OK, however using such an edge-colouring can increase the number of colours needed. e.g. 1-r-2 | | r b | | 3-b-1 | | w w | | 2-w-4 Jon Perry perry at globalnet.co.uk http://www.users.globalnet.co.uk/~perry/maths/ http://www.users.globalnet.co.uk/~perry/DIVMenu/ BrainBench MVP for HTML and JavaScript http://www.brainbench.com