The following principles may be kept in mind when killing a group with a placement.
See: counting liberties
This is a standard life and death shape Carpenter's Square that if played correctly leads to a ko fight and for black; correct play begins with a placement, . The more liberties the harder it is to be killed. The aim is to live as long as possible. This principle not relevant when the placement is a sacrifice (see Principle 5).
See: eye in the belly.
Obviously if you can make 2 eyes do so. But in a situation where the placement cannot live by itself inside the territory of the opponent's group, having an eye may decide the outcome of the situation. Using the previous example, suppose the opponent unwisely plays elsewhere:
threatens to create an eye at square (and in fact kills white unconditionally).
Using the same reasoning,
The correct is to play underneath . This move seems unusual (placement within a placement) until one realise that
- removes the possibility of black making an eye
- Reduces liberty of
- is gote connected to the white group.
See: killing shapes.
Black is a bent four in the corner dead shape. If he plays at square in the next move he makes a bulky five which is dead standing. However if he plays at circle his shape is alive; white can capture it and live.
This simplistic diagram illustrates how, instead of looking for live shape, one wants the opposite (aka dead shape) with regard to a placement group that cannot live on its own. e.g. straight three, bent four in the corner, bulky five... etc., so that the opponent is forced to capture, and ends up with a territory that is a dead shape. This does not necessarily mean death for the opponent's group, but it at least forces further play (e.g. escape into the centre, link up with another group, kill an outside group) to live.
A group of stones is vulnerable to oiotoshi if it ends up with 2 liberties. No matter how brilliant a move is, it can only reduce the liberties of an attacked group one by one. A placement that leads to oiotoshi therefore requires a targeted group with 3 liberties (or you can reduce the liberties to 3 by other means).
The correct move begins with , which makes no sense until one sees it as a way to force the white stones to end up with 3 liberties.
None of the black stones can live in its own. Their sole purpose is to reduce the liberties of the white groups to 3 (circles), so that black's play at