@book{Sperber2003,
  author    = {Christian Sperber},
  title     = {Hildegard von Bingen - eine widerst{\"a}ndige Frau},
  isbn      = {3-929303-25-6},
  url       = {http://www.magi-e.historicum.net/reihe/magi-e_band_06.pdf},
  year      = {2003},
}