@article{MAN_1992__294_4_165021,
     author = {Ilkka Holopainen and Seppo Rickman},
     title = {Quasiregular mappings of the {Heisenberg} group.},
     journal = {Mathematische Annalen},
     pages = {625--644},
     publisher = {mathdoc},
     volume = {294},
     number = {4},
     year = {1992},
     zbl = {0754.30018},
     url = {http://geodesic.mathdoc.fr/item/MAN_1992__294_4_165021/}
}