TY - JOUR TI - [unknown] JO - Acta mathematica Universitatis Comenianae PY - 1983 SP - 215 EP - 218 VL - 42-43 PB - mathdoc UR - http://geodesic.mathdoc.fr/item/AMUC_1983__42-43_185859/ ID - AMUC_1983__42-43_185859 ER -