TY - JOUR TI - [unknown] JO - Acta mathematica Universitatis Comenianae PY - 1981 SP - 129 EP - 168 VL - 38 PB - mathdoc UR - http://geodesic.mathdoc.fr/item/AMUC_1981__38_185799/ ID - AMUC_1981__38_185799 ER -