Masahiro Iwano "On a general solution of a nonlinear $2$-system of the form $x^{2}dw/dx=Łambda w+xh(x,\,w)$ with a constant diagonal matrix $Łambda $ of signature $(1,\,1)$," Tohoku Mathematical Journal, Tohoku Math. J. (2) 32(4), 453-486, (1980)