@article{10_4153_CJM_1978_096_4,
     author = {Berg, I. D.},
     title = {Index {Theory} for {Perturbations} of {Direct} {Sums} of {Normal} {Operators} and {Weighted} {Shifts}},
     journal = {Canadian journal of mathematics},
     pages = {1152--1165},
     year = {1978},
     volume = {30},
     number = {6},
     doi = {10.4153/CJM-1978-096-4},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1978-096-4/}
}