  Large-scale computer simulations involving more than a million particles have
been performed to study the melting transition in a two-dimensional hard disk
fluid. The van der Waals loop previously observed in the pressure-density
relationship of smaller simulations is shown to be an artifact of finite-size
effects. Together with a detailed scaling analysis of the bond orientation
order, the new results provide compelling evidence for the
Halperin-Nelson-Young picture. Scaling analysis of the translational order also
yields a lower bound for the melting density that is much higher than
previously thought.
