The K-property of N billiard balls II. Computation of neutral linear spaces. Nándor Simányi — 1992 Inventiones mathematicae
Towards a proof of recurrence for the Lorentz process Nandor Simanyi — 1989 Banach Center Publications
Hard ball systems are completely hyperbolic. Simányi, Nándor; Szász, Domokos — 1999 Annals of Mathematics. Second Series