[1] UNIV CAMBRIDGE,DEPT PURE MATH,CAMBRIDGE,ENGLAND
[2] LOUISIANA STATE UNIV,DEPT MATH,BATON ROUGE,LA 70803
[3] UNIV LONDON BIRKBECK COLL,DEPT COMP SCI,LONDON WC1E 7HX,ENGLAND
[4] UNIV LONDON QUEEN MARY COLL,DEPT COMP SCI,LONDON E1 4NS,ENGLAND
[5] CARNEGIE MELLON UNIV,DEPT MATH,PITTSBURGH,PA 15213