pattern
<code>lpeg.S("+-*/")</code> matches any arithmetic operator.
</p>

<p>
Note that, if <code>s</code> is a character
(that is, a string of length 1),
then <code>lpeg.P(s)</code> is equivalent to <code>lpeg.S(s)</code>
which is equivalent to <code>lpeg.R(s..s)</code>.
Note also that both <code>lpeg.S("")</code> and <code>lpeg.R()</code>
are patterns that always fail.
</p>


<h3><a name="op-v"></a><code>lpeg.V (v)</code></h3>
<p>
This operation creates a non-terminal (a <em>variable</em>)
for a grammar.