title: excel shared formula expansion
body: <p>I am using the OpenXML libraries from C# to read Excel files.</p>
  
  <p>One of my requirements is to be able to show the exact formula for each cell that has one. The OpenXML encoded file uses "shared formulas" to reduce file size.</p>
  
  <p>Like this:</p>
  
  <pre><code>D3 : &lt;x:f t="shared" ref="D3:D6" si="1" &gt;D2+C3&lt;/x:f&gt;&lt;x:v &gt;130&lt;/x:v&gt;
  D4 : &lt;x:f t="shared" si="1"  /&gt;&lt;x:v &gt;136&lt;/x:v&gt;
  D5 : &lt;x:f t="shared" si="1"  /&gt;&lt;x:v &gt;141&lt;/x:v&gt;
  D6 : &lt;x:f t="shared" si="1"  /&gt;&lt;x:v &gt;147&lt;/x:v&gt;
  </code></pre>
  
  <p>Its a fairly simple root formula in the example above (D2+C3) and obviously these can be arbitrarily complex.</p>
  
  <p>What I want to know is if there is a library or example code available that takes any lower cell (e.g. D4,D5,D6) and return the "unshared" formula?</p>
  
  <p>e.g. for D6 this would return "D5+C6"</p>