I would just like to remind, that directories with union mounts do present "inheritance". Because inheritance is the most defining characteristic of the OO paradigm, is is quite fair to say that file systems in Plan 9 are (persistent, networked) "objects" in the classical OO sense.
You can take a standard /net and bind your own modified /net as an union with it, hiding some files, replacing some files, and leaving some files intact. That is, you can take a father object, inherit some of its functionality to the child object (the union) untouched, modify some functionality (perhaps filtering ctrl files and writing back to original ones), and remove some. Exactly like in SmallTalk or C++ or Java.
