Thank you for the additional references to the publications of Pierre L'Ecuyer;
I am still working on how to make essentially the same functionality available
through the interface for this SRFI.

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.)