Gabriel Р., L. A. Nazarova, A. V. Roiter, V. V. Sergeychuk, and D. Vossieck, “Tame and wild subspace problems”, Ukr. Mat. Zhurn., vol. 45, no. 3, pp. 313–352, Mar. 1993, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/5815