@article{10_1017_S0017089501010035,
     author = {Niechwiej, Jan},
     title = {Two conditions for subnormality of unbounded operators},
     journal = {Glasgow mathematical journal},
     pages = {23--28},
     year = {2001},
     volume = {43},
     number = {1},
     doi = {10.1017/S0017089501010035},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089501010035/}
}