BibTeX: 
@article{Combinatorics_Words_Graph_LemmaAFP,
author = {Štěpán Holub and Štěpán Starosta},
title = {Graph Lemma},
journal = {Archive of Formal Proofs},
month = may,
year = 2021,
note = {\url{https://isaafp.org/entries/Combinatorics_Words_Graph_Lemma.html},
Formal proof development},
ISSN = {2150914x},
}
