Deep invasion - example

In the game shown on the right it is White's turn to play. All the framework stones are stable and seemingly all the major boundaries are defined. It is time to count! The diagram shows a crude rendering of where territory (stones and spaces) should accrue. Where either side might acquire the intersection this is indicated by grey. White dominates 154 intersections and can anticipate acquiring roughly half of the 42 intermediate intersections giving a total of 175. But this is 6 short of the 181 needed to win. Given this narrow margin perhaps White should instigate a more accurate count, but for our purposes let us assume that this count errs on the side of optimism. How should White use this information?

Invasion?

White 1 is White's only hope of winning. If it doesn't work and White is a strong enough player to be certain of this, then, as a matter of etiquette, White might consider resignation. Putting matters of etiquette aside, the beauty of white 1 is that it can do no damage to White's cause. Because the frameworks are stable and because the invasion is deep i.e. not near a disputed boundary, White has everything to gain and nothing to lose. All the pressure is on Black to get his defence right! A number of responses might spring to mind but can you determine which of just two options A and B is best for Black?

Blunder!

After black 2 (option A) white 3 is atari upon the single black stone. Black 4 is forced because otherwise if White were to play there he would immediately gain an eye whilst simultaneously threatening to capture black 2. White 5 captures one stone and black 6 (atari) ensures that the captured intersection is turned into a false eye. However, what Black might not have anticipated is that White does not defend his stone but instead plays white 7. This ensures an eye at C and a ko for the second eye at D. Even if White does not "win" the ko, he might reasonably expect that Black will have to ignore a ko threat of a size that would allow him to win the game.

The correct response

If Black plays correctly White cannot win. The best response is black 2. This sets White one task too many. He hasn't enough room in the corner to make two eyes (legitimately) but it might seem that he could make one eye and connect at E to get the second. However, given correct play, all that is possible is for White to make one eye in the corner and fail to connect, or connect but fail to make the eye in the corner! Black of course could go wrong, so White might well consider continuing for a while longer. But if Black should lose he might justifiably feel robbed!