Under The Stones Sacrifice Shape List
Sacrifice shapes which lead to the under the stones tesuji.
Look out for these!
Anonymous: A more common name is Squared Four.
If the three stones are captured, the one lonely stone can cause a shortage of liberties, which allows under the stones. Example: http://www.goproblems.com/prob.php3?id=438
Also, a captured empty triangle can cause an under-the-stones-ish capture, but for it to work, black must remove an outside liberty after white captures. This can, however, lead to interesting connection tesujis:
Black can connect even if white captures the 3 stones.
DrStraw: Better for B to play back into the center of the 3 stones than to fill an outside liberty. The effect on B'S shape is the same, but W is not as good.
unkx80: No, the sacrifice shape in the problem is actually bulky five, a generalization of squared four.
Kuolema: How does this lead to Under The Stones tesuji? Show me an example.
("another bent three" diagram moved to "in the corner" section. -bass)
unkx80: Making a more general statement, I believe the sacrifice stones may be the following shapes, with the optional addition of stones in the x direction or beyond.
Bill: The only (non-nakade) example I know of is in the corner, where it is not a question of an eye, but of points.
Black picks up 0.5 point.
OC, if we are going to include shapes where the question is points, there is no end. E. g., bent seventeen.
This is a 2/3 point Black sente (unless White is komaster, when it is worth 1 2/3 points).
Charles The one time it actually happened to me ...
... was when I made the mistake of playing here, thinking it was a snapback .
Bill: I think this is an example of the stupid four (). It's the sacrificial shape, not the capturing shape, that is in question.
OC, since a nakade can be under the stones, any nakade shape might qualify. <shrug> But we don't usually think of making that shape as tesuji.