Demetrovics, János, Gusztáv Hencsey, Leonid O. Libkin, and Ilya Muchnik. “Normal Form Relation Schemes : A New Characterization”. Acta Cybernetica 10, no. 3 (January 1, 1992): 141–153. Accessed May 9, 2025. https://cyber.bibl.u-szeged.hu/index.php/actcybern/article/view/3402.