Hmmm, a counter-example? 1-r-2 | | r r | | 3-r-4 | | b b | | 2-b-1 However: A o---o B |\ /| | / | |/ \| C o---o D |\ /| | X | |/ \| E o---o F needs 5 colours. 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