Julian Bradfield
Computer Science, The University of Edinburgh,
Kings' Buildings,
Mayfield Road, Edinburgh, EH9 3JZ, UK
jcb@dcs.ed.ac.uk

Colin Stirling
Laboratory for Foundations of Computer Science,
School of Informatics, The University of Edinburgh,
Mayfield Road, Edinburgh, EH9 3JZ, UK
cps@inf.ed.ac.uk