About our contracts and aspect discussion:

I think it is useful to try to generalize

@TECHREPORT{liskov-wing-bs,
AUTHOR = "Barbara Liskov and Jeannette M. Wing",
TITLE = "Behavioral Subtyping Using Invariants and Constraints",
INSTITUTION = "CMU",
YEAR = 1999,
MONTH = July,
NUMBER = "CMU-CS-99-156"
}

to aspects. The idea of an aspect is to provide
a refinement to existing behavior. The earlier work
of Pierre America is also relevant 

@INPROCEEDINGS{america:pool-I,
AUTHOR = "Pierre America",
TITLE = "A Parallel Object-Oriented Language with Inheritance and Subtyping",
BOOKTITLE = oopsla,
YEAR = "1990",
ADDRESS = "Ottawa, Canada",
PAGES = "161-168",
EDITOR = "N. Meyrowitz",
PUBLISHER = "ACM Press",
NOTE = "joint conference with ECOOP"
}

-- Karl