@article{10_4153_CMB_1970_001_8,
     author = {Clements, John C.},
     title = {Enclosure {Theorems} for {Eigenvalues} of {Elliptic} {Operators}},
     journal = {Canadian mathematical bulletin},
     pages = {1--7},
     year = {1970},
     volume = {13},
     number = {1},
     doi = {10.4153/CMB-1970-001-8},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1970-001-8/}
}