This is answered by
. Black cannot prevent the marked white
stones from connecting out due to a shortage of liberties.
Connecting at prevents the shortage of liberties. But after
-
, black is again caught by a shortage of liberties.
The other way to prevent the connection under is to play immediately. Now,
is the tesuji white is looking for. After
, black cannot play a due to shortage of liberties.
and
are miai, if black plays
at
, white connects with
at
, and black still ends up with a false eye.