@article{TMF_1990_84_2_a1,
     author = {S. V. Ketov and K. E. Osetrin and Ya. S. Prager},
     title = {Geometry of~dual two-dimensional nonlinear $\sigma$~models},
     journal = {Teoreti\v{c}eska\^a i matemati\v{c}eska\^a fizika},
     pages = {173--180},
     publisher = {mathdoc},
     volume = {84},
     number = {2},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TMF_1990_84_2_a1/}
}