- 1
-  A number of notations exist for
describing relations, e.g. UML (Unified Modeling Language).
- 2
-  In most object-oriented languages, a dot notation is used.
However, the dot notation was already used for records and modules, so a
new symbol was needed.
- 3
-  The private of Objective CAML corresponds to
protected of Objective C, C++ and Java