Infra-Solvmanifolds and Rigidity of Subgroups in Solvable Linear   Algebraic Groups
  We give a new proof that compact infra-solvmanifolds with isomorphic fundamental groups are smoothly diffeomorphic. More generally, we prove rigidity results for manifolds which are constructed using affine actions of virtually polycyclic groups on solvable Lie groups. Our results are derived from rigidity properties of subgroups in solvable linear algebraic groups. 
Oliver Baues