Donchev, Tzanko, and Iordan Slavov. “Singularly Perturbed Delayed Differential Inclusions”. Ann. Sofia Univ. Fac. Math. and Inf. 91 (December 12, 1999): 61–71. Accessed November 21, 2024. https://ftl5.uni-sofia.bg/index.php/fmi/article/view/269.