MathOverflow will be down for maintenance for approximately 3 hours, starting Monday evening (06/24/2013) at approximately 9:00 PM Eastern time (UTC-4).

2 I changed the set-up a bit. It was too general and I emphasized my motivation.; deleted 1 characters in body

Let $Y$ be a normal projective surface, let $X$ be a smooth projective surface and let $\pi:Y\longrightarrow X$ be a finite morphism. Why are all singularities of $Y$ cyclic quotient singularities? And what does this mean? Furthermore, why are these singularities rational? And again, what does that mean? (I edited the question. So the example of Ekedahl doesn't work anymore.)

Take a minimal resolution of singularities $\rho:Y^\prime\longrightarrow Y$. Then the above apparently shows that $R^0 \rho_\ast \mathcal{O}_{Y^\prime} = \mathcal{O}_Y$ and $R^i \rho_\ast \mathcal{O}_{Y^\prime} = 0$ for $i>0$. Is this something special for surfaces?

The reason I ask this question is the following.

If $Y$ is a normal variety (say over the field of complex numbers). Then does numbers) with the above terminology still make sense? More importantlydata, do we still have $R^0 \rho_\ast \mathcal{O}_{Y^\prime} = \mathcal{O}_Y$ and $R^i \rho_\ast \mathcal{O}_{Y^\prime} = 0$ for $i>0$.

Note. The case of a surface over the complex numbers is dealt with in Compact complex surfaces by Barth, Hulek, Peters and van de Ven. I believe they show that cyclic quotient singularities are rational in this case.

1

# On minimal resolution of singularities and the type of singularities

Let $Y$ be a normal surface. Why are all singularities of $Y$ cyclic quotient singularities? And what does this mean? Furthermore, why are these singularities rational? And again, what does that mean?

Take a minimal resolution of singularities $\rho:Y^\prime\longrightarrow Y$. Then the above apparently shows that $R^0 \rho_\ast \mathcal{O}_{Y^\prime} = \mathcal{O}_Y$ and $R^i \rho_\ast \mathcal{O}_{Y^\prime} = 0$ for $i>0$. Is this something special for surfaces?

If $Y$ is a normal variety (say over the field of complex numbers). Then does the above terminology still make sense? More importantly, do we still have $R^0 \rho_\ast \mathcal{O}_{Y^\prime} = \mathcal{O}_Y$ and $R^i \rho_\ast \mathcal{O}_{Y^\prime} = 0$ for $i>0$.

Note. The case of a surface over the complex numbers is dealt with in Compact complex surfaces by Barth, Hulek, Peters and van de Ven.