* This author was partially supported by a Weizmann Fel-lowship and by the National Science Foundation under Grant No. DCR-86-0636. l l Also with the Department of Computer Science;
University of Warwick;
Coventry;
United Kingdom;
机构:
Univ Orange Free State, Dept Math & Appl Math, POB 339, ZA-9300 Bloemfontein, Free State, South AfricaUniv Orange Free State, Dept Math & Appl Math, POB 339, ZA-9300 Bloemfontein, Free State, South Africa