Lohrey, Markus. “NP-Completeness Results Concerning the Transformation of Logic Programs into Attribute Grammars”. Acta Cybernetica 13, no. 3 (January 1, 1998): 209–224. Accessed May 11, 2025. https://cyber.bibl.u-szeged.hu/index.php/actcybern/article/view/3488.