is not as common as the invasion at a (see low invasion of mixed three space extension), because Black's response at a will usually connect the two black stones together. Alternatively, Black may choose to attack
with b.
alone is usually not a good play: usually
is used in conjunction with a white stone at c.
Trying to cut with is unreasonable. In this diagram, White has achieved nothing. If
is played at
, Black will cut at
.
Trying to live this way is too low for white, and tends to give away too much influence to Black. Later, Black a will capture .
Normally the wedge at is too big a sacrifice because it gives Black a ponnuki, but in some specific situations separating
may be worth the sacrifice. In some other situations
may be played at a, but Black b can seal the white group in.
With the stone
can be a more severe invasion than
. When
tries to connect,
and
works in co-ordination with
. Then
is placed in an excellent position, at the vital cutting point.
Charles In examples from actual pro games, the previous diagram occurs; but other variations do, too. For example here before rescuing the cutting stone
.
Also, Black may simply play tenuki after the invasion, treating the whole area lightly.