@article{CMH_1990__65_3_140185,
     author = {Rolf P\"utter},
     title = {On the nodal lines of second eigenfunctions of the fixed membrane problem.},
     journal = {Commentarii mathematici Helvetici},
     pages = {96--103},
     publisher = {mathdoc},
     volume = {65},
     number = {3},
     year = {1990},
     zbl = {0705.35003},
     url = {http://geodesic.mathdoc.fr/item/CMH_1990__65_3_140185/}
}