@article{10_21136_CMJ_1989_102330,
     author = {Lai, C. K. and Shum, Kar-Ping},
     title = {Characterizations of dual semigroups},
     journal = {Czechoslovak Mathematical Journal},
     pages = {578--584},
     publisher = {mathdoc},
     volume = {39},
     number = {4},
     year = {1989},
     doi = {10.21136/CMJ.1989.102330},
     mrnumber = {1017989},
     zbl = {0698.20052},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CMJ.1989.102330/}
}