Conventions in Life and Death

    Keywords: Life & Death

It has been suggested that the content of this page should be merged with Tsumego Conventions.


The assumptions in life-and-death (tsumego) problems are rarely spelled out.

They include:

  • board otherwise empty;
  • escape from the local position is good enough for life;
  • no effects from corners of the board not represented in the diagram;
  • seki is obviously a solution to a life problem.

On the other hand it is assumed that

  • ko is a solution;
  • there are worthwhile non-local ko threats.

There is usually no call to read ladders, but logically speaking we should assume all ladders are good. Note that being chased in a ladder doesn't count as escape.

To be quite precise is a little tricky. Something like this: we assume an otherwise empty board that is semi-infinite in any direction with an unmarked corner, but is a large band (to make ladders work); and we add in a second board as direct summand for ko threats to inhabit.

As far as the solution goes: in Japanese books it is considered enough to establish the status. That means life, death or ko. Matters to do with endgame plays and leaving ko threats, for example, aren't covered. I think that a solution would be preferred if it gave first capture in a ko to the attacker for a 'to kill' problem (resp. to the defender in a 'to live' problem) (see try to get first capture in a ko). Probably matters such as number of ko threats go beyond the normal specification of tsumego, however important they might be in a real game.

Here on this site you can find discussion of those extra matters in some particular cases.

On the J-groups page you can find some more talk about conventions: for example the explicit placement of stones as barriers to escape.

Charles Matthews


Note that "escape from the local position is good enough for life" also applies to stones surrounding the target groups.

[Diagram]

Seki

For example, in this diagram, we say that the marked stones are in seki. Of course, that is conditional on the outside stones being alive, so that makes the status of the target groups slightly uncertain. However, since all the outside groups can escape and it is not realistic to assume that any of these groups can be captured at this point of time, by convention, we take the marked stones to be in seki. Unconvinced readers can argue till the cows come home about what happens if Black starts attacking the exterior White group, or vice versa, but such arguments are not productive when all the diagram creator wants to do is to construct an example to convey some concept.

Such a convention spares the person making the diagram from having to give two eyes to every exterior group, and actually makes positions more realistic, like those appearing in actual games.

[Diagram]

Not yet seki

Of course, the convention mentioned above does not apply if it can be shown that some surrounding key stones can be captured. In this diagram, Black can capture the three key White stones at a, so we cannot claim that the marked stones are in seki if Black plays first.



--unkx80


See also:


This is a copy of the living page "Conventions in Life and Death" at Sensei's Library.
(OC) 2009 the Authors, published under the OpenContent License V1.0.
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