@article{DAN_1993_331_4_a11,
     author = {A. I. Propoi and A. V. Pukhlikov},
     title = {Quadratic approximation in nonlinear extremal problems},
     journal = {Doklady Akademii Nauk},
     pages = {425--427},
     publisher = {mathdoc},
     volume = {331},
     number = {4},
     year = {1993},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1993_331_4_a11/}
}