Sending three returning two
Herman: Adapted from a recent game of mine.
With Black to move, the position in the upper left seems hopeless. If white captures all of black's stones, white will win (black is ahead by 1 point on the board, so white's komi will be decisive)
is necessary. If white plays a, black plays at
and the position will be seki, so white will lose.
After , a cycle of length five has occurred (compare the first diagram). white has no move now, but if white passes, then black can pass and under some rules a dispute may occur.
If white does play a move (costing a point), then black will repeat the cycle. This can continue until there are no more viable moves for white. At which point white will be forced to pass.
Note that black will never have time to play a, because he must force the cycle or lose the fight.
The position has some similarity to moonshine life.
Discussion
unkx80: Interesting position. Under certain rules such as superko rules, isn't prohibited?
ThorAvaTahr: see cycle, the position fits the cycle of five herman has been looking for. Actually regardless the rule set white will win in this position since there are no ko-threats, even if the cycle was allowed it costs one point every time he carries out the cycle. IMO you can promote this position to the cycle page, I can find no flaw. Nice job!
Bill: Very nice position! :) Different rules treat this differently.
Under AGA rules and New Zealand rules Black can repeat the position because it does not repeat the situation, as the player to move is different. Then after White's pass Black can pass, ending play.
Under Ing rules I think that this would be deemed a disturbing ko, and White could eventually take the Black stones.
Under Japanese rules things get interesting. ;)
Taking this as the final position, the stones are dead, because White can capture them in ko. The
stones are also dead.
The scoring is interesting. Because of the two dame () in the top left corner, the adjacent White stones are in seki, and so the dead Black stones cannot be removed. (Dead stones can only be removed from territory.) The same goes for the dead White stones in the bottom right corner. The main Black stones are also in seki. The Japanese rules are not all that clear about what it means for a stone to have dame, and thus be in seki, as some stones that are not adjacent to neutral points are said to be in seki. I think that the correct interpretation is that all of the stones on the board are in seki, except the White group in the top right. (See the Spight Japanese style rules for my interpretation.) White has 3 points of territory and has captured 3 stones and Black has captured 2 stones, so White is ahead by 4 points plus komi, if any.
Under Spight Japanese style rules Black can play sending three returning two to repeat the position and then White passes, then if Black repeats the position again the round ends and play stops. Then play starts again in the encore with White to play without any ko ban. So White can take the ko.