We show that if H is a commensurated subgroup of G such that both H and G are of type V F P and vcd ( G ) = vcd ( H ) + 1 , then G is the fundamental group of a graph of groups in which all vertex and edge groups are commensurable to H . We also investigate commensurated subgroups of one-relator groups and duality groups.
Alexander Margolis (Thu,) studied this question.