Kühnemann, Armin, and Heiko Vogler. “A Pumping Lemma for Output Languages of Attributed Tree Transducers”. Acta Cybernetica 11, no. 4 (January 1, 1994): 261-305. Accessed April 26, 2024. https://cyber.bibl.u-szeged.hu/index.php/actcybern/article/view/3434.