@article{JEMS_2010_12_4_a6,
     author = {Stefan Ivanov and Ivan Minchev and Dimiter Vassilev},
     title = {Extremals for the {Sobolev} inequality on the seven-dimensional quaternionic {Heisenberg} group and the quaternionic contact {Yamabe} problem},
     journal = {Journal of the European Mathematical Society},
     pages = {1041--1067},
     publisher = {mathdoc},
     volume = {12},
     number = {4},
     year = {2010},
     doi = {10.4171/jems/222},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/jems/222/}
}