@article{1183499927,
author = {Carath\'eodory, Constantin},
title = {The most general transformations of plane regions which transform circles into circles},
journal = {Bull. Amer. Math. Soc.},
volume = {43},
number = {12},
year = {1937},
pages = { 573-579},
language = {en},
url = {http://dml.mathdoc.fr/item/1183499927}
}
Carathéodory, Constantin. The most general transformations of plane regions which transform circles into circles. Bull. Amer. Math. Soc., Tome 43 (1937) no. 12, pp. 573-579. http://gdmltest.u-ga.fr/item/1183499927/