Several contracts relating to the same matters, between the same parties, and made as parts of substantially one transaction, are to be taken together. Ca. Civ. Code § 1642 Enacted 1872.
The execution of a contract in writing, whether the law requires it to be written or not, supersedes all the negotiations or stipulations concerning its matter which preceded or accompanied the execution of the instrument. Ca. Civ. Code § 1625 Amended by Stats. 1905, Ch. 451.