. Similarly, if &quot;PLUTO&quot; is already an 
      element of asteroids, the contents of asteroids remain unchanged. 
 </PRE>
<h4><a name="Restrictions">Restrictions</a></h4>
<PRE>
 
   1)  String comparisons performed by this routine are Fortran-style:
       trailing blanks in the input set or key value are ignored.
       This gives consistent behavior with CSPICE code generated by
       the f2c translator, as well as with the Fortran SPICE Toolkit.
      
       Note that this behavior is not ident