@article{SF_1987__36_134899,
     author = {W. Ruppert},
     title = {In a left-topological semigroup with dense center the closure of any left ideal is an ideal.},
     journal = {Semigroup forum},
     pages = {247--248},
     publisher = {mathdoc},
     volume = {36},
     year = {1987},
     zbl = {0623.22004},
     url = {http://geodesic.mathdoc.fr/item/SF_1987__36_134899/}
}