title: Find all used references in Excel formula
body: <p>Below is the example set in Excel,</p>
  
  <pre><code>[column1] [column2]
  
  A1  =C3-C5
  
  A2  =((C4-C6)/C6)
  
  A3  =C4*C3
  
  A4  =C6/C7
  
  A5  =C6*C4*C3
  </code></pre>
  
  <p>I need to extract the used references in formulas</p>
  
  <p>For example,</p>
  
  <pre><code>for "A1", I simply need to get the C3 and C5.
  for A2, I need to get the C4 and C6.
  </code></pre>