> Black can the make x false, but that allows White to make y true, after which > she can successfully escape in a ladder.
I think you are right and the solution is W takes at z, B is forced to take at x, W is forced to take at y and no matter what B does next W escapes from one of the ladders and makes the group alive. Now the question is how hard is to program a tsumego solver for this (kind of) problem. Cheers, Marcel On 19 June 2018 at 11:35, John Tromp <john.tr...@gmail.com> wrote: > 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 _______________________________________________ Computer-go mailing list Computer-go@computer-go.org http://computer-go.org/mailman/listinfo/computer-go
