Free-by-Demushkin pro-p groups

Abstract

We give an example of a short exact sequence 1→N→G→D→1 of pro-p groups such that the cohomological dimension cd(G)=2, G is (topologically) finitely generated, N is a free pro-p group of infinite rank, D is a Demushkin group, for every closed subgroup S of G containing N and any natural number n the inflation map Open image in new window is an isomorphism but G is not a free pro-p product of a free pro-p group by a Demushkin group. This is a group theoretic version of a question raised by T. Wurfel for some special Galois groups.