TY - JOUR AU - Hindman, N. AU - Davenport, D. TI - Subprincipal closed ideals in ßN. JO - Semigroup forum PY - 1987 VL - 36 SP - 223 EP - 246 KW - Stone-Cech compactification; Ramsey Theory; subprincipal closed ideals; upper, lower and Banach density UR - http://eudml.org/doc/134898 ER -