here is a tsumego that I saw during a 5d (blitz ^^) game on kgs
none of the player added any stones to protect against it: they pretty much ignored the position.
whole board now ^^
So, the ugly black group on the left seems (to me) killable. What would have happenend had white played the marked stone ? there are lots of differents endings, but I'm not sure of the best line of play (I'll bet seki or Black dead)
What do you think ?
Herman Hiddema: Here's a line of play. is the key move. If white defends the cut at , black can play at and live. If white does not defend the cut, but plays , then after and , black can cut in sente. After the throw in of and , black plays and white is unable to connect due to damezumari. Thus black captures three and makes an eye, with another eye at a.
atulab: cant w play 10 at b ? thus destroying black's second eye. I think this leads to a double ko but I think white can actually win it.
fractic: If white plays , to destroy the eye (black can't play a), then black plays white at the circled stone. Black now exchanges for .
fractic: If black now plays at then can try and kill. It looks like double ko but it isn't. The best I can find for black is the sequence up to . White then takes the ko and black needs a huge ko-threat.
fractic: But black has a better play at getting a seki.
Jeff: Black's dead, imho. If black doesn't take , white does, again resulting in only one eye for black. To live, black would need to skip and instead kill the marked white stones. But I can't read a way for black to stand a chance -- white escapes to the center in every variation I tried.
Herman Hiddema: black should play first, the marked stone was the intended killing move.