TY - JOUR TI - [unknown] JO - Acta mathematica Universitatis Comenianae PY - 1983 SP - 255 EP - 270 VL - 42-43 PB - mathdoc UR - http://geodesic.mathdoc.fr/item/AMUC_1983__42-43_185863/ ID - AMUC_1983__42-43_185863 ER -