Further remarks on formal power series
Marcin Borkowski, Piotr Maćkowiak (2012)
Commentationes Mathematicae Universitatis Carolinae
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In this paper, we present a considerable simplification of the proof of a theorem by Gan and Knox, stating a sufficient and necessary condition for existence of a composition of two formal power series. Then, we consider the behavior of such series and their (formal) derivatives at the boundary of the convergence circle, obtaining in particular a theorem of Bugajewski and Gan concerning the structure of the set of points where a formal power series is convergent with all its derivatives. ...