School of Computer Science, The University of Manchester, UK. steve.pettifer@manchester.ac.uk|School of Computer Science, The University of Manchester, UK. steve.pettifer@manchester.ac.uk|School of Computer Science, The University of Manchester, UK. steve.pettifer@manchester.ac.uk|School of Computer Science, The University of Manchester, UK. steve.pettifer@manchester.ac.uk|School of Computer Science, The University of Manchester, UK. steve.pettifer@manchester.ac.uk|School of Computer Science, The University of Manchester, UK. steve.pettifer@manchester.ac.uk|School of Computer Science, The University of Manchester, UK. steve.pettifer@manchester.ac.uk|School of Computer Science, The University of Manchester, UK. steve.pettifer@manchester.ac.uk|School of Computer Science, The University of Manchester, UK. steve.pettifer@manchester.ac.uk