Reference:
Covering and piercing disks with two centers (Hee-Kap Ahn, Sang-Sub Kim, Christian Knauer, Lena Schlipf, Chan-Su Shin, Antoine Vigneron), In Comput. Geom., volume 46, 2013.
Bibtex Entry:
@article{journals/comgeo/AhnKKSSV13,
author = {Hee-Kap Ahn and
Sang-Sub Kim and
Christian Knauer and
Lena Schlipf and
Chan-Su Shin and
Antoine Vigneron},
title = {Covering and piercing disks with two centers},
journal = {Comput. Geom.},
volume = {46},
number = {3},
year = {2013},
pages = {253-262},
doi = {10.1016/j.comgeo.2012.09.002}
}