### Evaluating discriminant of a polynomial in Z_n[x]/<x^r-1>

Consider the following code

```
Zn=Zmod(n)
R = PolynomialRing(Zn,'x')
F = R.quotient((x**r)-1)
y=F((x+1))
f=F(y**n)
```

Clearly **f** will be a polynomial in xbar , I want to consider this polynomial as a polynomial in $ \mathbb{Z}[x] $ and evaluate its discriminant.

I tried ~~"f.polynomial()" ~~**"f.polynomial()"** but it is not working. Any suggestions ?