Two-space extension
is a two-space extension along the third line, a big fuseki point which creates a base for the group and prevents Black from attacking around the same point. This is one of the most common formations in go. The two-space extension on the third line cannot be cut without the help of surrounding stones, but can be attacked in various ways; see two-space extension - unobvious answers and L'ame du go.
The Black formation on the left is also a two-space extension, but on the fourth line. The White formation is not a two-space extension, but rather a large knight's extension. Both are useful for developing groups and/or creating a base, but less stable than the two-space extension on the third line.
In the fuseki, having an option for a two space extension is an important consideration when deciding how to play inside an opponent's framework or side position.
One major consideration is whether a two-space extension has nerai, or potential for sharp follow-up moves:
http://lifein19x19.com/forum/viewtopic.php?f=15&t=9491.
See also:
![[Diagram]](../../diagrams/37/500671409ec00dbba2fd143a970fe5e8.png)
![[Diagram]](../../diagrams/45/ab6fc15fb2612d236e23b61135ed4c18.png)
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