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<head>
<title>UK TeX FAQ -- question label braket</title>
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<h3>Set specifications and Dirac brackets</h3>
<p>One of the few glaring omissions from TeX’s mathematical
typesetting capabilities is a means of setting separators in the
middle of mathematical expressions. TeX provides primitives called
<code>\</code><code>left</code> and <code>\</code><code>right</code>, which can be used to modify brackets (of
whatever sort) around a mathematical expression, as in:
<code>\left( <expression> \right)</code> — the size of the parentheses is
matched to the vertical extent of the expression.
<p>However, in all sorts of mathematical enterprises one may find oneself
needing a <code>\</code><code>middle</code> command, to be used in expressions like
<blockquote>
<pre>
\left\{ x \in \mathbb{N} \middle| x \mbox{ even} \right\}
</pre>
</blockquote><p>
to specify the set of even natural numbers. The
<a href="FAQ-etex.html">e-TeX system</a>
defines just such a command, but users of Knuth’s original need some
support. Donald Arseneau’s <i>braket</i> package provides commands
for set specifications (as above) and for Dirac brackets (and bras and
kets). The package uses the e-TeX built-in command if it finds
itself running under e-TeX.
<dl>
<dt><tt><i>braket.sty</i></tt><dd><a href="ftp://cam.ctan.org/tex-archive/macros/latex/contrib/misc/braket.sty">macros/latex/contrib/misc/braket.sty</a>
</dl>
<p><p>This question on the Web: <a href="http://www.tex.ac.uk/cgi-bin/texfaq2html?label=braket">http://www.tex.ac.uk/cgi-bin/texfaq2html?label=braket</a>
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