RozhankovskayaM. I., and SyavavkoM. S. 1998. “Transformation of Formal Expansions of Solutions of Linear Differential Equations in a Parameter into Continued <em class="a-Plus-plus">RITZ</Em&gt;-Fractions”. Ukrains’kyi Matematychnyi Zhurnal 50 (5), 679–686. https://umj.imath.kiev.ua/index.php/umj/article/view/4906.