@article{10_4153_CJM_1979_045_0,
     author = {Allegretto, Walter},
     title = {Lower {Bounds} on the {Number} of {Points} in the {Lower} {Spectrum} of {Elliptic} {Operators}},
     journal = {Canadian journal of mathematics},
     pages = {419--426},
     year = {1979},
     volume = {31},
     number = {2},
     doi = {10.4153/CJM-1979-045-0},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1979-045-0/}
}