There is a type of programming task which is made much easier by the fact
that each instance of a subclass is also an instance of
the generic class. In our case, each instance of a geometry subclass is
also an instance of the generic Geom class.
So if our program, like geomview, is designed to
deal with many different types of geometry objects, we can simplify
the program structure by always working with the Geom class rather
than the specific subclasses. GeomLoad and GeomDraw, for example,
work perfectly well to load and draw instances of any subclass, too.
Of course it takes some work to make sure this works, but that work
has already been done for you.