Group safety level

Group safety level (GSL here) is one way of referring to the status of a group. Instead of just three terms (alive/unsettled/dead) in the middlegame it may be better to use richer, more nuanced language. For instance, we could use four levels: safe, fair, endangered, and dead.

Analysis of the GSL and how it can change depending on subsequent moves is a good way working out one's strategy. For instance if a move can change the safety level(s) of one or more groups, namely, can make one's own group(s) safer (higher in safety level) and/or the opponent's group(s) more endangered (lower in safety level), it can generate huge value through attacking or capturing stones, and preventing one's own stones being attacked or captured.

Notes

This page was created in response to a suggestion by dino1019 at https://senseis.xmp.net/?topic=13538.

Discussion

bugcat: How does GSL map to eye count? Let's say for the sake of simplicity that our granularity in eyes is 0 (no eyes), 0.5 (a gote eye), 1 (a sente eye or two gote ones), 1.5 (a sente eye and a gote eye) and 2 (two sente eyes). 0 is obviously dead and 2 is safe, but how about using three intermediate levels instead?

PJT 2023-02-18: This sounds rather like fractional eyes, though there are other values not covered above (¾, 1¼ and even, with ko, ⅓).

Malcolm 2023-02-20: I think these are different notions, even though they're related. Generally we tend to count eyes when groups are more or less completely surrounded; when their (potential) eyespace is more or less completely defined. The sort of situations one looks at in tsumegos. Whereas looking at the GSL can not only be useful for looking at such groups, but also for looking at groups where the eyespace is not yet fixed; where the shape has not yet been fixed. So GSL is useful for situations where the analysis is more about fighting/middle game/chuban instead of local tsumegos.

For instance, an outwards-facing wall often doesn't yet have clearly defined eyespace, so it's next to impossible to count its eyes. However its GSL is easier to evaluate; and the evaluation of GSLs and how they're affected by potential follow-up moves will often be helpful.

dino1019 2023-02-21: Malcolm is almost there. I can only expose that it's a 2-dimentional matrix with one as "has complete/incomplte/no base/eyespace/eyeshape" and the other as "with 0/1/2 way(s) out", and you guys have to figure out the rest; of course, different teachers or authors might come up with different matrices, as long as it makes sense. As a bonus, my teacher also deducts from this model that: "two fair groups of the same color and next to each other are subject to "double attack" and one or both become endangered"; but it takes time to digest.

xela: I think we need some examples to make this clear. Here is something I just made up. But if you have a better example, please delete mine!

 

Both of the marked groups are unsettled with no eyes. But white has plenty of options for defending, running away or sacrificing. The black group is heavy and in danger of being captured outright. Even though they both have the same status and same number of eyes, white is still safer than black. Is this what you mean by "group safety level"?

dino1019 2023-02-22: The group on the left is endangered, it has no eyeshape and has only one way out (note: how many ways out should be answered by reading and see if the group can escape to a bigger area of the board where it is not enclosed by enemy stones, the difficult scenarios are those related to "managing isolated weak group" (治孤)). The group on the right has no eyeshape and has about one (seemingly less than two) way out, so it's between endangered to fair, if I am not mistaken. I have to clarify the "sacrifice" part, it should be a different concept I name it 'sacrificability", but actually we do have related go terms: "heaviness/lightness" (重/輕) to indicate it; in a way, it is the "value" of the group. When a gruop is endangered, it can be sacrificed if it is light, it cannot if it is heavy; the heaviness or lightness depend on, upon being captured, (1) number of stones (the bone or skeleton) (2) number of empty spaces (the meat) (3) the group safety level increase, if any, of the capturing group and the increas of influence thereof. (Is this the "unbearable heaviness of go"?)