All communications hereunder will be in writing and effective only on receipt, and, if sent to the Representative, will be mailed, delivered or telefaxed to the Citigroup General Counsel (fax no.: (646) 291-1469) and confirmed to Citigroup at 388 Greenwich Street, New York, New York 10013, Attention: General Counsel; or, if sent to the Company, will be mailed, delivered or telefaxed to 972-556-6119 and confirmed to it at 6555 Sierra Drive, Irving, Texas 75039, attention of the Legal Department.