----- LAW OF DEMETER (Smalltalk-80, object version) ----
In all message expressions inside a method M 
the receiver must be one of the following objects:
  - an argument object of M including objects in 
      pseudo variables self and super or
  - an instance variable object of the class to which M
      is attached.
(Objects created by the method and objects in global 
variables are viewed as being passed by arguments.)
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