# View polynomial over a field extension as a polynomial in the basis elements of the extension

I have a finite field extension L/K, with basis 1, z, ..., z^n, and a polynomial f in L[x,y]. I would like to regard f as a polynomial in z and obtain its K[x,y] coefficients as such. How can I do this?

Can you give us some concrete example ?

Maybe have a look at the documentation ?