@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/