tem))
 @Item={B1}
 @Item={B2}
 @Item={B3}
 @Item={B4}
-> NIL
: (? (select (@Item) ((nr +Item (1 . 4)))))
 @Item={B1}
 @Item={B2}
 @Item={B3}
 @Item={B4}
-> NIL
</pre>


<p><hr>
<h3><a id="interaction">Interaction of Generator Clauses</a></h3>

<p><code>select</code> is mostly useful if more than one generator clause is
involved. The tree search parameters of all clauses are meant to form a logical
<code>AND</code>. Only those objects should be returned, for which all search
parameters (and the associated fi