@article{SF_1991__43_3_135108,
     author = {P.A. Grillet},
     title = {Nilsemigroups on trees.},
     journal = {Semigroup forum},
     pages = {187--201},
     publisher = {mathdoc},
     volume = {43},
     number = {3},
     year = {1991},
     zbl = {0744.20050},
     url = {http://geodesic.mathdoc.fr/item/SF_1991__43_3_135108/}
}