Zernov, A. E. 2003. “Qualitative Investigation of the Singular Cauchy Problem $\sum\limits_{k = 1}^n {(a_{k1} T + a_{k2} x)(x’)^k = b_1 T + b_2 X + f(t,x,x’),x(0) = 0}$”. Ukrains’kyi Matematychnyi Zhurnal 55 (10), 1419-24. https://umj.imath.kiev.ua/index.php/umj/article/view/4010.