@article{JAC_2009__29_1_a4,
     author = {Guo, Li},
     title = {Operated semigroups, {Motzkin} paths and rooted trees},
     journal = {Journal of Algebraic Combinatorics},
     pages = {35--62},
     publisher = {mathdoc},
     volume = {29},
     number = {1},
     year = {2009},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/JAC_2009__29_1_a4/}
}