@article{700619,
     title = {Fredholm points of compactly perturbed bounded linear operators},
     booktitle = {General topology and its relations to modern analysis and algebra IV},
     series = {GDML\_Books},
     publisher = {Society of Czechoslovak Mathematicians and Physicist},
     address = {Praha},
     year = {1977},
     pages = {[268]-275},
     mrnumber = {MR0512712},
     zbl = {0385.47004},
     url = {http://dml.mathdoc.fr/item/700619}
}

Marek, I. Fredholm points of compactly perturbed bounded linear operators, dans General topology and its relations to modern analysis and algebra IV, GDML_Books,  (1977), pp. [268]-275. http://gdmltest.u-ga.fr/item/700619/