gt; A x) = (fun x =&gt; B x).
  Proof.
  </code></pre>