Diagram 1 (1-32): (White plays 22 at 8, 26 at 17 and 28 at 15) White's moves of 2, 4 and 6 divide the board into two moyo. Yoda doesn't like that, so he plays at 7 to establish a position early on. The moves through 32 form a joseki (fixed corner exchange). White has thickness while Black has solid territory.
Problem 1: It is Black's turn. Black should try to move in his favor the line running from the upper right to the lower left corner that divides his moyo from White's. The positions A versus B and C versus D are mirror images. However, one position needs reinforcement more than the other--around the marked black stone that has the ability to cut off the marked white stones. Where should Black play?
Solution 1: Black 1 is the correct move. This is more important than A. If White were to play at A next, Black would still have a good chance to respond and invade the territory at or around B. Such a move would help his marked stone while attacking White's marked stones. But if Black played at A, White would build territory at 1. Since White's position would be strong on both sides, an invasion by Black at C would be dangerous.
Problem 2: Normally, white 34 is a good move. In this case, though, black 39--usually played at 40--is a better move. Black 43 captures 34 in a ladder. In addition, Black 45 takes advantage of White's mistake. Instead of white 44, White should have followed Reference 1.
After thinking for 55 minutes, White finally played at 46. Moving out with 47 to attack the marked white stones is very aggressive.
Note that Black has to keep the ladder of white 34 in check. Black's plan unfolds as he plays 53 through 67--effectively, he saves a stone by rendering white 34 useless without actually capturing the stone.
Meanwhile, White plays tesuji (a clever local move) at 64 to make 66 sente (a move that must be answered) and play hane (a diagonal block) at 68. Black 69 lays a heavy claim on the lower edge. White needs to settle himself with 70.
The problem is the next move. Let's assume Black's stones around 47 are not dead yet. Trying to rescue them seems dangerous. How can Black limit the damage while keeping White's upper side moyo in check? The solution will be carried next week.
Reference 1: White has time to play at 1 to expand his moyo. He doesn't need to add 3 until black 2. Black 4 is necessary to limit White's moyo and expand his own, again moving the territorial division line.
Solution to last week's problem
Solution 1A: If it were Black's turn, 1 and 3 would be excellent moves, pressing White's position down while building up his own moyo.
Solution 1B: On the other hand, if it were White's turn, he should play at 1. Locally, black 2 is a good move but after exchanging 3 for 4, Black's position still shows flaws at A or B. C may be best for White as his next move.
Van Zeijst is a four-time European go champion and European representative at the Fujitsu World Championship.