@article{CMH_1986__61_140069,
     author = {Richard Fehlmann},
     title = {On a fundamental variational lemma for extremal quasiconformal mappings.},
     journal = {Commentarii mathematici Helvetici},
     pages = {565--580},
     year = {1986},
     volume = {61},
     zbl = {0624.30029},
     url = {http://geodesic.mathdoc.fr/item/CMH_1986__61_140069/}
}