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11

Molasses ko: http://denisfeldmann.fr/bestiary3.htm#mol "The semeai in figure 11 is probably the worst known case of repetition. Known as "molasses ko", ..." Denis Feldmann's Go Bestiary is a compendium of various things (interresting semeai, life and death, edge cases, incredible problems, rules edge cases, weird sekis, etc).


10

I think the easiest way to think of this is in terms of options, and the freedom to take whatever options benefit me. In your example, you have no options: You need to win this ko, or you will lose. However, in my case, killing you might not be my only option. I could kill you and swing things thirty points in my favor, or if I felt like it I could grab ...


9

In all official rules that I know this means instant forfeit of the game. Of course, in casual play, mistakes like this can be allowed to take back at the will of the players. In tournaments I would strongly advise against making such a mistake as well as trying to ask for a take back. If the other player does not seem to allow a take back by his own active ...


8

No, this logic unfortunately doesn't work: It prevents moves that are in fact legal, because they include a snapback. $$ white to play $$ . . . . . . . $$ . . X O X . . $$ . X O X . X . $$ . X O O O X . $$ . . X X X . . $$ . . . . . . . White captures: $$W $$ . . . . . . . $$ . . X O X . . $$ . X O a 1 X . $$ . X O O O X . $$ . . X X X . . $$ . . . . . . ....


7

At least in European tournaments current rule is that if you play an illegal move you have to take it back, and play a legal move. You don't lose the game by default. Illegal move If a player makes an illegal move, and if this is noticed within three moves, then the game should be unwound to the move just before the illegal move, and continued. The referee ...


6

Ko only prevents a player from making a move that would have the effect of returning the board to the position that it was in just before his opponent's last move only. So the only thing you ever need to keep track of is what the board was like just before your opponent made his last move; you cannot move such that it would recreate that position. All the ...


5

One important point to understand is that in an amateur tournament, whenever both players agree on something, then it's ok. For example, if one player plays an illegal move (like taking back a ko immediately) and the other says "take back your move and let's pretend nothing happened", then so it is: nothing happened. Problems only occur when the players ...


4

"Ko" is effectively one of those situations where you can hope to get two moves in a row (e.g. if your opponent spends his next move filling, or otherwise removing the ko). On the other hand, if your opponent chooses to allow you this, it means that the value of the ko is large. (Otherwise he would answer your ko threat and ignore the ko). Balancing the ...


3

There is a difference between the two semi-stable double ko positions, although a rather small one. C14 reduces the immediate number of liberties of the G13 leg. This means that black will have a free tempo when G13 runs out of liberties, if we assume that black can find a big enough ko threat to answer the C13 capture with C14 in order to force the B15 gote....


3

Yes, that's the best you can do.


2

The theoretical answer depends whose rules you are using, because different countries use different rules, and have different ways of dealing with the multi-ko1 situation you describe. In practice this almost never arises, and keeping track is usually easy, as something else happens to change the whole-board state, such as a move on a previously unoccupied ...


2

Super Ko can be detected efficiently using Zobrist hashing. https://en.wikipedia.org/wiki/Zobrist_hashing https://www.gnu.org/software/gnugo/gnugo_11.html#SEC144 The idea is to pick a random 64-bit integer to represent each of the 2x19x19 = 722 positions on the board. The empty board has a hash value of 0. When you add a stone to the board you XOR the ...


2

I would say the added dimension comes from the "long-range" nature of kos. It is possible, through a ko, for two, otherwise loosely linked regions to be directly compared. Each ko evaluates the entire board in the context of the local position. In that sense, it creates considerable added complexity to a game.


2

Your rule is adequate to detect simple kos but not all forbidden repetitions. EDIT: It incorrectly forbids snapbacks, as observed in balpha’s answer, and thus fails your condition (2). It is unclear to me from your question whether the “moves that would illegally recapture a ko” that you want it to prevent include only immediate recaptures or also later ...


1

Short answer How can a ko fight be “asymmetric”? By offering one player a strong incentive to start it. When a ko is asymmetric You are right that once the ko is started, the result is equally valuable to both sides. Where the asymmetry comes in is when one player, considering whether to start the ko, compares three local outcomes: They start the ko and ...


1

You need something like three kos to do this. But let's say that there are two players, X and Y. Player X takes the first ko. Player Y takes a second ko as a "ko threat." Player X takes a third ko in response. Player Y re-takes the first ko. Etc. The ko rule serves to prevent repetition between one or two kos. But if there are enough kos so that you can ...


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