An algebraic structure of groups of solutions of the third Aczel-Jabotinsky formal differential equation

Abstract

We study the algebraic structure of the groups of solutions of the third Acz{\'e}l-Jabotinsky differential equation $(H\circ \Phi)(x)=\frac{d\Phi}{d x}\cdot H(x)$ in the rings of formal power series and truncated formal power series $k[[x]]_s$, where $s$ is either a positive integer or $s=\infty$ and $H\in k[[x]]_s$ is given. We give also the detailed description of all solutions of this equation.