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<head><title>ABS.html -- ACL2 Version 3.1</title></head>
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<h2>ABS</h2>the absolute value of a real number
<pre>Major Section: <a href="PROGRAMMING.html">PROGRAMMING</a>
</pre><p>
<code>(Abs x)</code> is <code>-x</code> if <code>x</code> is negative and is <code>x</code> otherwise.
<p>
The <a href="GUARD.html">guard</a> for <code>abs</code> requires its argument to be a rational (<a href="REAL.html">real</a>,
in ACL2(r)) number.<p>
<code>Abs</code> is a Common Lisp function. See any Common Lisp documentation
for more information.<p>
From ``Common Lisp the Language'' page 205, we must not allow
complex <code>x</code> as an argument to <code>abs</code> in ACL2, because if we did we
would have to return a number that might be a floating point number
and hence not an ACL2 object.
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