Donald Duck asks Mickey Mouse if it is okay if Donald stays overnight in Mickey's Birthday Land, which is real property owned by Mickey. Mickey says "no problem" and he hands the keys over to Donald. Later in the day, Mickey changes his mind and asks Donald for the keys and tells him he may not stay there overnight. Does Donald have to give back the keys and leave Mickey's Birthday Land?

Walker, Texas Ranger orally grants GI Joe an easement to practice military maneuvers on Walker's ranch in Texas in perpetuity. What kind of an interest does Joe have in Walker's property?

Walker, Texas Ranger orally grants GI Joe permission to practice military maneuvers on Walker's ranch in Texas. Because of this promise, Joe moves from Illinois to Texas to be near the ranch. Later, Walker changes his mind and wants to revoke his permission. What is Joe's best legal argument to prevent this revocation?