“The density of the set of unsolvable Cauchy problems in the set of all Cauchy problems for an infinite-dimensional Banach space”, НК, vol. 5, no. 1, pp. 86–89, Mar. 2002, Accessed: Jan. 22, 2026. [Online]. Available: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/203