rst: The problem says no ko, no seki. How do you avoid ko with the move B T19 ?
If white plays P18 next, black needs to play either T18 or Q19 for it not to be seki.
B Q19 leads to W T18 which is alive.
B T18 leads to WQ18 which is only killable by ko via the sequence B S19, W T19.
What am I missing here?
caranthir: See https://senseis.xmp.net/?BentFourInTheCorner ------ With Chinese rules, you can postpone the ko sequence starting with A2 until you have removed all ko threats against you at the very end (after also filling all the point-scoring dame too, so it doesn't cost you anything), and therefore it follows that the shape is in effect dead. Conversely, according to Japanese rules, the shape is just dead by fiat (because removing ko threats against you would probably cost points).
See https://senseis.xmp.net/?BentFourInTheCorner ------ With Chinese rules, you can postpone the ko sequence starting with A2 until you have removed all ko threats against you at the very end (after also filling all the point-scoring dame too, so it doesn't cost you anything), and therefore it follows that the shape is in effect dead. Conversely, according to Japanese rules, the shape is just dead by fiat (because removing ko threats against you would probably cost points).