@article{ Solr-acta12501, title = {On the interaction between closure operations and choice functions with applications to relational databases}, series = {Acta cybernetica}, author = {Demetrovics János}, year = {1992}, url = {http://acta.bibl.u-szeged.hu/12501/1/cybernetica_010_numb_003_129-139.pdf} }