@article{MAN_1990__287_1_164680,
     author = {Yoshihiro Nakamura and Nobuhisa Sakakibara},
     title = {Perfectness of certain subsemigroups of a perfect semigroup.},
     journal = {Mathematische Annalen},
     pages = {213--220},
     year = {1990},
     volume = {287},
     number = {1},
     zbl = {0675.20055},
     url = {http://geodesic.mathdoc.fr/item/MAN_1990__287_1_164680/}
}