@unpublished{ClausDeckerKoschigetal.2015,
  author  = {Stephan Claus and Eva Decker and Robert Koschig and Barbara Meier},
  title   = {Mathe-{\"U}ben in Studium und Abitur},
  institution = {Zentrale Einrichtungen},
  year    = {2015},
  language  = {de}
}