Ger, Joanna. “On Analytic Solutions of the Equation ϕ(f(x)) = g(x,ϕ(x)) (III)”. Annales Mathematicae Silesianae, vol. 1, Sept. 1985, pp. 93-102, https://trrest.vot.pl/ojsus/index.php/AMSIL/article/view/14339.