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<head><title>SUBSEQ.html -- ACL2 Version 3.1</title></head>
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<h2>SUBSEQ</h2>subsequence of a string or list
<pre>Major Section: <a href="PROGRAMMING.html">PROGRAMMING</a>
</pre><p>
For any natural numbers <code>start</code> and <code>end</code>, where <code>start</code> <code><=</code>
<code>end</code> <code><=</code> <code>(length seq)</code>, <code>(subseq seq start end)</code> is the
subsequence of <code>seq</code> from index <code>start</code> up to, but not including,
index <code>end</code>. <code>End</code> may be <code>nil</code>, which which case it is treated
as though it is <code>(length seq)</code>, i.e., we obtain the subsequence of
<code>seq</code> from index <code>start</code> all the way to the end.
<p>
The <a href="GUARD.html">guard</a> for <code>(subseq seq start end)</code> is that <code>seq</code> is a
true list or a string, <code>start</code> and <code>end</code> are integers (except,
<code>end</code> may be <code>nil</code>, in which case it is treated as <code>(length seq)</code>
for ther rest of this discussion), and <code>0</code> <code><=</code> <code>start</code> <code><=</code>
<code>end</code> <code><=</code> <code>(length seq)</code>.<p>
<code>Subseq</code> is a Common Lisp function. See any Common Lisp
documentation for more information. Note: In Common Lisp the third
argument of <code>subseq</code> is optional, but in ACL2 it is required,
though it may be <code>nil</code> as explained above.
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