<p>Could <code>arch-garch</code> become the replacing tag? The two abbreviations are often present together in lecture titles:</p>

<ul>
<li><a href="https://onlinecourses.science.psu.edu/stat510/node/78" rel="nofollow">ARCH/GARCH Models</a></li>
<li><a href="http://www.stern.nyu.edu/rengle/GARCH101.PDF" rel="nofollow">GARCH 101: An Introduction to the Use of ARCH/GARCH models in Applied
Econometrics</a></li>
<li><a href="http://public.econ.duke.edu/~boller/Papers/glossary_arch.pdf" rel="nofollow">Glossary to ARCH (GARCH)</a></li>
</ul>

<p>This way, the single tag could show up when typing the first letters of either <code>arch</code> or <code>garch</code>, in the "tag box".</p>
