Geoff Smith asks for a reference for SPAS. I am afraid there isn't a
very useful one. You might quote the "User's Reference Manual" for
version 2.5 of SPAS of 1989, written largely by Volkmar Felsch,
although his authorship is not mentioned on the title page; what is
given there is just the place of origin "Lehrstuhl D f\"ur Mathematik,
RWTH Aachen" since the manual was started with some descriptions
written by students. There is no other publication that you can quote.

However since a very substantial part of SPAS consists of several
programs written as standalone programs e.g. by George Havas and
others, as stated very explicitely in the introduction of the manual,
for a particular computation it may be not only more appropriate but
also more informative to quote these programs and the publications on
them that can be found from that introduction and the bibliography of
the manual.

Joachim Neubueser