@article{10_4064_aa139_3_2,
     author = {Jan Florek},
     title = {Billiards and the five distance theorem},
     journal = {Acta Arithmetica},
     pages = {229--239},
     publisher = {mathdoc},
     volume = {139},
     number = {3},
     year = {2009},
     doi = {10.4064/aa139-3-2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/aa139-3-2/}
}