title: R markdown (html_pretty) does not show "not equal" symbol properly
body: <p>I found that &quot;html_pretty&quot; output does not properly show the unequal math symbol.</p>
  <p>The following is the minimal reproducible example for it.</p>
  <pre><code>---
  title: &quot;example&quot;
  output:
    prettydoc::html_pretty:
      theme: architect
      highlight: github
      math: katex
  ---
  
  $$
  \mu \neq \mu_0
  $$
  </code></pre>
  <p>This shows
  <a href="https://i.stack.imgur.com/E88m2.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/E88m2.png" alt="enter image description here" /></a></p>
  <p>However, the regular &quot;html_document&quot; format works, showing $\noteq$ as we want.</p>
  <pre><code>---
  title: &quot;Untitled&quot;
  output: html_document
  ---
  
  $$
  \mu \neq \mu_0
  $$
  </code></pre>
  <p>Do you have any idea about the reason? How do I use the unequal symbol in &quot;html_pretty&quot; format?</p>