X U A B --soft (disallowed)
--mixed X B B
--hard B B B
- --merge X B B
+ --merge B B B
working index HEAD target working index HEAD
----------------------------------------------------
X U A A --soft (disallowed)
--mixed X A A
--hard A A A
- --merge (disallowed)
+ --merge A A A
X means any state and U means an unmerged index.