Algebraic surfaces with canonical map of degree 13 15 17 18 21 22

Abstract

In this note, we construct some minimal smooth surfaces of general type with canonical map of degree $13,15,17,18,21,22$. These surfaces are constructed as ${\mathbb{Z}}_3^2$-covers of a blow-up of ${\mathbb{P}}^1\times {\mathbb{P}}^1$.

The statement of the degree of canonical maps is wrong