@article{GDZPPN00220648X,
title = {On the nodal line of the second eigenfunction of elliptic operators in two dimensions.},
journal = {Journal f\"ur die reine und angewandte Mathematik},
volume = {394},
year = {1989},
pages = {1-13},
zbl = {0658.35068},
url = {http://dml.mathdoc.fr/item/GDZPPN00220648X}
}
Ruf, Bernhard; Kappeler, Th. On the nodal line of the second eigenfunction of elliptic operators in two dimensions.. Journal für die reine und angewandte Mathematik, Tome 394 (1989) pp. 1-13. http://gdmltest.u-ga.fr/item/GDZPPN00220648X/