@article{GDZPPN002067927,
title = {Homomorphisms of constant stretch between M\"obius groups.},
journal = {Commentarii mathematici Helvetici},
volume = {66},
year = {1991},
pages = {155-168},
zbl = {0719.30035},
url = {http://dml.mathdoc.fr/item/GDZPPN002067927}
}
Tukia, Pekka. Homomorphisms of constant stretch between Möbius groups.. Commentarii mathematici Helvetici, Tome 66 (1991) pp. 155-168. http://gdmltest.u-ga.fr/item/GDZPPN002067927/