@article{GDZPPN00206197X, title = {Eigenfunctions and Nodal Sets}, journal = {Commentarii mathematici Helvetici}, volume = {51}, year = {1976}, pages = {43-56}, zbl = {0334.35022}, url = {http://dml.mathdoc.fr/item/GDZPPN00206197X} }
Cheng, Shiu-Yuen. Eigenfunctions and Nodal Sets. Commentarii mathematici Helvetici, Tome 51 (1976) pp. 43-56. http://gdmltest.u-ga.fr/item/GDZPPN00206197X/