> White can start one ladder as a ko threat to take back the middle ko, and > black will then take the top ko.
Thank you John for verifying the problem! I claim that White cannot use the ladders as a ko thread because: - if W plays R4 as a ko threat then B responds with S4 - if next W takes a ko back on the board then B kills the group locally by playing S6: the left ladder is no longer a ladder and if W gets out of the right ladder then the bottom W group ends in 2 liberties and B can capture it Is the above reasoning sound? --Marcel On 19 June 2018 at 08:52, John Tromp <john.tr...@gmail.com> wrote: > On Tue, Jun 19, 2018 at 3:52 AM, Marcel Crasmaru <crasma...@gmail.com> wrote: >> I've eventually managed to create a problem that should show a full >> reduction from a Robson problem to Go - I hope is correct. >> >> The Problem: >> https://drive.google.com/file/d/1tmClDIs-baXUqRC7fQ2iKzMRXoQuGmz2/view?usp=sharing >> Black just captured in the marked ko. How should White play to save >> the lower group? > > It looks like White needs to hold the middle ko and either top or > bottom ko to make the ladders work. > White can start one ladder as a ko threat to take back the middle ko, > and black will then take the top ko. > Now if white (possibly using another ladder ko threat) takes back > either top or bottom ko, Black can retake > the middle one and White has made no progress. So it looks like White > is doomed?! > > regards, > -John > _______________________________________________ > Computer-go mailing list > Computer-go@computer-go.org > http://computer-go.org/mailman/listinfo/computer-go _______________________________________________ Computer-go mailing list Computer-go@computer-go.org http://computer-go.org/mailman/listinfo/computer-go
