@article{SLC_1989_22_a8,
     author = {Pavel Goralcik},
     title = {Avoidable {Words} and {Lattice} {Universal} {Semigroup} {Varieties}},
     journal = {S\'eminaire lotharingien de combinatoire},
     publisher = {mathdoc},
     volume = {22},
     year = {1989},
     url = {http://geodesic.mathdoc.fr/item/SLC_1989_22_a8/}
}