The carpenter's square is unsettled. is the vital point, making it unconditionally alive.
If Black wins the ko, he will resolve it by capturing and
, Black can later reduce white left edge territory in sente. Thus this ko is worse for white.
A refutation (why can't be at
) - killing by nakade, the number of black's outside liberties doesn't matter
If Black wins the ko he has a sente endgame on the upper side and a bigger corner than in original ko n°1.
White needs two moves to almost fill the corner and in this process she can't make a dead 6-point-shape inside so this ends in seki. This seki usually is even worse for white than the above ko. (If white wants a seki, she can make a better one by deviating with from the normal ko n°1 line.)
If Black wins the ko, he'll resolve it by capturing and
. He can further reduce white along both sides in sente.
White can't answer with a because this ends in double ko life for Black. But if White hasn't enough threats left, she can still settle for a - with the double ko life giving an infinite amount of ko threats for White / later two moves in a row if Black is finally going to resolve it. Thus this is a lot better for White. (I'm not sure about the ko with
at b)
connecting is wrong, White wins the eye-vs-non-eye semeai
at
(changing move order) does not change the result.
After Black is dead (LeatherScrollProblem144/Solution)
If connects out, black is dead, if white can fill with dead shape + eye (so that it can not be seki) it is dead. So actually there is no way to live.
This is no dead shape, but white wins the eye vs. non-eye semeai with 3 vs. 2 effective liberties. This line is sensitive to outside liberties and doesn't work with black outside liberties.
While f and g are obvious failures - e.g. after a black answer at the vital 2-2 point - d and e merit some discussion. CarpentersSquareWrongAttack discusses e (against which Black stretches for at least seki) in detail.
This is pretty similar to a first move at e - with the additional (and bad) exchange of for
, which disables the seki lines.
The refutation of at
see above, doesn't work with outside liberties, the refutation of
at
as well... so everything changes. (below diagrams to be changed).
Black can't avoid ko, if he tries with this , he dies by nakade. If not, he has just another ko. But this ko may be worse for white in the endgame if she loses the ko since
is in place already.