“On Local Asymptotic Expansions of Singularly Perturbed Systems of Differential Equations With a Degeneration in a Point”. Neliniini Kolyvannya 12, no. 2 (June 29, 2009): 279–285. Accessed January 21, 2026. https://twinhead.imath.kiev.ua/index.php/nosc/article/view/525.