@article{10_1017_S0017089502001027,
     author = {AIENA, PIETRO and GONZ\'ALEZ, MANUEL and MARTIN\'ON, ANTONIO},
     title = {ON {THE} {PERTURBATION} {CLASSES} {OF} {CONTINUOUS} {SEMI-FREDHOLM} {OPERATORS}},
     journal = {Glasgow mathematical journal},
     pages = {91--95},
     year = {2003},
     volume = {45},
     number = {1},
     doi = {10.1017/S0017089502001027},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089502001027/}
}