@article{JAC_1993__2_2_a4,
     author = {Butler, Lynne M. and Hales, Alfred W.},
     title = {Nonnegative {Hall} polynomials},
     journal = {Journal of Algebraic Combinatorics},
     pages = {125--135},
     publisher = {mathdoc},
     volume = {2},
     number = {2},
     year = {1993},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/JAC_1993__2_2_a4/}
}