@article{Jahnke2000,
  author    = {Jahnke, Thomas},
  title     = {Die vierte Dimension},
  year      = {2000},
  language  = {de}
}
@article{Jahnke2000,
  author    = {Jahnke, Thomas},
  title     = {Normaler, produktiver Mathematikunterricht},
  year      = {2000},
  language  = {de}
}