This excerpt taken from the C 10-K filed Feb 23, 2007.
(18) Merger of Terms.
This letter describes CGMIs/GCIBs offer of employment. Any other documents, discussions or agreements that you may have had with us are not part of our offer unless they are described in these Terms, including CGMI/GCIBs Principles of Employment which you must read carefully, sign and return as part of accepting our offer. These Terms and the Principles of Employment may not be modified except by another written agreement signed by both you and CGMI/GCIB.