@article{CMUC_1963_4_1_a1,
     author = {Drbohlav, Karel},
     title = {Concerning congruence relations on commutative semigroups {(Preliminary} communication)},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {11--13},
     year = {1963},
     volume = {4},
     number = {1},
     mrnumber = {0158943},
     zbl = {0116.25503},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1963_4_1_a1/}
}