Andrew Butterfield holds an honours degree in Engineering and a PhD in Computer Science and is currently Head of the Foundation and Methods Group at Trinity College Dublin, as well as Director of Undergraduate Teaching and Learning in the School of Computer Science and Statistics. His research interests include the formal aspects of computing and pure lazy functional programming languages, and he has published in various specialist journals (Formal Aspects ofComputing, Science of Programming), has edited a number of conference proceedings (Implementing Functional Languages, Unifying Theories of Programming) and has been guest editor for an issue of Formal Methods in System Design.Gerard Ekembe Ngondi holds a Bachelor of Engineering degree in Telecommunications obtained at the National Advanced School of Post and Telecommunications (Yaounde, Cameroon) and an MSc in Computing obtained at the University of York (UK). He is currently doing a PhD in Computer Science at the University of York. His research work is on formal reasoning about the concept of 'mobility' in the UTP (Unifying Theories of Programming) framework. Less