));
Maxima was unable to evaluate the predicate:
       2             2
equal(x  + 2 x + 1, x  - 2 x - 1)
 -- an error.  Quitting.  To debug this try debugmode(true);
(%i5) prederror : false;
(%o5)                         false
(%i6) is (equal (aa, bb));
(%o6)                        unknown
</pre>
<p>Einige weitere Operatoren werten <code>equal</code> und <code>notequal</code> zu einem
booleschen Wert aus.
</p>
<pre class="example">(%i1) if equal (y, y - 1) then FOO else BAR;
(%o1)                          