ptayl is used to rewrite a polynomial P depending of x
in terms of the powers of (x-a)
(ptayl means polynomial Taylor)
ptayl takes two arguments: a polynomial P given by a symbolic expression or by the list of its coefficients and a number a.
ptayl returns the polynomial Q such that Q(x-a)=P(x)
Output, the polynomial Q:
i.e. for the example :