@article{PORMA_1952__11_4_114710,
     author = {Bergmann, Gustav},
     title = {Multiplicative closures},
     journal = {Portugaliae mathematica},
     pages = {169--172},
     publisher = {mathdoc},
     volume = {11},
     number = {4},
     year = {1952},
     mrnumber = {0052391},
     zbl = {0048.02203},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1952__11_4_114710/}
}