@article{ZNSL_1976_66_a1,
     author = {Yu. D. Burago},
     title = {Three-dimensional open {Riemannian} space of nonnegative curvature},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {103--113},
     publisher = {mathdoc},
     volume = {66},
     year = {1976},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1976_66_a1/}
}