@article{GDZPPN002082985,
title = {The Problem of the Circular Billiard.},
journal = {Elemente der Mathematik},
volume = {47},
year = {1992},
pages = {108-113},
zbl = {0800.70051},
url = {http://dml.mathdoc.fr/item/GDZPPN002082985}
}
Waldvogel, Jörg. The Problem of the Circular Billiard.. Elemente der Mathematik, Tome 47 (1992) pp. 108-113. http://gdmltest.u-ga.fr/item/GDZPPN002082985/