A: 

By fixing the error.

Alex Reitbort
Knowing what abstract base type derivative needs to be created is a lot easier when you know the type.
Tarks
+1  A: 

Edit, IntelliSense, Quick Info (on my machine, Ctrl+K, Ctrl+I). For parameters, it's Parameter Info (Ctrl+K, Ctrl+P).

MichaelGG