I am looking for a reference on dihedral, tetrahedral, or octahedral forms. As far as I read, they are some cuspidal automorphic forms on $GL(2)$ induced from $GL(1)$. Dihedral is from $GL(1)/K$ to $GL(2)/\mathbb{Q}$, where $K$ is a quadratic extension of $\mathbb{Q}$. But is this the same for tetrahedral or octahedral forms? What's their constructions?

## 1 Answer

$\begingroup$
$\endgroup$

I think a basic reference is Serre's paper "Modular forms of weight one and Galois representations” in Algebraic Number Fields, ed. by A. Frohlich, ̈Academic Press, 1977, 193–268; also in OEuvres, Vol. III, Springer- Verlag, Berlin, 1986, 292–367.