@article{10_1017_S0017089500005474,
     author = {Lambert, Alan},
     title = {A characterization of subnormal operators},
     journal = {Glasgow mathematical journal},
     pages = {99--101},
     year = {1984},
     volume = {25},
     number = {1},
     doi = {10.1017/S0017089500005474},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089500005474/}
}