Backgammon

THIS WAS the final and the most difficult question in this year's Christmas Quiz. Black on roll, should he double - and if doubled, should white take?

This is a strange position, where black is in fact better off staying on the bar than entering - unless, of course, he enters with 61. Certainly, when black enters with a number such as 15, white does have considerable winning chances.

In any event, white has good chances. He has a three-point holding game and black has yet to make his own four-point, the lack of which will make his bear-in quite difficult. It is surprising how often this type of position generates shots for the defending side.

I have spent hours rolling out this position, both manually and with my silicon friends, Snowie and Jellyfish. I am now comfortable that I understand the dynamics involved. Whenever black fails to enter and white doesn't roll 11, 21 or 61, then black has a double that white must drop. Thus the position is highly volatile. Black must double now or risk losing his market by the next roll.

White can generate enough winning chances from black's immediate bad entering numbers plus the equity he gets from his three-point holding game to give him a fairly comfortable take. So the quiz answer is double/take.

This position in fact occurred in the 1998 world championship match between Elliot Winslow and Michael Meyburg.

Winslow, trailing 18-20 in a match to 25, doubled and Meyburg passed. As often happens towards the end of big matches, players handle the cube conservatively. Meyburg probably feared a gammon loss if things went badly and was content to maintain a small lead. He should have taken.

Chris Bray can be contacted on bray@ globalnet.co.uk