> A question about the substream issue: Why are there several streams and
> within each streams several substreams? (What is the rationale of having
> exactly two levels in the relations of the virtual streams? One could also
> just
> have several streams or also provide subsubstreams etc.)

I don't know the answer to this question.  There is an example in Section
4 of streams001.pdf, but I cannot construct the general principle from the
example.

Perhaps L'Ecuyer can offer a more extensive explanation; I've CC'ed him
on this e-mail.

Brad Lucier