@Article{Aehlig04,
  author =       {Aehlig, Klaus},
  title =        {Induction and Inductive Definitions in Fragments of Second Order Arithmetic},
  journal =      {The Journal of Symbolic Logic},
  year =         2005,
  volume =       70,
  number =        4,
  pages =        {1087--1107},
  month =        dec
}