Empty triangle
This shape is an empty triangle, empty referring to the point at .
The empty triangle is bad, generally, being inefficient and prone to shortage of liberties. But there are also good empty triangles (see guzumi).
In contrast, the full triangle, with a White stone at , is good shape.
Additional Black stones, such as the legs of a, or b or c, give this shape different efficiency and shortage-of-liberties characteristics, and as such it is no longer called an empty triangle, although it may still be so-called stupid shape (gukei?).
The presence of the stones in place mean that this is not an empty triangle either, but rather a diamond or ponnuki with an extra stone at
, a common shape.
Empty triangle is also sometimes called the devil's shape (onigatachi), because it brings to mind the long nose of one kind of Japanese demon.