  A singularity is said to be exceptional (in the sense of V. Shokurov), if for
any log canonical boundary, there is at most one exceptional divisor of
discrepancy -1. In our previous paper (math.AG/9805004) we found two examples
of exceptional canonical singularities: these are quotients by Klein's simple
group of order 168 or by its central extension of order 504. Now we classify
all the three-dimensional exceptional quotient singularities.

Algebraic Geometry