@article{LJM_2005_18_a4,
     author = {P. K. Jakobsen and V. V. Lychagin},
     title = {Universal semigroups},
     journal = {Lobachevskii journal of mathematics},
     pages = {107--125},
     publisher = {mathdoc},
     volume = {18},
     year = {2005},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/LJM_2005_18_a4/}
}