Zernov, A. E., and Yu. V. Kuzina. 2003. “Qualitative Investigation of the Singular Cauchy Problem <em class="a-Plus-plus">F</em>(<em class="a-Plus-plus">t</em>, <em class="a-Plus-plus">x</em>, <em class="a-Plus-plus">x</em>′) = 0, <em class="a-Plus-plus">x</Em&gt;(0) = 0”. Ukrains’kyi Matematychnyi Zhurnal 55 (12), 1720-23. https://umj.imath.kiev.ua/index.php/umj/article/view/4033.