Weakly--exceptional quotient singularities

A singularity is said to be weakly–exceptional if it has a unique purely log terminal blow up. In dimension $2$, V. Shokurov proved that weakly–exceptional quotient singularities are exactly those of types $D_n$, $E_6$, $E_7$, $E_8$. This paper classifies the weakly–exceptional quotient singularities in dimensions $3$ and $4$.