Nozoki

A nozoki (term borrowed from Go) is a forcing move to which opponent has just a single answer to defend against an immediate threat. This situation occurs if one threatens to cut a connection between major groups or key stones of opponent's. The stone causing this threat is called a nozoki.

Sometimes it's hard to tell if a move is forcing, i.e. if the nozoki is correct or wrong. Playing correct nozokis is one of the most sophisticated aspects of hex strategy.

In all following examples red edges are vertical ones and blue edges are horizontal ones.

Example


In this position blue player can play 2 correct nozokis - c4 or c3. In case of playing c3, red has to defend with c4. In case of playing c4, red has to defend with c3. Otherwise red loses the game.

Notice that moves on a4, a5, f2 and f3 are wrong nozokis. Against a4, a5 red has a choice of playing b5 which improves their position. Similarly, against f2, f3 red should play d2.

Crucial nozoki
There is a great use for playing nozokis. In certain conditions a player can benefit from them and claim victory. Look at the following example:



The only winning move for blue is the peep on d6. If blue misses it the game proceeds as follows and the winner is red.



If d6 is played then blue win.

