Six point double sente diagonal
In a game we will often encounter situations which, abstracted, are like this diagram. To the left is some white territory, to the right is some black territory. is now a big endgame move. It is commonly called a "six point double sente". Obviously the discussion is symmetric for there.
Let's assume answers. Then later, - is a typical hane connect endgame move, where we also assume that is necessary (i.e. otherwise Black can cut and there are no white stones to which can run). Even later, it is White's prerequisite to play and Black will cover at .
If White were to execute the symmetric
sequence, the marked points would not be black territory, while the points at , and would. The net difference is therefore 6 points.
A much harder question to answer is whether these moves are really sente. Clearly, in this abstracted situation, Black can jump in at and nearly all visible white territory is destroyed.
- how much territory will be destroyed beyond what's visible here
- can White therefore even allow for another move here (because there is not so much to destroy afterwards)
- or is, quite the contrary, the life of her surrounding stones at stake
- how well is the concrete situation still represented by the abstract situation here
- and how about mutual damage
These questions are discussed at the following pages:
If indeed the moves are sente for both, the value is 6 points. However, professionals will rarely allow a situation to become double sente. Database search suggests that in fact pros answer this move half of the time. In the other half, it is not certain that the symmetrical move would also be answered.
- Lee Sedol - Gu Li jubango, game 4, discussion at move 76.