@article{GDZPPN001262289, title = {Some closure properties in monoids.}, journal = {Semigroup forum}, volume = {46}, year = {1993}, pages = {73-77}, zbl = {0776.20022}, url = {http://dml.mathdoc.fr/item/GDZPPN001262289} }
Schanuel, S.; Isbell, J. Some closure properties in monoids.. Semigroup forum, Tome 46 (1993) pp. 73-77. http://gdmltest.u-ga.fr/item/GDZPPN001262289/