@article{MAN_1977__227_162974,
     author = {Palle E.T. Jorgensen},
     title = {Approximately {Invariant} {Subspaces} for {Unbounded} {Linear} {Operators.} {II.}},
     journal = {Mathematische Annalen},
     pages = {177--182},
     publisher = {mathdoc},
     volume = {227},
     year = {1977},
     zbl = {0345.47023},
     url = {http://geodesic.mathdoc.fr/item/MAN_1977__227_162974/}
}