BGB §§ 13, 119 Abs. 1, § 123 Abs. 1, § 142 Abs. 1-2, §§ 242, 305 Abs. 1 S. 3, §§ 307, 310 Abs. 3-4, §§ 312, 355, 474 ff.; EGBGB Art. 170, 232 § 1, Art. 229 § 5