@article{10_4153_CJM_1987_039_7,
     author = {Erdahl, R. M. and Ryshkov, S. S.},
     title = {The {Empty} {Sphere}},
     journal = {Canadian journal of mathematics},
     pages = {794--824},
     year = {1987},
     volume = {39},
     number = {4},
     doi = {10.4153/CJM-1987-039-7},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1987-039-7/}
}