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<head><title>Help On LaTeX fragile commands</title></head>
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<h1><font size="-2">Hypertext Help with LaTeX</font><br><font color="#cc0000">Fragile and Robust commands</font></h1>
LaTeX commands are either <em>robust</em> or <em>fragile</em>. Fragile
commands need special care <em>if they are part of a moving argument</em>.
<p>
Arguments to some LaTeX commands are called <em>moving arguments</em> because
they may be "moved" to other places in the document. For example, the argument
of <a href="ltx-141.html">Sectioning comands</a> may be moved
to the <a href="ltx-170.html">Table of Contents</a>. Other examples
of moving arguments include:
<ul>
<li>arguments of <a href="caption.html"><tt>\caption</tt></a> commands
<li>terminal input and output, <a href="ltx-174.html"><tt>\typeout</tt></a>
and <a href="ltx-175.html"><tt>\typein</tt></a>
<li>commands that <a href="ltx-264.html">produce page headings</a>
<li>the <a href="ltx-91.html">Letter Environment</a>
<li>the <a href="ltx-324.html"><tt>\thanks</tt></a> command
<li> an <tt>@</tt> expression in the <a href="ltx-202.html">Array</a> or
<a href="ltx-68.html">Tabular</a> environment
</ul>
A fragile command that appears in a moving argument must be preceded by a
<tt>\protect</tt> command. The <tt>\protect</tt> applies only to the
immediately following command; if arguments of this command also contain
fragile commands, the latter must be protected with their own <tt>\protect</tt>.
<h2>Some fragile commands</h2>
The following list is not exhaustive, but illustrates the kind of commands
which are fragile
<ul>
<li>All commands that have an optional argument are fragile.
<li>Environments delimited by <tt>\begin ... \end</tt> are fragile.
<li><a href="ltx-421.html">Display math</a> environment delimited by
<tt>\[ ... \]</tt>
<li><a href="ltx-115.html">Math environment</a> <tt>\( ... \)</tt>
<ul><li>However, <tt>$ ... $</tt> is robust</ul>
<li>Line breaks, <a href="ltx-181.html"><tt>\\</tt></a>
<li><a href="item.html"><tt>\item</tt></a> commands
<li><a href="ltx-231.html"><tt>\footnote</tt></a> commands
</ul>
<h2>Some robust commands</h2>
In general, commands which change <a href="ltx-176.html">Type face or
Type style</a> are robust.
<p>
<a href="ltx-86.html">Length commands</a> are robust and should
<strong>not</strong> be preceded by a <tt>\protect</tt> command. Nor
should a <tt>\protect</tt> command be used in the argument to
<a href="ltx-195.html"><tt>\addtocounter</tt></a> or
<a href="ltx-310.html"><tt>\setcounter</tt></a> command.
<hr>
Return to <a href="ltx-2.html">LaTeX Table of Contents</a>
<hr>
<address>
Revised: Sheldon Green, 29 Sep 1995.
</address>
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