Abelian subgroups of \Out(F_n)
  We classify abelian subgroups of Out(F_n) up to finite index in an algorithmic and computationally friendly way. A process called disintegration is used to canonically decompose a single rotationless element \phi into a composition of finitely many elements and then use these elements to generate an abelian subgroup A(\phi) that contains \phi. The main theorem is that up to finite index every abelian subgroup is realized by this construction. As an application we classify, up to finite index, abelian subgroups of Out(F_n) and of IA with maximal rank. 
Mark Feighn and Michael Handel