TY - JOUR TI - [unknown] JO - Acta mathematica Universitatis Comenianae PY - 1987 SP - 225 EP - 242 VL - 48-49 PB - mathdoc UR - http://geodesic.mathdoc.fr/item/AMUC_1987__48-49_185945/ ID - AMUC_1987__48-49_185945 ER -