@article{CMUC_1980__21_3_a3,
     author = {Drbohlav, Karel},
     title = {Remarks on tolerance semigroups},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {447--456},
     publisher = {mathdoc},
     volume = {21},
     number = {3},
     year = {1980},
     mrnumber = {590125},
     zbl = {0444.20059},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1980__21_3_a3/}
}