ZERNOV, A. E.; KUZINA, Y. V. 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, v. 55, n. 12, p. 1720-1723, 25 Dec. 2003.