@article{GDZPPN001251759, title = {Right PP monoids with central idempotents.}, journal = {Semigroup forum}, volume = {12}, year = {1976}, pages = {229-238}, zbl = {0353.20051}, url = {http://dml.mathdoc.fr/item/GDZPPN001251759} }
Fountain, J. Right PP monoids with central idempotents.. Semigroup forum, Tome 12 (1976) pp. 229-238. http://gdmltest.u-ga.fr/item/GDZPPN001251759/