quotient of algebraic integer rings

This is my first time using sage so this might be a stupid question: I want to construct the field $K=\mathbb{Q}(\sqrt{2}, \frac{-1+\sqrt{3}i}{2})=\mathbb{Q}(\alpha)$, where $\alpha$ is a primitive element. Denoting its ring of algebraic integers $\mathcal{O}_K$, I want to compute the quotient ring $\mathcal{O}_K/\mathbb{Z}[\alpha]$. My code is like: K. = QQ.extension(x^2-2) L. = K.extension(x^2+x+1) a = L.primitive_element() O = L.ring_of_integers() za = ZZ[a] print O.quotient(za) But I always get an error: TypeError: unable to convert Relative Order in Number Field in w0 with defining polynomial x^2 + (2*d + 1)*x + d + 3 over its base field to Number Field in w with defining polynomial x^2 + x + 1 over its base field Any help is appreciated. Thanks.