@article{SF_1989__39_2_134985,
     author = {T. Saito},
     title = {Products of four idempotents in finite full transformation semigroups.},
     journal = {Semigroup forum},
     pages = {179--194},
     publisher = {mathdoc},
     volume = {39},
     number = {2},
     year = {1989},
     zbl = {0671.20061},
     url = {http://geodesic.mathdoc.fr/item/SF_1989__39_2_134985/}
}