Belyi Function Decompositions for The Icosahedron of Genus 4

Abstract

The icosahedron $I_4$ of genus 4 is a dessin d'enfant embedded in Bring's curve $\mathcal{B}$. The dessin $I_4$ is related in some sense to a regular icosahedron $I_0$ embedded in the complex Riemann sphere. In particular, decompositions of Belyi functions $β_{I_0}: \mathbb{CP}^1 \rightarrow \mathbb{CP}^1$ and $β_{I_4}: \mathcal{B} \rightarrow \mathbb{CP}^1$ for $I_0$ and $I_4$ have the same lattice. The diagram of $β_{I_0}$ decompositions is already known. In the present paper we find $β_{I_4}$ decompositions. Note that $β_{I_0}$ decomposes into rational functions on $\mathbb{C}P^1$, while in case of $β_{I_4}$ we deal with maps between different algebraic curves.