@article{CMH_1979__54_139799,
     author = {Shmuel Friedland},
     title = {Extremal eigenvalue problems defined on conformal classes of compact {Riemannian} manifolds.},
     journal = {Commentarii mathematici Helvetici},
     pages = {494--507},
     publisher = {mathdoc},
     volume = {54},
     year = {1979},
     zbl = {0418.58017},
     url = {http://geodesic.mathdoc.fr/item/CMH_1979__54_139799/}
}