@article{SF_1992__45_3_135191,
     author = {G.M.S. Gomes and J.M. Howie},
     title = {On the ranks of certain semigroups of order-preserving  transformations.},
     journal = {Semigroup forum},
     pages = {272--282},
     publisher = {mathdoc},
     volume = {45},
     number = {3},
     year = {1992},
     zbl = {0769.20029},
     url = {http://geodesic.mathdoc.fr/item/SF_1992__45_3_135191/}
}