\begin{abstract}
We introduce a simple, programming 
language independent rule (known in-house as the Law of \demsign) which
encodes the ideas of encapsulation and modularity in an easy to follow form
for the \oo \/ programmer.
% WHAT IS IN THE PAPER FOR THE USER ?
You tend to get the following interrelated benefits when you 
follow the Law of Demeter: 
Easier software maintenance, 
less coupling between your methods,
better information hiding,
narrower interfaces,
methods which are easier to reuse,
and easier correctness proofs using structural induction.
%We show relationships between the Law and software
%engineering techniques, such as coupling control, information hiding,
%information restriction, localization of information, narrow interfaces
%and structural induction. 
We discuss two important interpretations of the
Law (strong and weak) and we prove that any \oo \/ program can be transformed
to satisfy the Law.
We express the Law in several languages which support object-oriented
programming, including Flavors, Smalltalk-80, CLOS, C++ and Eiffel.
\end{abstract}