I'm sorta embarrassed to post this, since I must be missing something really trivial. But I couldn't find it, nor could MFoG.

The text says "Black plays the hane at 209 (G19), White blocks, and Black connects. White protects at 212."

Why can't white protect at E16 (B in my diagram)? And what can black actually do if white plays somewhere else and doesn't protect at all? I'm not finding any branch where B can get even one point by playing first in that area.

Why can't white just play at E16 or K19?

Partial board:

Hi Milkman,

Good question.

If W plays at your (B) instead of (A), study the final shape at the end of the game,
after both of W's outside liberties (E15 and G15) are filled.

This is a good exercise for both your reading and shape recognition.

Ah, black E18, right? Sigh. But that's after white's group is closed in. Why does white need to do this right away, instead of playing elsewhere and waiting for black G15 and E16? Can black reduce white at all *before* surrounding the group?

Yes, E18.

To answer your question about the correct yose move,
it helps to see the entire board.

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

Just to make it clear, as bill points out this move is one point in reverse sente. I am assuming it is close to the end of the game and there are no bigger moves on the board. At this point of the game a one point reverse sente move can be quite big, certainly bigger than a one point gote move. There may be an even number of two point double gote moves which, on the surface appear bigger, but they would be considered miai.

_________________
Still officially AGA 5d but I play so irregularly these days that I am probably only 3d or 4d over the board (but hopefully still 5d in terms of knowledge, theory and the ability to contribute).

as others have pointed out, this is an excellent question... here's how I like to explain it (though I don't know if it'll be any clearer or not)...

While white e16 looks, at first, as if its going to give you an extra point, it doesn't because of the eventual threat of black e18. White will have to play at least one more move on the inside to protect against that threat -- thus losing that point you thought you gained.

So, playing white e17 now, doesn't change the score (since you won't get that extra point anyway), and it takes away the threat.

Taking away the threat is big, because if black gets to push white around in sente later, he could possibly gain even more himself. Not to mention, if black gets an opportunity to actually play that threat (since you wanted to wait until later to protect against it), you could potentially lose even more.

Summary... its a strong shape leaving no weakness to attack, and there is no point there to be gained.

This is the game in question. Could white play at B213 instead of protecting at 212? I'm not good enough to make the last 28 moves, since changing the order will affect the outcome, right? I'm running a simulation now but it'll take time.

Thank you all for your comments. It is certainly much clearer. I guess the phrasing in the book made me think W212 was an immediate protection for some local black attack.

I am guessing that this was a pro game from the late 20th century. In byoyomi if pros can read out a win, they tend to go with that. I think that your suspicion is correct, that White could have won by more than 3.5 points. I have put what I think is better play in a variation at move 212.



Edit: Found what may be a slight improvement for Black in the variation.

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

Thanks, Bill! What is the meaning of B221 at A10 in your variation? Is it because black cannot win the ko that'd result if White A10?

Well, I have since revised that variation. That particular ko is tricky, because at first glance it looks like each player has a threat to win the ko that is larger than taking the ko. Black can guard against a White throw-in at A-10, followed by Black connection at B-11, followed by a White connection at A-09, by playing A-10 himself, either with sente or with a sente follow-up. The difference is typically small. Similarly, White could guard against a Black throw-in at A-09, followed by a White connection at B-08, followed by a Black connection at A-10, by playing at A-09. White's throw-in is more dangerous, which is why I think that Black will normally play A-10. In the actual game neither player threw in, and that is frequently how play will go.

In the revised variation, the ko on the top side is a sente ko for Black, which he will typically win. And that is what I showed.

I could have spent time trying to analyze the different ko fights, but both sides have a number of ko threats, and it is a secondary question. In any event, I think that with White 212 in the variation White should win by 4.5 points, maybe by 5.5.

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.