@article{RM_1964_19_4_a1,
     author = {A. S. Markus},
     title = {The eigen- and singular values of the sum and product of linear operators},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {91--120},
     publisher = {mathdoc},
     volume = {19},
     number = {4},
     year = {1964},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RM_1964_19_4_a1/}
}