TY - JOUR AU - Šlapal, Josef TI - On the direct power of relational systems JO - Mathematica slovaca PY - 1989 SP - 251 EP - 255 VL - 39 IS - 3 PB - mathdoc UR - http://geodesic.mathdoc.fr/item/MASLO_1989__39_3_a3/ LA - en ID - MASLO_1989__39_3_a3 ER -