@article{DE_1992_28_6_a13,
     author = {S. E. Zhelezovsky},
     title = {A dual variational principle for the wave equation},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1033--1039},
     publisher = {mathdoc},
     volume = {28},
     number = {6},
     year = {1992},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1992_28_6_a13/}
}