@article{GDZPPN002081237,
title = {Coordinate free definitions of cross ratio.},
journal = {Elemente der Mathematik},
volume = {40},
year = {1985},
pages = {63-68},
zbl = {0569.51003},
url = {http://dml.mathdoc.fr/item/GDZPPN002081237}
}
Simonis, J.; van de Craats, J. de. Coordinate free definitions of cross ratio.. Elemente der Mathematik, Tome 40 (1985) pp. 63-68. http://gdmltest.u-ga.fr/item/GDZPPN002081237/