@article{701450,
     title = {Spingroups and spherical means III},
     booktitle = {Proceedings of the Winter School "Geometry and Physics"},
     series = {GDML\_Books},
     publisher = {Circolo Matematico di Palermo},
     address = {Palermo},
     year = {1989},
     pages = {[295]-323},
     mrnumber = {MR1009582},
     zbl = {0709.35077},
     url = {http://dml.mathdoc.fr/item/701450}
}

Sommen, F. Spingroups and spherical means III, dans Proceedings of the Winter School "Geometry and Physics", GDML_Books,  (1989), pp. [295]-323. http://gdmltest.u-ga.fr/item/701450/