Notes:

The second special case is really an exception to the first case, which is that when the class is subclassed directly from Object, the superclass of the class's singleton class is the class named Class.

This is why the superclass of the singleton class of Numeric is the class named Class.

Note that the superclass of the singleton class of Numeric is not the singleton class of Class, it is Class itself.

This is why if you add an instance method to the class named Class, it is available as a class method on all classes.