Peep

A peep (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 peep.

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

In all following examples red play horizontally and blue play vertically.

Example

In this position blue player can play 2 correct peeps - 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 peeps. Against a4, a5 red has a choice of playing b5 which improves their position. Similarly, against f2, f3 red should play d2.

Crucial peep

There is a great use for playing peeps. 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.