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<head><title>SIGNUM.html -- ACL2 Version 3.1</title></head>
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<h2>SIGNUM</h2>indicator for positive, negative, or zero
<pre>Major Section: <a href="PROGRAMMING.html">PROGRAMMING</a>
</pre><p>
<code>(Signum x)</code> is <code>0</code> if <code>x</code> is <code>0</code>, <code>-1</code> if <code>x</code> is negative,
and is <code>1</code> otherwise.
<p>
The <a href="GUARD.html">guard</a> for <code>signum</code> requires its argument to be rational (<a href="REAL.html">real</a>, in
ACL2(r)) number.<p>
<code>Signum</code> is a Common Lisp function. See any Common Lisp
documentation for more information.<p>
From ``Common Lisp the Language'' page 206, we see a definition of
<code>signum</code> in terms of <code><a href="ABS.html">abs</a></code>. As explained elsewhere
(see <a href="ABS.html">abs</a>), the <a href="GUARD.html">guard</a> for <code><a href="ABS.html">abs</a></code> requires its argument to be a
rational (<a href="REAL.html">real</a>, in ACL2(r)) number; hence, we make the same
restriction for <code>signum</code>.
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