{{ template "_internal/disqus.html" . }}

<script src="//yihui.name/js/math-code.js"></script>
<script async src="//cdn.bootcss.com/mathjax/2.7.1/MathJax.js?config=TeX-MML-AM_CHTML"></script>

<script async src="//yihui.name/js/center-img.js"></script>