@book{Hufnagel2010,
  author    = {Hufnagel, W.},
  title     = {Managementsysteme, LE 1},
  address   = {Hagen},
  year      = {2010},
  language  = {mul}
}
@book{HufnagelRueth2010,
  author    = {Hufnagel, W. and R{\"u}th, D.},
  title     = {Internes Rechnungswesen, LE 1-5},
  address   = {Hagen},
  year      = {2010},
  language  = {mul}
}