If you are using modules as OO classes then you don't need to import them again if they are already inherited.

(Theoretically you might to import functions from these base classes too, but mangling OO and exporting is bad practice.)

Update

After reading choroba's answer... What do you exactly mean with:

> This needs a functionality of module B.

If you mean inherited methods in B1 objects , then the answer is no !

If you mean objects constructed from B - i.e something like B->new() - then the answer is of course yes !

( for the reasons choroba listed.)

If you mean something else please be more explicit.