@article{PORMA_1959__18_4_114826,
     author = {Conrad, Paul},
     title = {Semigroups of real numbers},
     journal = {Portugaliae mathematica},
     pages = {199--201},
     publisher = {mathdoc},
     volume = {18},
     number = {4},
     year = {1959},
     mrnumber = {0125167},
     zbl = {0098.01702},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1959__18_4_114826/}
}