@article{10_4153_CJM_1978_025_2,
     author = {Brown, R. C.},
     title = {Differential {Operators} with {Abstract} {Boundary} {Conditions}},
     journal = {Canadian journal of mathematics},
     pages = {262--288},
     year = {1978},
     volume = {30},
     number = {2},
     doi = {10.4153/CJM-1978-025-2},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1978-025-2/}
}