DavidBird

The articles that Taf Anthias and I wrote for Bridge Magazine (one of which was reprinted in a Poznan bulletin) are part of a 200-page book to be published by Master Point. In that book we address some of the subjects that BBO members have mentioned in this discussion. We are fully aware that double-dummy simulation has a few side effects, such as saving declarer a guess when you lead the king from K-Q-x-x-x. This is an excerpt from the book that covers it: How often does an honor lead save declarer a guess? Our double-dummy simulations suggest that it is profitable to lead from touching honors more often than traditional text-books imply. Occasionally the lead of a king from such as sxK-Q-6-5-2 will save declarer a guess. Look at this single-suit position, for example: ..... sx J 9 4 sx K Q 6 5 2 ..... sx 10 8 ..... sx A 7 3 If you lead low against a real-life declarer, he may play dummy’s sx9, which will create a second trick for him when your spades are headed by the K-10 or the Q-10. The defenders can then establish four tricks in the suit. (A low lead would not succeed at double-dummy because the all-seeing computer declarer would rise with dummy’s jack.) If instead you lead the king, declarer can place you with the K-Q and will score two tricks in the suit. This sort of position may throw some doubt on the validity of using double-dummy simulation, so we have taken some trouble to evaluate how often these ‘save declarer a guess’ positions arise. We have written software that analyzes the frequency of the various honor positions for North/South on one of our 5000-deal simulations. Look back at Hand 9, where the sxK lead was rated best from sxK-Q-6-5-2. How often would such a lead have saved declarer a guess in the suit? These are the figures from our profile: North South Probability A J 9 ..... x x (+) ..... 0.36% A J x ..... 9 x (+) ..... 0.54% J 9 x ..... A x (+) ..... 1.44% J x x ..... A 9 (+) ..... 1.20% Leading the king will save declarer a guess in the suit on 3.54% of the deals. Does this wipe out the 3.2% advantage awarded to the sxK lead in our table for on Hand 8, above? No, because on many of the deals the contract would be made, however declarer plays the spade suit. Also, on some deals declarer cannot afford to lose a trick in spades (because he fears a switch to some different suit); he might then play dummy’s jack even after a low lead. So, we have ‘come clean’ on this aspect of double-dummy simulation. There is a similar effect when you lead a top card from A-K-x-x-x. This may save declarer a guess when dummy has Q-10-x, or the Q-x-x in dummy with the 10 in declarer’s hand. When you lead an honor from Q-J-x-x-x, you may find dummy with K-10-x and declarer with A-8-x. Whenever our simulation results recommend an honor lead from touching honors, you can mentally subtract a percentage point or two from the ratings, to allow for the effects against a living, breathing declarer. END OF EXCERPT Another member's comment referred to the fact that if you lead king for unblock-or-count against no-trump contracts, you cannot do the same from K-Q-x-x. Yes, but all players who use this method are familiar already with leading the queen when they do not want unblock-or-count. 'Ace for attitude, king for count' embeds also 'queen for attitude'. The fact that players may now lead an honor from K-Q-x-x has no bearing on the matter. (In the US they tend to lead the ace to pass the unblock-or-count message and therefore lead the K from A-K when they do not want an unblock.)