@article{ISU_2012_12_1_a4,
     author = {M. Yu. Romanova},
     title = {About numerical range of semigroup's generator},
     journal = {Izvestiya of Saratov University. Mathematics. Mechanics. Informatics},
     pages = {29--32},
     publisher = {mathdoc},
     volume = {12},
     number = {1},
     year = {2012},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ISU_2012_12_1_a4/}
}