@article{SF_1989__39_2_134980,
     author = {J. Justin and G. Pirillo},
     title = {Comments on the permutation property for semigroups.},
     journal = {Semigroup forum},
     pages = {109--112},
     publisher = {mathdoc},
     volume = {39},
     number = {2},
     year = {1989},
     zbl = {0665.20028},
     url = {http://geodesic.mathdoc.fr/item/SF_1989__39_2_134980/}
}