@article{turan1941external,
  title={On an external problem in graph theory},
  author={Tur{\'a}n, Paul},
  journal={Mat. Fiz. Lapok},
  volume={48},
  pages={436--452},
  year={1941}
}

@Inbook{Aigner2018,
author="Aigner, Martin
and Ziegler, G{\"u}nter M.",
title="Tur{\'a}n's graph theorem",
bookTitle="Proofs from THE BOOK",
year="2018",
publisher="Springer Berlin Heidelberg",
address="Berlin, Heidelberg",
pages="285--289",
abstract="One of the fundamental results in graph theory is the theorem of Turan from 1941, which initiated extremal graph theory. Turan's theorem was rediscovered many times with various different proofs. We will discuss five of them and let the reader decide which one belongs in The Book.",
isbn="978-3-662-57265-8",
doi="10.1007/978-3-662-57265-8_41",
}