@article{Bartels2003,
  author    = {Bartels, Knut},
  title     = {Evaluation of online exercises with free text input},
  isbn      = {3-8322-1977-3},
  year      = {2003},
  language  = {en}
}
@article{Bartels2002,
  author    = {Bartels, Knut},
  title     = {E-stat : automatic evaluation of online exercises},
  year      = {2002},
  language  = {en}
}