3463 enclosure
Hikaru79: Can this enclosure be invaded in any way? Or does the 3-4 assure the fact that black has the corner?
Bob McGuigan: White can invade at a or b and live or escape but most of the many variations are unfavorable for white. Here are some for the move at a:
If is one space to the right, attaching on the 6-3 stone, White can live inside but gets sealed in and Black gets too much thickness on the outside. For example:
For the invasion to be a success White usually needs support on the outside.
unkx80: Just to add on, the "support on the outside" usually means the existence of a White stone at a or b, and that stone has to be a part of a strong group.