xtval</CODE
> within that session simply return the
   preallocated values without touching the sequence object.  So, any
   numbers allocated but not used within a session will be lost when
   that session ends, resulting in <SPAN
CLASS="QUOTE"
>"holes"</SPAN
> in the
   sequence.
  </P
><P
>   Furthermore, although multiple sessions are guaranteed to allocate
   distinct sequence values, the values might be generated out of
   sequence when all the sessions are considered.  For example, with
   a <TT
CLAS