 <p>Your input is incorrect, it should be in the MathML namespace:</p> <pre><code>&lt;math xmlns="http://www.w3.org/1998/Math/MathML"&gt; &lt;apply&gt;&lt;power&gt;&lt;/power&gt;&lt;ci&gt;x&lt;/ci&gt;&lt;cn&gt;2&lt;/cn&gt;&lt;/apply&gt; &lt;/math&gt; </code></pre> <p>Not directly related to your problem but there is a newer, maintained, version of the ctop.xsl stylesheet here</p> <p><a href="https://github.com/davidcarlisle/web-xslt/tree/master/ctop" rel="nofollow">https://github.com/davidcarlisle/web-xslt/tree/master/ctop</a></p>