TY - JOUR TI - On the closedness of nilpotent DR tree languages under Boolean operations T3 - Acta cybernetica AU - GĂ©cseg Ferenc PY - 2006 LA - English SN - 0324-721X UR - http://acta.bibl.u-szeged.hu/12775/1/Gecseg_2006_ActaCybernetica.pdf ER -