e>select</code> filtering.

<p>Some of these predicates are of general use: <code><a
href="refI.html#isa/2">isa/2</a></code> can be used to check for a type,
<code><a href="refS.html#same/3">same/3</a></code> checks for a definite value,
<code><a href="refB.html#bool/3">bool/3</a></code> looks if the value is
non-<code>NIL</code>. These predicates are rather independent of the <code><a
href="refR.html#+relation">+relation</a></code> type.

<p><code><a href="refR.html#range/3">range/3</a></code> checks wheth