SlyusarchukV. Y. “Denseness of the Set of Cauchy Problems With Nonunique Solutions in the Set of All Cauchy Problems”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 64, no. 7, July 2012, pp. 1001-6, https://umj.imath.kiev.ua/index.php/umj/article/view/2635.