very close (with your reasoning) -- but I wouldn't call it "giving up" on black's a4 stone.

You're actually sacrificing it for something much larger. And you won't have to give up the corner at all -- do you see it yet? That's why white will not cut at (b). You can count on it. But you need to see what happens if they do, how black can punish.

I am no good at playing against myself, but after Black's a7, White cannot connect at the top, and I do not see enough space left in the bottom-left for White to create a living group.

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Regards,

Peter

Peter,That is exactly what people do when we want to improve: improve our reading.

me neither. I always hate it when I lose to myself.