An unsettled shape is a shape whose life and death depends on whoever gets to play first (see sente).
If Black plays at a, he'll live; if White plays there she'll kill Black.
This is another simple shape which is unsettled.
If White plays first, she plays , and her group is alive in a straight four since a and b are miai.
If Black plays first, then White is killed by and
.
See also: