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<head><title>UNION-EQUAL.html -- ACL2 Version 3.1</title></head>
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<h2>UNION-EQUAL</h2>union of two lists
<pre>Major Section: <a href="PROGRAMMING.html">PROGRAMMING</a>
</pre><p>
<code>(Union-equal x y)</code> equals a list whose members
(see <a href="MEMBER-EQUAL.html">member-equal</a>) contains the members of <code>x</code> and the members
of <code>y</code>. More precisely, the resulting list is the same as one
would get by first deleting the members of <code>y</code> from <code>x</code>, and then
concatenating the result to the front of <code>y</code>.
<p>
The <a href="GUARD.html">guard</a> for <code>union-equal</code> requires both arguments to be true
lists. Essentially, <code>union-equal</code> has the same functionality as
the Common Lisp function <code>union</code>, except that it uses the <code><a href="EQUAL.html">equal</a></code>
function to test membership rather than <code><a href="EQL.html">eql</a></code>. However, we do not
include the function <code>union</code> in ACL2, because the Common Lisp
language does not specify the order of the elements in the list that
it returns.
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