ninestone wrote:I saw that it's ko. There are no threats for white so the only response is to connect at E4.
Not so, as I shall show below.
Maybe I just have an aversion to calling the solution wrong just because it's not exactly what the author wanted.
Oh, go players are quite aware that a problem may have multiple solutions. That is not the case here. There is only one solution.
And capturing 5 stones is optimistic when white can connect after the peep (that's another solution GoChild accepts).
It's not another solution, it's another variation. For Black to have a solution, it has to work for
every reply White could make. In fact, capturing the 5 stones is the key variation because Black has to see the tesuji combination of throwing away three stones to reduce White's liberties. GoChild should not really accept a solution that does not include that variation. (IMO, it should not accept a solution without both variations.) In real life, White should not choose that variation, but this is a problem for Black, not White.
WHy is ko not a solution? First, because it is unsure. If there is a sure way to kill or live or connect or cut, ko is not the solution. (Sometimes double ko is the solution, if it provides a sure way.) One reason for that is that you may lose the ko in real life. The problem does not show the whole board, so we do not know the ko threat situation. (Oh, looking at the diagram, perhaps GoChild shows the whole board. It should not. If this were the whole board, Black could resign.
) Let me illustrate the other reason below.
$$Bc Real life variation
$$ ----------------------------
$$ | . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . |
$$ | . . . , . . , . . , . . . |
$$ | . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . |
$$ | . . . , . . , . . , . . . |
$$ | . . O O . . . . . . . . . |
$$ | . O . . O . . . . . . . . |
$$ | . . O O 4 O O O O O O . . |
$$ | X X X X O X X X X X O . . |
$$ | . . X O 2 O X . . X O . . |
$$ | . . X 5 1 3 . . . X . . . |
$$ ---------------------------
- Click Here To Show Diagram Code
[go]$$Bc Real life variation
$$ ----------------------------
$$ | . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . |
$$ | . . . , . . , . . , . . . |
$$ | . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . |
$$ | . . . , . . , . . , . . . |
$$ | . . O O . . . . . . . . . |
$$ | . O . . O . . . . . . . . |
$$ | . . O O 4 O O O O O O . . |
$$ | X X X X O X X X X X O . . |
$$ | . . X O 2 O X . . X O . . |
$$ | . . X 5 1 3 . . . X . . . |
$$ ---------------------------[/go]
connects. White can save
and
as ko threats.
$$Bc Ko
$$ ----------------------------
$$ | . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . |
$$ | . . . , . . , . . , . . . |
$$ | . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . |
$$ | . . . , . . , . . , . . . |
$$ | . . O O . . . . . . . . . |
$$ | . O . . O . . . . . . . . |
$$ | . . O O . O O O O O O . . |
$$ | X X X X O X X X X X O . . |
$$ | . . X O 3 O X . . X O . . |
$$ | . . X 5 2 1 . . . X . . . |
$$ ---------------------------
- Click Here To Show Diagram Code
[go]$$Bc Ko
$$ ----------------------------
$$ | . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . |
$$ | . . . , . . , . . , . . . |
$$ | . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . |
$$ | . . . , . . , . . , . . . |
$$ | . . O O . . . . . . . . . |
$$ | . O . . O . . . . . . . . |
$$ | . . O O . O O O O O O . . |
$$ | X X X X O X X X X X O . . |
$$ | . . X O 3 O X . . X O . . |
$$ | . . X 5 2 1 . . . X . . . |
$$ ---------------------------[/go]
elsewhere
is the correct response (almost regardless of the rest of the board) to
. The ko is humungous, and in real life White will not have a ko threat that Black should answer. But White should make the ko, anyway. Making the ko forces Black to make two net plays to connect instead of one. White sacrifices a few stones for an extra play somewhere else. (It is conceivable that there will be no play big enough elsewhere for White to make that sacrifice. However, the possibility that there is is enough for
not to be part of the solution when Black has a sure connection in one net play.)
at E2 strikes me as a perfectly valid solution. What am I not seeing?