Interfaces/abstract classes in own libraries

[eluser]Unknown[/eluser]
Hello everyone,
in my Application I'm building 3 very similar libraries and I'd like to make them all implement one interface or at least extend from a common abstract class.

This seems not to be what the developers had in mind when creating CI, so I'd like to know if anyone ever did this and/or if there is a best practice on how to achieve that?

[eluser]Nick_MyShuitings[/eluser]
I think the only thing you'd have to do to achieve this, would be a require_once in the beginning of each of these libraries. Then extend whatever you wish to extend.