@article{10_4153_CJM_1972_100_7,
     author = {Beer, Gerald},
     title = {The {Continuity} of the {Visibility} {Function} on a {Starshaped} {Set}},
     journal = {Canadian journal of mathematics},
     pages = {989--992},
     year = {1972},
     volume = {24},
     number = {5},
     doi = {10.4153/CJM-1972-100-7},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1972-100-7/}
}