Moved from L-group/Discussion:
Srki: Ogawa Tomoko says that in diagram below was worth sixteen points. How? Can someone explain?
Chris Hayashida: Calculating the endgame can be confusing. It's easiest to look at the basic situation with each player getting to move first.
Chris Hayashida: First, let's say Black gets to move first. This is how he will play, ending in gote.
Chris Hayashida: This is the tricky part. White won't play a right away, because it's gote. (Technically, it's reverse sente, but don't worry about that for now.) White will probably play somewhere else on the board instead.
Chris Hayashida: Eventually, Black will get around to playing the sequence starting with .
Chris Hayashida: Now let's calculate if White gets first move.
Chris Hayashida: In a similar vein, Black won't play a immediately. There are still bigger moves on the board.
Chris Hayashida: Eventually, White will get the sequence starting with .
- Black 5 points
- White 13 points + 1 prisoner
Chris Hayashida: As you can see, the first diagram has B+7, and the second has W+9. It's a sixteen point swing.
Chris Hayashida: The problem with this line of play is that there is ko. I think White is trying to avoid ko. Note that this is *calculation* so this is (in part) why White is trying to read ahead the safer variation.
Srki: Chris, thank you very much, this was very helpful. Everything is clear now.
This isn't even ko. If white plays captures after , black will play and white cannot defend the double atari because the all the white stones are captured at a. If white plays at instead of , black plays a immediately and the result will be equally devastating.
Note that White does not have this sente if Black captures the stones.
Bill: Next, is larger than . After , - is sente.
Bill: If - , Black continues with - , which is sente. The corner is small by comparison.
Because the surroundings are not shown, we do not really know how much a play is worth here. But we do know that the left side and the top side are not independent, and that the play on the left is therefore worth more than 16 points (deiri counting).
Ogawa qualified her remarks, with the sente above in mind: "The time had come to capture at ( in this diagram). In terms of the left edge alone, this move was worth sixteen points. It gave White additional profit on the upper edge by making White a ( in this diagram) sente."
Anyway, in these undefined situations, such calculations are only rough indications.