The comb formation is alive

Comb formation  

The comb formation is always alive. The points a and b are miai.

Comb formation  

The placement at is useless. Black answers at , and subsequently 3 and 4 are miai.

Comb formation  

When White attacks the group at , Black plays at . Now, 3 and 4 are miai.

Comb formation  

White here threatens a snapback at a. There is nothing to worry though, as does the trick.

--unkx80

Losing Liberties  

A key feature of this shape is that white may block both sides of the group in sente. For example, in this diagram forces Black to defend at or a. In addition....

Losing Liberties  

is threatening White a, Black b and , which is double atari. Black should defend at or a. (Black c completes 'the comb' nicely, but is a small mistake because it gives an additional ko threat to White)

These first-line blocks by White should not be played immediately, but are good ko threats - the chance to play them is unlikely to disappear, since black pushing out will be gote.