It is important to atari the stone in the correct direction.
If here, then after
, the
stone is captured.
Under the stones - wishful thinking
Players who know the under the stones technique may be tempted to think of this more convoluted solution. (Note the tesuji of that forces Black to make an additional approach move.) Alas, this line is wishful thinking - see Under The Stones Problem 6 for the reason why it doesn't quite work.
Eaglehelm: Why does the above diagram not work?
unkx80: See the solution to Under The Stones Problem 6 for the details. In summary, in this problem Black can kill White unconditionally, but by applying the under the stones technique, Black can kill only by winning a ko.