@article{10_4153_CMB_1960_010_3,
     author = {Beesack, Paul R.},
     title = {Elementary {Proofs} of the {Extremal} {Properties} of the {Eigenvalues} of the {Sturm-Liouville} {Equation}},
     journal = {Canadian mathematical bulletin},
     pages = {59--77},
     year = {1960},
     volume = {3},
     number = {1},
     doi = {10.4153/CMB-1960-010-3},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1960-010-3/}
}