ABC Inc., the owner of the registered trademark Tony's Donut House (for the retail sale of baked goods) writes a letter to XYZ Co. indicating that ABC objects to XYZ's use of Bill's Donut Shop (for the retail sale of baked goods) and states that it is reviewing the matter and will contact XYZ. XYZ then spends significant sums of money in promoting its mark and services. Three years after the date of the letter, ABC sues XYZ for trademark infringement. What defenses should XYZ assert?