@article{IM2_1976_10_2_a7,
     author = {\`E. L. Pekarev and Yu. L. Shmul'yan},
     title = {Parallel addition and parallel subtraction of operators},
     journal = {Izvestiya. Mathematics},
     pages = {351--370},
     year = {1976},
     volume = {10},
     number = {2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1976_10_2_a7/}
}