@article{GDZPPN002057255,
title = {The spherical derivative of meromorphic functions in the neighbourhood of an isolated singularity.},
journal = {Commentarii mathematici Helvetici},
volume = {33},
year = {1959},
pages = {196-205},
zbl = {0086.06402},
url = {http://dml.mathdoc.fr/item/GDZPPN002057255}
}
Lehto, Olli. The spherical derivative of meromorphic functions in the neighbourhood of an isolated singularity.. Commentarii mathematici Helvetici, Tome 33 (1959) pp. 196-205. http://gdmltest.u-ga.fr/item/GDZPPN002057255/