Two-stone edge squeeze
The two-stone edge squeeze tesuji , also known as the "stone tower", is commonly used in capturing races and can occur not just in the corner, but also anywhere on the edge. Also known as stone monument tesuji, stone tower tesuji, stone pagoda squeeze, or tombstone squeeze.
See also two-stone corner squeeze.
and form the first part of the two-stone edge squeeze tesuji. Note that is forced, as atari from the other direction leads to the capture of one of the two groups cut apart.(see later) also prevents the atari at a.
The throw-in at , which is the second part of this tesuji, forces the capture at . is an atari on three Black stones; White lives if these three stones are captured (see capture three to make an eye).
The best plays locally for Black after are successive exchanges, saving the stones: for , for and a for b. As a matter of technique it is often better to not play these exchanges immediately as they can be useful if they are kept in reserve for some time, as ko threats. It's a question of timing. Generally a will not be played before the endgame, whereas and may well be played before the endgame.
Giving atari at the wrong side makes it all too easy for White. Not only Black can do nothing to prevent White capturing the stones, but also White can in the endgame capture the stones (by playing at a). But probably a tenuki elsewhere is bigger than this.
This particular position is also known as the two-stone corner squeeze.
is too slack. Up to , White wins the capturing race by one move.