TY - JOUR TI - [unknown] JO - Acta mathematica Universitatis Comenianae PY - 1980 SP - 93 EP - 108 VL - 37 PB - mathdoc UR - http://geodesic.mathdoc.fr/item/AMUC_1980__37_185786/ ID - AMUC_1980__37_185786 ER -