title: context free grammar issue
body: <p>I need help with my context-free grammar for this language:</p>
  
  <pre><code>{b^4 n^m bd^n n^3n+m | m,n &gt;= 0}
  </code></pre>
  
  <p>So far I got this:</p>
  
  <pre><code>S-&gt; bbbbXbY
  X-&gt; n | E
  Y-&gt; dYnnnX
  </code></pre>