Meduna, Alexander, and A. Gopalaratnam. “On Semi-Conditional Grammars With Productions Having Either Forbidding or Permitting Conditions”. Acta Cybernetica 11, no. 4 (January 1, 1994): 307-323. Accessed November 28, 2024. https://cyber.bibl.u-szeged.hu/index.php/actcybern/article/view/3435.