Ko preparation

Before the ko in the top left  

/ is an exchange that White normally plays with the aim of fighting a ko. If Black wants to back down, he will not answer at . In this game, White does something before the ko. See 4-4 point low approach one-space high pincer for this joseki.

Ko preparation  

The exchange / is ko preparation. It may also look like a waste of a ko threat.

To understand this: it does 'waste' a threat, but the second threat for White in this area is bigger. This can be called promoting a ko threat.

The ko fight proper  

and so on set up the ko. White interpolates a second piece of preparation with / (the third threat here is bigger than the second).

The ko fight resolved  

When it comes, the ko fight is short. NB is not concerned with the ponnuki.

Variation: no preparation  

White has better shape than in this hypothetical result.

Since Black was presumably going to finish the ko immediately, White only needed one threat.

Black to win  

Variation: