@article{SF_1993__46_1_135218,
     author = {A. de Luca and S. Varricchio},
     title = {On a conjecture of {Brown.}},
     journal = {Semigroup forum},
     pages = {116--119},
     publisher = {mathdoc},
     volume = {46},
     number = {1},
     year = {1993},
     zbl = {0791.20066},
     url = {http://geodesic.mathdoc.fr/item/SF_1993__46_1_135218/}
}