TY - JOUR TI - [unknown] JO - Acta mathematica Universitatis Comenianae PY - 1981 SP - 63 EP - 98 VL - 38 PB - mathdoc UR - http://geodesic.mathdoc.fr/item/AMUC_1981__38_185803/ ID - AMUC_1981__38_185803 ER -