@article{10_4064_sm_97_3_227_238,
     author = {Jan Stochel},
     title = {Characterizations of subnormal operators},
     journal = {Studia Mathematica},
     pages = {227--238},
     publisher = {mathdoc},
     volume = {97},
     number = {3},
     year = {1990},
     doi = {10.4064/sm-97-3-227-238},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/sm-97-3-227-238/}
}