@article{VMUMM_1991_6_a1,
     author = {Yu. V. Egorov and V. A. Kondratiev},
     title = {Estimation of the first eigenvalue of the {Sturm{\textendash}Liouville} operator},
     journal = {Vestnik Moskovskogo universiteta. Matematika, mehanika},
     pages = {5--11},
     year = {1991},
     number = {6},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VMUMM_1991_6_a1/}
}