Weak rectangular six in the corner

Weak 6  

If in the Rectangular six in the corner the corner point is white, the shape is a bit weaker.

Black can live with 5 points of territory by playing at a.

What white can do depends on the number of outside liberties.

Kill  

In case the short side has no outside liberties, it's straightforward.

Kill  

When the long side has no outside liberties, then still kills.

Kill  

When both have an outside liberty, no longer works

Ko  

And it's a ko