Block on the wider side

The 3-3 point invasion  

This Go proverb is meant for the situation in this diagram: White has just invaded at the 3-3 point below Black's 4-4 point (see 3-3 Point Invasion). On which side should Black block, at a or at b? The general rule is to block where your extension is wider or the potential moyo is larger.

An example  

In this diagram is further away than (so it is the wider extension), so Black blocks at rather than a.

A second example  

Here and are at the same distance, but if one looks beyond it, the upper moyo still extends further than the left one, so again is the correct move.

Black to play  

tderz: Blocking from the wider side means that you yourself will get more potential for territory, while the opponent will get less space, even lacking stability.

Black to play: a or b? ^[10]

Block from the wider side  

Correct: Black gets a wide extension from his -shimari and induces the natural corner moves +.

The white position is cramped, imagine a (later) black move a!

Blocking from the smaller side  

Incorrect: the -shimari is devalued, the extension is less cramped than in the correct diagram and
if Black closes the corner now with a, there are still later "imponderabilities" as b etc.