@article{MZ_1982__179_173141,
     author = {Peter Hess},
     title = {On the {Principal} {Eigenvalue} of a {Second} {Order} {Linear} {Elliptic} {Problem} with an {Indefinite} {Weight} {Function.}},
     journal = {Mathematische Zeitschrift},
     pages = {237--240},
     year = {1982},
     volume = {179},
     zbl = {0461.35066},
     url = {http://geodesic.mathdoc.fr/item/MZ_1982__179_173141/}
}