A geometric approach to temptation

We provide a simple geometric proof of the Gul and Pesendorfer's (Gul and Pesendorfer, 2001) utility representation theorem about choice under temptation without self-control. We extract two incomplete orders from preferences: temptation relation and resistance relation. We characterize those relations geometrically and obtain temptation utility using a separation method à la Aumann (Aumann, 1962).