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<h1>Identifiers</h1>
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The valid identifier names are described by the
following regular expression: <tt>[a-zA-Z]([a-zA-Z0-9_])*</tt>

<h2>Examples:</h2>
<ul>
<li><tt>a, B, c2, d2</tt> - valid identifier names.
<li><tt>1, 2a, 3B, 4c5</tt> - <b>in</b>valid identifier names.
</ul>

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