Shitsudai
Table of contents | Table of diagrams Black first to kill Black first to live |
Shitsudai (失題, literally "missed problem"), is a Japanese term describing a composed tsumego (or problem) that has either no solutions or multiple solutions, i.e., the problem does not have a unique solution.
The equivalent term in Chinese is 失题 (shītí). However, there is currently no widely adopted English term for this concept. At present, just here in Sensei's Library, the term unsound has been used widely.
Uniqueness of the solution for tsumego
It is almost universally accepted that all tsumego should have a solution.^{[1]}
However, it is a part of Japanese Go culture that composed tsumego should not have multiple solutions. This is widely practiced by Japanese Go players, and they often label problems with multiple solutions as shitsudai in the problem description itself. This implies that such problems are defective, and where feasible they often modify the problem construction so that the modified problem has only one solution remaining. It should be noted that the presence of the shitsudai label does not mean that the problem is not worthy of discussion.
Outside of Japan, there is typically no requirement for composed tsumego to have only one solution, though at least some in China follow the Japanese convention as shown in "Examples" section below. It is also common for Chinese Go books that transliterate from Japanese sources to follow the Japanese convention and describe problems as 失题 (shītí), especially for classical Go problems such as Igo Hatsuyoron. In the English speaking Go community, the application of shitsudai or some similar label on problems with multiple solutions is controversial, with notable players and journalists such as John Fairbairn disagreeing with this practice and the notion that problems with multiple solutions are defective.
[1] Except for problems that ask for the status of the group in question, or instruct readers to prove that the group cannot live or be killed.
Definition of uniqueness
It can be quite subjective to exactly define what is meant by "uniqueness". One way to interpret "uniqueness" is that the problem contains only one main line. At the bare minimum, the first move of the solution should be unique.
Some reservations:
- For tsumego involving capturing races, the order of filling in liberties typically do not affect the "uniqueness" of the solution.
- Symmetrical problems that admit first moves on either side of the symmetry are not considered shitsudai.
- Meaningless forcing first moves are ignored.
Instructional value
Though multi-solution problems can be interesting on their own, the position is not critical enough if more than one move lead to success. One-solution problems are naturally better at sharpening your intuition in more critical positions where finding the only correct move is required. In addition, just looking at one-solution problems improves your intuition about how critical the situation is, even if you failed to solve. This is an indispensable ability in practice.
Single-solution problems are also more convenient to present. This could be useful in an instructional setting where students are drilled on a large number of problems involving a particular technique, without getting distracted by alternative valid solutions for some of the problems.
On the other hand, multi-solution problems allow the opportunity for solvers to find and evaluate the best possible solution. In addition, allowing problems to have multiple solutions more closely resembles the actual condition when playing games.
Examples of usage
1) This example is taken from here (blog by a part-time employee of the Nihon Kiin). The article describes the teacher (Mizuma Toshifumi) of being disappointed for presenting a problem that is shitsudai.
Black can kill by starting at either a or b, therefore this problem has two solutions and is shitsudai.
2) This example is taken from here (website of Eba Hiroki, author of Basic Life and Death Dictionary). On the page, the author apologized for posting a problem that is shitsudai.
Apart from starting with , Black can also live by starting with . Therefore, this problem is shitsudai with two solutions.
3) A popular Chinese site 101 Weiqi accepts user created problems and has a users' forum for discussions. Searching 失题 on the forum produces many results including 双解失题 (two-solution missed problem) and others.
4) Even some Chinese classic problems are described as 失题. This Chinese page explains a Go training software which includes a collection of 6,000 problems. The page says: "Xuan Xuan Qijing is a timeless classic, but it contains some shitsudai and wrong solutions." (《玄玄棋经》是一部不朽的名著，但其中也存在失题和错解。). The publisher omitted these shitsudai problems from the collection.
Other games
In other fields, there are many examples of the one-solution principle.
- In chess, it is an accepted modern practice that composed puzzles should have a unique first move. Puzzles with solutions other than the intended one are considered "cooked" or "unsound". Both "problems" (mate in # type) and "studies" (more practical type) follow the one-solution principle.
- Shogi puzzles, called tsumeshogi, also follow the same standard. A different word 不完全 fukanzen is used for the concept, which may well be a translation of "unsound".
- In sudoku, it is widely accepted that puzzles must have a unique solution. Therefore a sudoku puzzle must have a minimum of 17 givens. Players have derived techniques that exploit the uniqueness property, such as Bivalue Universal Grave.