@article{DOCMA_2018__23__a20,
     author = {B\'erard, Pierre H. and Helffer, Bernard},
     title = {On {Courant's} {Nodal} {Domain} {Property} for {Linear} {Combinations} of {Eigenfunctions.} {I}},
     journal = {Documenta mathematica},
     pages = {1561--1585},
     publisher = {mathdoc},
     volume = {23},
     year = {2018},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/DOCMA_2018__23__a20/}
}