@article{ADM_2004_3_a5,
     author = {A. A. Kyrychenko and Yu. S. Samoilenko},
     title = {On the spectrum and spectrum multiplicities of a~sum of orthogonal projections},
     journal = {Algebra and discrete mathematics},
     pages = {71--76},
     publisher = {mathdoc},
     number = {3},
     year = {2004},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ADM_2004_3_a5/}
}