[0815test]

Implementation inheritance may have its uses, but it's not for the faint of heart. Its defining feature is _open recursion_; that is, defining an object's external interface (its bundle of public and protected methods) in terms of itself (in that any method may be defined as calling any other method of the same external interface) and then leaving the whole thing open for arbitrary overriding in "derived" classes, via a "tying the knot" trick. Most treatments of OOP brush over this feature, but it creates a huge amount of complexity. It is even proper to say that something like this should be avoided at all costs, IMHO.