Klaus, Nick at MIT made some good suggestions to dealing with adding
slots to instances. Here they are:

>        I may not understand what the problem is exactly, but for the
>instances, doesn' t it mean that when you want to dynamically add a slot
>to an instance, you have to add it to its class?
>        It even seems reasonable to me, for you probably want to add the
>slot to other instances of the same class. Otherwise, you might as well create
>a new subclass with a single instance (to start with) and inheriting
>every slot from its superclass, having as only slot of its own the new slot
>desired for the instance.
>        So, modifying the class automatically doesn't violate your principle
>and is consistent with what the user is asking for.

My response:
Your two solutions both sound reasonable.  Probably adding the slot to
the class when a slot is dynamically added to an instance would be the
most efficient thing, since I agree that you will probably end up adding
the same slot to other instances of the same class.

What do you think?

Also, could you give me an example of an instance having a relation
to another instance?
