its members.
<A NAME="nil_term"></A><HR><PRE><B>BOOL nil_term(<A HREF="term.html">Term</A> t);
</B></PRE>This function checks if a term is a "nil", that is,
arity 0 with the official "nil" symbol.   
<A NAME="proper_listterm"></A><HR><PRE><B>BOOL proper_listterm(<A HREF="term.html">Term</A> t);
</B></PRE>This function checks if a term is a proper listterm,
that is, a <A HREF="#nil_term">nil_term</A>(), or a <A HREF="#cons_term">cons_term</A>() whose tail
is a <A HREF="#proper_listterm">proper_listterm</A>()