Whatever our endeavors, ...
By Rob Van Zeijst
Whatever our endeavors, interests or possessions, we generally measure them against those of others, using a variety of tools, such as spectrometers, clocks, scoring systems, IQ tests and money. These yardsticks allow us to satisfy ourselves that our car is better than our neighbor's, or we wager that our favorite sports team will beat the pants off the competition.
In go, we use points for comparison, but we can only use them for counting concrete situations or to measure the final score. However, what about new patterns or unknown situations? Pros use a tool called tewari to compare new situations to old ones in order to make a meaningful evaluation.
Let's use tewari to evaluate the following game, the first game of the 61st Honinbo title match in which Kimio Yamada challenges first time defender Shinji Takao (White).
Diagram 1 (1-35): With 11, Black initiates hostilities. This move is a new kind of play and gives rise to the sequence through 24, leading to a very unusual pattern. As a result, we cannot make historical comparisons. How shall we evaluate this situation? See the analysis in Diagrams 2-4.
Tewari
Tewari is used to evaluate a situation when counting points does not work. It is a tool where the order of the moves may be changed and stones removed to enable comparison to a known position.
Diagram 2: Notice that White has used two stones more than Black. Therefore, the result on the left side is not even. Now let us see how we got to this position by reversing moves so we can arrive at a common position. The moves through 8 are a joseki. However, black 9 is not. Instead, let's say Black plays at A or B. The exchange 10 for 11 and 12 for 13 are slightly disadvantageous for White. Black 15 is not a move that has to be played at this time, but it is not worthless. On the other hand, white 14 is a good move but white 16 seems a little slow. In short, we have to evaluate the 15 for 16 exchange. This is slightly favorable for White. However, the analysis does not end there.
Diagram 3: At this point, there are three important points, around 1, around 4 and at 5. In the game, 1 through 5 are played, meaning Black gets two out of the three good points. On top of that, the marked black stone is ideally positioned to limit White's thickness on the lower side. This is why most pros following the game thought Black had no reason to be dissatisfied.
Diagram 4: For some, not answering black A is inconceivable. What happens when White plays elsewhere? Black plays at 1 and 3, while White makes a base with 2 and 4. Instead of 4, White can also play at A, or in special cases at B or C.
Diagram 5: When Black has a stone at 3-3, extending to 1 is a possible follow-up. To reduce the corner, White 2 through 6 are a standard method. This gives the same result as Diagram 4 with a different order of moves. The only thing White should be afraid of is if Black plays at 5 at A, but this is true for Diagram 4, too.
Solution to last week's problem
Solution 1A: The sequence through 11 is a joseki-a standard corner exchange, which is considered even.
Reference 1: The problem posed last week is analogous to the result through 13. For Black, this is inferior to Solution 1A, because he jumped to 13 one move late. Therefore, tewari and comparing this to Solution 1A tell us there is something wrong with this diagram.
Solution 1B: That is why after 6, Black must not play at B. Instead, 7 is the vital point to attack White's eye-shape. White can now follow up with A or B, but either way, he does not get a good result. Therefore, white 6 can be viewed as a trick move.
New Problem:
Problem 1: The moves through 5 are a standard sequence. In the past few years, many joseki have been questioned, giving rise to new moves. One development was to play at 6 before playing hane (diagonal connecting move) at 8. How should Black answer this move?
Reference 2: The normal order would be to play hane at 6, Black would extend to 7 and White would invade at 8. The sequence through 11 follows. Note that Black does not block at 10 when White invades at 8.
Van Zeijst is a four-time European go champion and European representative at the Fujitsu World Championship.