Alexandrov, George. “On the Three-Spaces Problem and Extension of MLUR Norms on Banach Spaces”. Ann. Sofia Univ. Fac. Math. and Inf. 86, no. 1 (December 12, 1994): 43–48. Accessed November 22, 2024. https://ftl5.uni-sofia.bg/index.php/fmi/article/view/436.