Bel’skiiD. V., and PelyukhG. P. “On the Behavior of Solutions of Linear Functional Differential Equations With Constant Coefficients and Linearly Transformed Argument in Neighborhoods of Singular Points”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 57, no. 12, Dec. 2005, pp. 1668–1676, https://umj.imath.kiev.ua/index.php/umj/article/view/3717.