Voir la notice de l'article provenant de la source European Digital Mathematics Library
@article{PORMA_1952__11_3_114707, author = {Bourgin, D.G.}, title = {Sets of visibility}, journal = {Portugaliae mathematica}, pages = {137--140}, publisher = {mathdoc}, volume = {11}, number = {3}, year = {1952}, mrnumber = {0051503}, zbl = {0047.28901}, language = {en}, url = {http://geodesic.mathdoc.fr/item/PORMA_1952__11_3_114707/} }
Bourgin, D.G. Sets of visibility. Portugaliae mathematica, Tome 11 (1952) no. 3, pp. 137-140. http://geodesic.mathdoc.fr/item/PORMA_1952__11_3_114707/