Geertrui Van de Voorde. On sets without tangents and exterior sets of a conic. Discrete Mathematics, 311(20):2253-2258, 2011. [doi]
@article{Voorde11,
title = {On sets without tangents and exterior sets of a conic},
author = {Geertrui Van de Voorde},
year = {2011},
doi = {10.1016/j.disc.2011.07.010},
url = {http://dx.doi.org/10.1016/j.disc.2011.07.010},
researchr = {https://researchr.org/publication/Voorde11},
cites = {0},
citedby = {0},
journal = {Discrete Mathematics},
volume = {311},
number = {20},
pages = {2253-2258},
}