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<head><title>MEMBER-EQ.html -- ACL2 Version 3.1</title></head>
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<h2>MEMBER-EQ</h2>membership predicate, using <code><a href="EQ.html">eq</a></code> as test
<pre>Major Section: <a href="PROGRAMMING.html">PROGRAMMING</a>
</pre><p>
<code>(Member-eq x lst)</code> equals the longest tail of <code>lst</code> that
begins with <code>x</code>, or else <code>nil</code> if no such tail exists.
<p>
<code>(Member-eq x lst)</code> is provably the same in the ACL2 logic as
<code>(member x lst)</code> and <code>(member-equal x lst)</code>, but it has a stronger
<a href="GUARD.html">guard</a> because it uses <code><a href="EQ.html">eq</a></code> for a more efficient test for whether
<code>x</code> is equal to a given member of <code>lst</code>. Its <a href="GUARD.html">guard</a> requires that
<code>lst</code> is a true list, and moreover, either <code>x</code> is a symbol or
<code>lst</code> is a list of symbols. See <a href="MEMBER-EQUAL.html">member-equal</a> and
see <a href="MEMBER.html">member</a>.
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