polylist takes a list of arguments, tries to convert each into
a polynomial (see polynomial), and sets the class of the
list to "polylist".
as.polylist tries to coerce its arguments to a polylist, and
will do so for arguments which are polynomials or lists thereof.
is.polylist tests whether its argument is a polylist.
This class has several useful methods, such as taking derivatives
(deriv) and antiderivatives (integral),
printing and plotting, subscripting, computing sums and products of
the elements, and methods for c, rep, and
unique.