Simanyi N., Szasz D. The Boltzmann-Sinai Ergodic Hypothesis for Hard Ball Systems (383K, POSTSCRIPT) ABSTRACT. We consider the system of $N$ ($\ge 2$) elastically colliding hard balls with masses $m_1,\dots,m_N$ moving uniformly in the flat unit torus $\Bbb T^{\nu}$, $\nu\ge 3$. It is proved here that the arising billiard flow possesses the K-mixing property for almost every distribution of the masses $m_1,\dots,m_N$.