@article{SF_1976__12_134183,
     author = {P.G. Trotter},
     title = {Exponential ....-semigroups.},
     journal = {Semigroup forum},
     pages = {313--332},
     year = {1976},
     volume = {12},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SF_1976__12_134183/}
}