@article{10_4064_sm_65_1_21_29,
     author = {Andrzej Pokrzywa},
     title = {Method of orthogonal projections and approximation of the spectrum of a bounded operator},
     journal = {Studia Mathematica},
     pages = {21--29},
     publisher = {mathdoc},
     volume = {65},
     number = {1},
     year = {1979},
     doi = {10.4064/sm-65-1-21-29},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/sm-65-1-21-29/}
}