@article{RM_1977_32_3_a0,
     author = {Yu. D. Burago and V. A. Zalgaller},
     title = {Convex sets in {Riemannian} spaces of non-negative curvature},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {1--57},
     publisher = {mathdoc},
     volume = {32},
     number = {3},
     year = {1977},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RM_1977_32_3_a0/}
}