@article{10_21136_CMJ_1977_101454,
     author = {Zelinka, Bohdan},
     title = {Tolerance relations on periodic commutative semigroups},
     journal = {Czechoslovak Mathematical Journal},
     pages = {167--169},
     publisher = {mathdoc},
     volume = {27},
     number = {1},
     year = {1977},
     doi = {10.21136/CMJ.1977.101454},
     mrnumber = {0427509},
     zbl = {0359.20045},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CMJ.1977.101454/}
}