Reading Width

Experienced level  

An experienced player doesn't need to explore this situation, because he knows White can kill at a.

Vital point knowledge  

Someone who doesn't know this position by heart, but has some basic knowledge about vital points, will normally investigate only a and b.

Vital point knowledge  

After the - exchange, one will take another look at a and b, before reaching conclusion.

Vital point knowledge  

Likewise here.

So, for a player with basic knowledge of vital points, the width of this position is 2 at each choice point.

Complete beginner  

For a complete beginner, not having any knowledge of vital points or eyes, any of the six points is a viable starting point. This gives a width of 6 at move 1, 5 at move 2, and so on. Potentially there are 720 branches in the search tree up to depth 6. However, some will be illegal, and some will not be reached in a search because the black stones will already have been captured. Furthermore, if the beginner tries depth first search, as humans usually do, and remembers already visited positions, he will stop at a position that he has reached before, by permutation of moves. So in practice the beginner will not take all of the branches of the search tree. Still, this position is out of reach for a complete beginner, unless gifted with exceptional search abilities.