@article{VYURM_2014_6_1_a4,
     author = {M. L. Katkov},
     title = {Concept extension for concave operator},
     journal = {Vestnik \^U\v{z}no-Uralʹskogo gosudarstvennogo universiteta. Seri\^a, Matematika, mehanika, fizika},
     pages = {28--29},
     publisher = {mathdoc},
     volume = {6},
     number = {1},
     year = {2014},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VYURM_2014_6_1_a4/}
}