@article{10_2307_121019,
     author = {N\'andor Sim\'anyi and Domokos Sz\'asz},
     title = {Hard ball systems are completely hyperbolic},
     journal = {Annals of mathematics},
     year = {1999},
     volume = {149},
     number = {1},
     doi = {10.2307/121019},
     zbl = {0918.58040},
     url = {http://geodesic.mathdoc.fr/articles/10.2307/121019/}
}