Alive
| Table of contents | Table of diagrams Standard example Two white groups are alive Black cuts, White makes a second eye Black makes the eye false, White connects |
Common notion
Being alive is one possible status of a group, as opposed to being dead; in-between groups are called unsettled, or in more open positions groups that are not clearly alive may be described as weak groups.
A group may also be alive with territory or merely in seki.
For example, the following black group in the corner is alive with two eyes which make points of territory.
![[Diagram]](diagrams/27/d1e9f4125c57b201381cfe5118c9fd8e.png)
For an introduction to the notion of being "alive". Informally, a group is often described as "alive" if it can make a living shape when attacked. [4] See Alive - Introductory.''
Strict notion
First approach
Alive is a property of a string or a group of strings if one of the following aspects applies:
- Currently the string is uncapturable, or capturable but belongs to an alive group.
- Currently not all of the group's strings can be captured in alternating play when the opponent plays first.[1]
- The rule set in use defines the term and it applies during scoring.
Classification of the life of strings
All types of life of strings are classified as follows:
- it belongs to an independent life group or
- it is one of the following:
- uncapturable;
- capturable-1 (a new permanent stone can appear under the string);
- capturable-2 (a new permanent stone can appear in a local environment bounded by uncapturable or capturable-1 stones).
It is ![[ext]](images/extlink.gif)
equivalent to characterise independent life by transformation to two-eye-formation or by the three types of capturability [7]. The latter cover all live groups, regardless whether independent life [8] or seki.
Special types of groups having life
There are several ways in which a group can 'live':
- it is independent life so has or can make two eyes;
- it lives in seki; [5]
- it is pass-alive, i.e. cannot be captured however often the defender passes;
- equivalently, it satisfies Benson's condition: every chain in it has two chain-eyes within it.
Special shapes of life
- it lives in disturbing life, such as double ko or double ko seki; [6]
- moonshine life, where it can only be captured via ko but the defender has indefinitely many unremovable ko threats; [2]
- it is a Two-headed dragon. [3]
Tactics for living
Tactics for making live groups can combine threats: to make an eye, or to connect.
![[Diagram]](diagrams/19/3bfa7efc1d74c1898e69b8292d51f63e.png)
In this example the right-hand white group is alive in the strict sense, with two completely explicit eyes. The following diagram shows that the left-hand white group is also alive in alternating play. The right hand group is of some help for that.
![[Diagram]](diagrams/4/2a79a20350195016b178e81088ab2933.png)
with 
for ![[Diagram]](diagrams/34/05dea3bed72ac8351805c9d05fb1996e.png)
Notes
[1] That is, the group as a whole isn't one that the opponent, with the move, can forcibly capture. Stones within it may be captured.
[2] It depends on the rules whether moonshine life is alive. It is dead under most modern versions of the rules. A certain rare kind of moonshine life is possible under AGA rules, however.
[3] Depending on the chosen definition of eye?, the two-headed dragon ("Dragon Eats its Own Tail") is merely a special case of two eyes.
[4] A group that does not obviously have two eyes, or is not clearly in seki, is still alive if it is guaranteed to be able to get two eyes or make seki, regardless of who plays first. By this extended definition, groups that seem to be alive, or are alive can die if a player is negligent. See pass-alive, also ambiguously called unconditional life.
[5] Depending on the rules, a seki can also contain some dead stones neither player wants to remove.
[6] Depending on the rules, the ko stones of a disturbing life are either alive or dead.
[7] For definitions of the types of capturability, see the Japanese 2003 Rules.
[8] Also called two-eye-alive group.
See also
- The Eyes Collection.
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