BibTeX: 
@article{Projective_GeometryAFP,
author = {Anthony Bordg},
title = {Projective Geometry},
journal = {Archive of Formal Proofs},
month = jun,
year = 2018,
note = {\url{http://isaafp.org/entries/Projective_Geometry.html},
Formal proof development},
ISSN = {2150914x},
}
