title: Multiline equations when converting from jupyter notebook to tex
body: <p>I'm using <code>nbconvert</code> to convert from Jupyter notebook containing MathJax equations to tex files. One problem is that multi-line equations which contain alignment, i.e.</p>
  
  <pre><code>$$
  /begin{align}
  ...
  /end{align}
  $$
  </code></pre>
  
  <p>are converted in tex to</p>
  
  <pre><code>\[
  \begin{align}
  ...
  \end{align}
  \]
  </code></pre>
  
  <p>And it yield a tex bug: `unexpected close display math ] after \begin{document}</p>