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).
Blacks best defence after is to save his stones with , forcing . Later Black can play at a as a big ko threat: White needs to answer at b or his group dies.
W at 4 would remove the ko threat and capture the stones. That would be bigger than .
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.