@book{UBHD-1029281, title={§§ 20, 21}, edition={3. Aufl.}, publisher={Heymann}, address={K{\"o}ln}, year={1978}, pages={323 S.}, language={ger}, isbn={3-452-17435-2 and 978-3-452-17435-2}, library={UB [Signatur: 2010 C 4021::10] ; GW [Signatur: GW/PE 750 M947(3)]}, }