TY - JOUR TI - [unknown] JO - Acta mathematica Universitatis Comenianae PY - 1983 SP - 249 EP - 254 VL - 42-43 PB - mathdoc UR - http://geodesic.mathdoc.fr/item/AMUC_1983__42-43_185862/ ID - AMUC_1983__42-43_185862 ER -