@article{MZM_1991_50_4_a13,
     author = {\`E. L. Pekarev},
     title = {Extreme subsets of operator intervals},
     journal = {Matemati\v{c}eskie zametki},
     pages = {96--101},
     year = {1991},
     volume = {50},
     number = {4},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1991_50_4_a13/}
}