On Tue, Jun 19, 2018 at 12:03 PM, Marcel Crasmaru <crasma...@gmail.com> wrote: >> White can start one ladder as a ko threat to take back the middle ko, and >> black will then take the top ko.
> 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? Thanks for correcting me. You're right White can't use the ladders as ko threats. I also seem to have confused the formula expressed by the choice gadgets. If we call the three kos x,y,z from top to bottom, then a succesfull White ladder amounts to (x || y) && (y || z). Which is equivalent to y || (x && z). So with y currently false, and White unable to flip it, White should take the bottom ko to make z true. Black can the make x false, but that allows White to make y true, after which she can successfully escape in a ladder. regards, -John _______________________________________________ Computer-go mailing list Computer-go@computer-go.org http://computer-go.org/mailman/listinfo/computer-go
