@article{MalettiGraehlHopkinsetal.2009,
  author    = {Andreas Maletti and Jonathan Graehl and Mark Hopkins and Kevin Knight},
  title     = {The power of extended top-down tree transducers},
  doi       = {10.1137/070699160},
  url       = {http://epubs.siam.org/SICOMP/},
  year      = {2009},
}