combos

corner  

White can cut Black, but it requires two good moves to do it. The first is easy to see:

 

White completes the separation process with the following blow, which looks vulgar but is actually unstoppable, because a and b are turned into miai after :

Double Wedge?  

Please note that Black's alternative reply fails like this:

 

Please note also that White cannot reverse the order of moves, as Black can survive in the following fashion, finishing off with a:

 

It is interesting to recall that chess players use the term "combination" to describe clever sequences of tactics. Learning to think of tactics in this more extended fashion can only do good for your reading skills in Go. When you cannot find a simple way to solve a tactical problem, try finding a way to set up a solution by playing nearby.

Here is another example:

 

Black can cut White in two, but the simple cut at x fails like this:

 

The answer is to use a combination in which the first move makes the cut possible later:

 

The result is unappealing for White if she tries to resist, as Black links up beneath her and sets her floating:

 

What happens if White resists more strongly with ?

 

Black captures the marked white stones with the sequence up to . --Hans

This can turn into a ko after White's throw-in at a. Try reading out at a, instead. --Charles

No, there is no ko. If white throws in at a, black does not capture the throw-in, but gives atari at b. --Andre Engels

Good point. --Charles