@article{10_1090_S0894_0347_2010_00676_5,
     author = {Hansen, Anders},
     title = {On the {Solvability} {Complexity} {Index,} the {\dh}‘›-pseudospectrum and approximations of spectra of operators},
     journal = {Journal of the American Mathematical Society},
     pages = {81--124},
     publisher = {mathdoc},
     volume = {24},
     number = {1},
     year = {2011},
     doi = {10.1090/S0894-0347-2010-00676-5},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S0894-0347-2010-00676-5/}
}