@article{SF_1993__46_1_135244,
     author = {D. Mittenhuber},
     title = {Semigroups in the simply connected  covering of {SL(2).}},
     journal = {Semigroup forum},
     pages = {379--387},
     publisher = {mathdoc},
     volume = {46},
     number = {1},
     year = {1993},
     zbl = {0776.22001},
     url = {http://geodesic.mathdoc.fr/item/SF_1993__46_1_135244/}
}