The final editing of the manuscript took place while Andrew Smith was on research leave from the University of Sheffield. He would like to thank colleagues on the school and faculty research committees for supporting this leave period. He would also like to thank, as always, Joanne Benson for her love and tolerance throughout the editing of this project.
William Hughes would like to thank John Strachan, Fiona Peters and Kevin Yuill for their valuable contribution to an earlier phase of this project. He would also like to thank Gillian for her constant love and support through difficult, as well as good, times.