@article{1077489493,
author = {Downs, Jr., Thomas L.},
title = {Asymptotic lines through a planar point of a surface and lines of
curvature through an umbilic},
journal = {Duke Math. J.},
volume = {2},
number = {1},
year = {1936},
pages = { 415-422},
language = {en},
url = {http://dml.mathdoc.fr/item/1077489493}
}
Downs, Jr., Thomas L. Asymptotic lines through a planar point of a surface and lines of
curvature through an umbilic. Duke Math. J., Tome 2 (1936) no. 1, pp. 415-422. http://gdmltest.u-ga.fr/item/1077489493/