Free groups and semigroups in ßN.
Semigroup forum, Tome 30 (1984), pp. 177-194
@article{SF_1984__30_134714,
author = {N. Hindman and J. Pym},
title = {Free groups and semigroups in {{\ss}N.}},
journal = {Semigroup forum},
pages = {177--194},
year = {1984},
volume = {30},
zbl = {0536.22005},
url = {http://geodesic.mathdoc.fr/item/SF_1984__30_134714/}
}
N. Hindman; J. Pym. Free groups and semigroups in ßN.. Semigroup forum, Tome 30 (1984), pp. 177-194. http://geodesic.mathdoc.fr/item/SF_1984__30_134714/