Square nine
Square nine is unconditionally alive.
If White plays in the middle of the eye at , Black can ignore three moves and still live. The shape is only interesting in the corner.
Bill: This strikes me as strange. This shape is alive. By the tsumego usage, it is unconditionally alive, meaning that, with correct play, White to play cannot even make a ko. In the Benson sense, it is not unconditionally alive, because it cannot live by always passing. Regardless of which meaning is intended,
makes no difference. It is unconditionally alive or not, regardless of whether Black makes that play. This needs a rewrite, IMO.
unkx80: You'd better ask Dieter what he's trying to express here.
However, Black should not allow White to create an eye in the belly. In this position, Black is dead.