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-<head>
-<title>UK TeX FAQ -- question label hash</title>
-</head><body>
-<h3>Defining macros within macros</h3>
-<p/>The way to think of this is that <code>##</code> gets replaced by <code>#</code> in just the
-same way that <code>#1</code> gets replaced by &#8216;whatever is the first argument&#8217;.
-<p/>So if you define a macro and use it as:
-<blockquote>
-<pre>
-\def\a#1{+++#1+++#1+++#1+++} \a{b}
-</pre>
-</blockquote><p>
-the macro expansion produces &#8216;+++b+++b+++b+++&#8217;,
-which people find normal. However, if we now replace part of the macro:
-<blockquote>
-<pre>
-\def\a#1{+++#1+++\def\x #1{xxx#1}}
-</pre>
-</blockquote><p>
-<code>\</code><code>a{b}</code> will expand to &#8216;+++b+++<code>\def\x b{xxxb}</code>&#8217;. This
-defines <code>\</code><code>x</code> to be a macro <em>delimited</em> by <code>b</code>, and taking no
-arguments, which people may find strange, even though it is just a
-specialisation of the example above. If you want <code>\</code><code>a</code> to
-define <code>\</code><code>x</code> to be a macro with one argument, you need to write:
-<blockquote>
-<pre>
-\def\a#1{+++#1+++\def\x ##1{xxx##1}}
-</pre>
-</blockquote><p>
-and <code>\</code><code>a{b</code>} will expand to
-&#8216;+++b+++<code>\def\x #1{xxx#1}</code>&#8217;, because <code>#1</code> gets replaced by &#8216;b&#8217;
-and <code>##</code> gets replaced by <code>#</code>.
-<p/>To nest a definition inside a definition inside a definition then
-you need <code>####1</code>, as at each stage <code>##</code> is replaced by
-<code>#</code>. At the next level you need 8 <code>#</code>s each time, and so on.
-<p/><p>This question on the Web: <a href="http://www.tex.ac.uk/cgi-bin/texfaq2html?label=hash">http://www.tex.ac.uk/cgi-bin/texfaq2html?label=hash</a>
-</body>