The errors on line 6 and 7 here confuse me.
```function fail11616.D.a does not override any function```, seems to be wrong, since it does attempt to override a function. Isn't the first error sufficient?
```function fail11616.D.b cannot override final function fail11616.C.b```, I don't think this is quite a correct account of the error, since override is not stated anywhere.