![]() StartingPoints Paths
|
Lopsided Kos
Path: KoFighting · Prev: KoThreatPlayingOrder · Next: FindingAKo
Difficulty: Beginner
Keywords: Ko
Not all kos are worth the same to both sides; in the BasicKoFight example, white had nothing to lose by playing the ko, so she need not have any qualms starting it. However, some kos can cost more then they are worth. Imagine a situation like the one here.
Here, if white starts the ko with 'a', but then loses the ko eventually, she will lose her lower right corner. If black loses the ko, then he will lose his group at the lower edge. Hence, the ko at 'a' and 'b' is important for white as well. In this situation white needs ko threats larger than her corner in order to win the ko. It would be of no use for her to play a ko threat of e.g. 10 points, as her corner is worth at least 15 points. Black would finish the ko by playing 'c' and would have gained 5 points or more. Comment: I have calculated the values of these positions (ignoring the ko threats on the left and assuming that the right side is Black territory). They are hyperactive, which means that their value depends on who can win the ko. Who can win the ko is called the komaster. I have not included Black's territory on the right. If Black is komaster, White connects with sente. The local result is -1 (1 point for White, net). If White is komaster, the miai value of the position is 12 1/3. Either Black connects or White throws in. The local count is -2 1/3. There is a new technique for evaluating kos, based on the idea that nobody is komaster, but one player can win the ko while the other gets an equitable exchange. That method gives a local count of -1, but Black connects with sente.
This diagram is different. Here white has the marked stone in place and thus losing the ko for her means only losing the single stone at the edge. Black on the other hand may lose his group worth over 20 points. If white plays a ko threat worth 10 points in this situation, black will finish the ko as well (again playing 'c'), but this time white will be better off. She would gain 4 points compared to connecting at 'b' instead. Comment: The ko, once made, has a miai value of 10 1/3, and that is the size of equitable threats for it at that ambient temperature. (The ambient temperature is the size of the largest plays elsewhere.) If Black is komaster, White starts the ko, losing it in exchange for plays elsewhere, when the ambient temperature is between 5 and 10 1/3, as a rule. Below that temperature White connects with sente. The local count is -6 1/3. If White is komaster, either Black fills at 'a' or White throws in. The miai value of a play at 'a' is 9. The local count is -9. By the no komaster method, the local count lies in between, at -7 2/3. -- BillSpight The importance of this difference is the following: If a ko is 'lopsided' in your advantage, you should have no qualms to start it. You might well lose the ko, but you will get an unanswered ko threat in compensation. Thus, in the second diagram on this page, white should (if the ko is large enough) almost alway play at 'a' if it is her move, and be happy whether she wins or loses the ko. In the first diagram on the other hand, she will have to count both players' ko threats first. If black has more (sufficiently large ko threats, it is best to play 'b'. If white has more, 'a' is better. On the other hand, if it is black's move, he should never (well, almost never) play the ko in the second diagram, but connect at 'a' instead. In the first diagram, his choice too hangs on the balance of ko threats. Authors:
Path: KoFighting · Prev: KoThreatPlayingOrder · Next: FindingAKo This is a copy of the living page "Lopsided Kos" at Sensei's Library. (C) the Authors, published under the OpenContent License V1.0. |