“The Density of the Set of Unsolvable Cauchy Problems in the Set of All Cauchy Problems for an Infinite-Dimensional Banach Space”. Neliniini Kolyvannya 5, no. 1 (March 29, 2002): 86–89. Accessed January 22, 2026. https://twinhead.imath.kiev.ua/index.php/nosc/article/view/203.