@article{10_21136_CMJ_1989_102295,
     author = {\v{S}lapal, Josef},
     title = {On relations},
     journal = {Czechoslovak Mathematical Journal},
     pages = {198--214},
     publisher = {mathdoc},
     volume = {39},
     number = {2},
     year = {1989},
     doi = {10.21136/CMJ.1989.102295},
     mrnumber = {992127},
     zbl = {0682.04001},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CMJ.1989.102295/}
}