@article{01279105,
title = {Point shift differentials and extremal quasiconformal mappings.},
journal = {Annales Academiae Scientiarum Fennicae. Mathematica},
volume = {23},
year = {1998},
pages = {475-494},
zbl = {0927.30014},
language = {en},
url = {http://dml.mathdoc.fr/item/01279105}
}
Strebel, Kurt. Point shift differentials and extremal quasiconformal mappings.. Annales Academiae Scientiarum Fennicae. Mathematica, Tome 23 (1998) pp. 475-494. http://gdmltest.u-ga.fr/item/01279105/