We have class Numeric, class Integer, class Fixnum, and class Bignum.
It seems that literal numbers are converted to objects of Fixnum/Bignum.
It also seems that Numeric/Integer are meant only for inheritance and
not instantiation, yet they aren't abstract classes.   Is there a write-up
on all this, the basic intention, the details?  I find the topic just
glossed over in the Pick-axe book.

Thanks.