Constructing free products of cyclic subgroups inside the group of units of integral group rings

It has been proved in Janssens, Jespers, and Temmerman [Proc. Amer. Math. Soc. 145 (2017), pp. 2771–2783] that if h is an element of prime order p in a finite nilpotent group G and u=h+(h-1)g\widehat {h}\in \mathbb {Z}G, u\not \in G, then \langle u^*,u\rangle \approx C_p\ast C_p. We offer a simple geometric approach to generalize this result.