title: Cannot convert ipython notebook to pdf
body: <p>I'm running into an error during conversion from Jupyter Notebook to PDF:</p>
  <pre><code>nbconvert failed: PDF creating failed
  </code></pre>
  <p>Then I tried running the pdf-converter from the command line and received the following error:</p>
  <pre><code>! Missing $ inserted.
  &lt;inserted text&gt;
                  $
  l.291 ... Till att börja med har vi \$\frac{1}{2}
  
  ?
  ! Emergency stop.
  &lt;inserted text&gt;
                  $
  l.291 ... Till att börja med har vi \$\frac{1}{2}
  
  !  ==&gt; Fatal error occurred, no output PDF file produced!
  </code></pre>
  <p>I then get a line of exceptions ending with:</p>
  <pre><code>OSError: PDF creating failed
  </code></pre>
  <p>I have looked through the document and I found no unmatched <code>$</code> anywhere.</p>