abstract appeared in: Proc. of 7th Ann. Int. Computing and Combinatorics Conference, COCOON 2001 (ed. J. Wang), Lecture Notes in Computer Science Vol. 2108, Springer-Verlag, Berlin (2001) 39-48. Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-profit purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full DRO policy for further details. Durham University Library, Stockton Road, Durham DH1 3LY, United Kingdom Tel : +44 (0)191 334 3042 — Fax : +44 (0)191 334 2971 http://dro.dur.ac.uk
Iain A. Stewart