How to cite GP/Pari?

[Kim-Ee Yeoh <yeoh@cs.wisc.edu>]

Hi,

I've just used the GP/Pari calculator for some polynomial algebra
experiments and would like to cite it in a paper I'm writing.  How do I go
about doing it?  Right now, my bibTeX entry (shown below) contains just
the user's guide, but it seems a shame not to include a URL as well for
people wanting to download the software.

@book{GPpari,
   author    = {C. Batut and K. Belabas and D. Bernardi and H. Cohen and M. Olivier},
   title     = {User's Guide to PARI-GP},
   publisher = {Laboratoire A2X, Universit\'e Bordeaux I, France},
   year      = 1998,
}

Would appreciate any advice on this issue.


-- Kim-Ee