@article{GDZPPN002344955, title = {A generalization of Courant's nodal domain theorem..}, journal = {Mathematica Scandinavica}, volume = {5}, year = {1957}, pages = {15-20}, zbl = {0077.30101}, url = {http://dml.mathdoc.fr/item/GDZPPN002344955} }
PEETRE, JAAK. A generalization of Courant's nodal domain theorem... Mathematica Scandinavica, Tome 5 (1957) pp. 15-20. http://gdmltest.u-ga.fr/item/GDZPPN002344955/