Karol Pak. The Friendship Theorem. Formalized Mathematics, 20(3):235-237, 2012. [doi]
@article{Pak12a,
title = {The Friendship Theorem},
author = {Karol Pak},
year = {2012},
url = {http://www.degruyter.com/view/j/forma.2012.20.issue-3/v10037-012-0028-7/v10037-012-0028-7.xml},
researchr = {https://researchr.org/publication/Pak12a},
cites = {0},
citedby = {0},
journal = {Formalized Mathematics},
volume = {20},
number = {3},
pages = {235-237},
}