At least is a beginning. On Linux all tests and the 
modified test_descr.py pass.

A few cases in test_descr.py are commented out, 
maybe they should be adjusted, reconstructed.

For order disagreement situations: backup logic 
picking an element from the first non-empty list and 
removing it from all lists, where it appears, and just 
throwing a warning instead of an exception could be 
put where I set the exception now.

Although in the long run people should learn to use 
consistent hiearchies anyway.

PS: I was wondering how to get/reuse lst.remove(o) 
functionality from C, apart through 
PyObject_CallMethod...