§§ 241 Abs. 2, 433 BGB; §§ 253, 91a ZPO; Art. 13 GG; §§ 9 Satz 3, 11 Abs. 3, 19 Abs. 2, 17 GasGVV; §§ 24 Abs. 3, 21 Satz 1 NDAV