Turns out, the killing shapes are not just for killing, also good at producing seki situations.
seki is the mexican standoff (you know, like in Hong Kong movies... Mexican) of go.
What I mean is first-person-to-move dies, so no one moves, no one dies. A mexican standoff is more like mutually assured destruction. But, if you factor in this study then maybe I make sense.
Well, if they were cowboys at twenty yards and not Chinese at point blank doing something allegedly Mexican.
But I digress.
When a surrounded group has only one eye space, and it is almost filled (only one liberty remaining) with a killing shape, that group is dead. This is because when the group is completely surrounded, it is forced to take the killing shape by filling the last liberty. At that point, a nakade is played on the vital point, and the group will never enjoy a 3D Pixar film again (for at least one reason).
Killing Shapes and Seki
Turns out, a lot of times having a killing shape with two unfilled liberties surrounding it is enough to, if not kill the surrounding stones, at least make a seki.
To be more precise, if the intruding shape can me made to almost fill the eye space and still be a killing shape, it's dead. If the intruding shape is already a killing shape, does not almost fill the eye space (2 or more liberties remaining), but cannot almost fill the eye-space and retain a killing shape, then it's seki.
Black cannot directly capture the shape without entering into a killing-shape-almost-filled-eye-space scenario.
White can kill by playing a at any time (to create a killing-shape-almost-filled-eye-space). Black is dead.
Black cannot directly capture the white stones, because it forms a killing shape.
BUT, even when black's outer liberties are taken, white cannot capture black (ko threats aside) because extending to either a or b forms a non-killing shape. Black could directly capture and white could not prevent his forming two eyes.