[1]
N. A. Izobov, “On the countability of the number of solutions of a two-dimensional linear Pfaff system with different characteristic sets”, Ukr. Mat. Zhurn., vol. 59, no. 2, pp. 172–189, Feb. 2007, Accessed: Dec. 06, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/3302