David Walker (Robert Hill Institute, U.of Sheffield, U.K.) Anyone wishing to reach me at home please use 9,Canterbury Crescent,Sheffield S10 3RW, U.K (mail forwarded by kind neighbours when I am in depths of darkest Northumberland) phone OR fax +44 114 2305904 (calls forwarded by British Telecom) Email David at alegba.demon.co.uk (I take my modem with me)