The second bounded cohomology of hypo-Abelian groups

Fujiwara [K. Fujiwara, The second bounded cohomology of a group with infinitely many ends, math.GR/9505208] conjectured that the second bounded cohomology of a group is zero or infinite-dimensional as a vector space over R. However, it is known that there are some linear groups for which the second bounded cohomology is not zero but finite-dimensional. In this paper, by using the transfinitely extended derived series, we prove that Fujiwaraʹs conjecture is true for the hypo-Abelian groups, that is, groups with no non-trivial perfect subgroups.