@article{SM_2019_210_12_a1,
     author = {I. S. Vorob'ev and A. V. Ustinov},
     title = {Symmetric semigroups with three generators},
     journal = {Sbornik. Mathematics},
     pages = {1690--1701},
     year = {2019},
     volume = {210},
     number = {12},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_2019_210_12_a1/}
}