TY - JOUR TI - [unknown] JO - Acta mathematica Universitatis Comenianae PY - 1985 SP - 131 EP - 136 VL - 46-47 PB - mathdoc UR - http://geodesic.mathdoc.fr/item/AMUC_1985__46-47_185910/ ID - AMUC_1985__46-47_185910 ER -