Moskaleva, Yu. P., V. L. Ostrovskyi, and K. A. Yusenko. “On Quadruples of Linearly Connected Projections and Transitive Systems of Subspaces”. Methods of Functional Analysis and Topology 13, no. 1 (March 25, 2007): 43–49. Accessed December 16, 2025. https://zen.imath.kiev.ua/index.php/mfat/article/view/335.