GabrielР., NazarovaL. A., RoiterA. V., SergeychukV. V., and VossieckD. 1993. “Tame and Wild Subspace Problems”. Ukrains’kyi Matematychnyi Zhurnal 45 (3), 313–352. https://umj.imath.kiev.ua/index.php/umj/article/view/5815.