@article{JIS_2004__7_3_a5,
     author = {Laradji,  A. and Umar,  A.},
     title = {Combinatorial results for semigroups of order-decreasing partial transformations},
     journal = {Journal of integer sequences},
     year = {2004},
     volume = {7},
     number = {3},
     zbl = {1064.05016},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/JIS_2004__7_3_a5/}
}