@article{GDZPPN001259075,
title = {Subprincipal closed ideals in \ss N.},
journal = {Semigroup forum},
volume = {36},
year = {1987},
pages = {223-246},
zbl = {0659.22002},
url = {http://dml.mathdoc.fr/item/GDZPPN001259075}
}
Hindman, N.; Davenport, D. Subprincipal closed ideals in ßN.. Semigroup forum, Tome 36 (1987) pp. 223-246. http://gdmltest.u-ga.fr/item/GDZPPN001259075/