@article{CMUC_1998__39_3_a4,
     author = {Lemmert, Roland and Volkmann, Peter},
     title = {On the positivity of semigroups of operators},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {483--489},
     publisher = {mathdoc},
     volume = {39},
     number = {3},
     year = {1998},
     mrnumber = {1666770},
     zbl = {0970.47026},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1998__39_3_a4/}
}