@article{MAN_1981__258_163611,
     author = {Peter Hess and Stefan Senn},
     title = {On {Positive} {Solutions} of a {Linear} {Elliptic} {Eigenvalue} {Problem} with {Neumann} {Boundary} {Conditions.}},
     journal = {Mathematische Annalen},
     pages = {459--470},
     publisher = {mathdoc},
     volume = {258},
     year = {1981},
     zbl = {0485.35042},
     url = {http://geodesic.mathdoc.fr/item/MAN_1981__258_163611/}
}