 nohighlight">\(x\)</span> followed by <span class="math notranslate nohighlight">\(y\)</span>.  For example,</p>
<div class="math notranslate nohighlight">
\[
\one\hash\one + \hash \hash = \one\hash\one  \hash \hash.
\]</div>
<p>This operation is associative: <span class="math notranslate nohighlight">\(x + (y+z) = (x+y) + z\)</span>.</p>
<p>The <em>empty word</em> <span class="math notranslate nohighlight">\(\eps\)</span> is an identity element for it:
<span class="math notranslate nohighlight">\(x + \eps