@article{SIGMA_2016_12_a35,
     author = {Sorin V. Sabau},
     title = {The {Co-Points} of {Rays} are {Cut} {Points} of {Upper} {Level} {Sets} for {Busemann} {Functions}},
     journal = {Symmetry, integrability and geometry: methods and applications},
     year = {2016},
     volume = {12},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SIGMA_2016_12_a35/}
}