@article{10_4171_dm_652,
     author = {Bernard Helffer and Pierre H. B\'erard},
     title = {On {Courant's} {Nodal} {Domain} {Property} for {Linear} {Combinations} of {Eigenfunctions.} {I}},
     journal = {Documenta mathematica},
     pages = {1561--1585},
     year = {2018},
     volume = {23},
     doi = {10.4171/dm/652},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/dm/652/}
}