@article{10_21136_MB_1993_126020,
     author = {Jakub{\'\i}k, J\'an},
     title = {On directed groups with additional operations},
     journal = {Mathematica Bohemica},
     pages = {11--17},
     publisher = {mathdoc},
     volume = {118},
     number = {1},
     year = {1993},
     doi = {10.21136/MB.1993.126020},
     mrnumber = {1213828},
     zbl = {0799.06027},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/MB.1993.126020/}
}