@article{GDZPPN001254235,
title = {The Hopf property and K-free products of semigroups.},
journal = {Semigroup forum},
volume = {20},
year = {1980},
pages = {343-368},
zbl = {0448.20055},
url = {http://dml.mathdoc.fr/item/GDZPPN001254235}
}
Jones, P.R. The Hopf property and K-free products of semigroups.. Semigroup forum, Tome 20 (1980) pp. 343-368. http://gdmltest.u-ga.fr/item/GDZPPN001254235/