@article{PORMA_1996__53_1_47476,
     author = {Umar, Abdullahi},
     title = {On the ranks of certain finite semigroups of order-decreasing transformations.},
     journal = {Portugaliae mathematica},
     pages = {23--34},
     publisher = {mathdoc},
     volume = {53},
     number = {1},
     year = {1996},
     zbl = {0844.20050},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1996__53_1_47476/}
}