Acme Co. offers to buy 1000 widgets from Widget World Co. The written offer provides for 1000 at $10 per widget, to be delivered May 1. The offer has no other provisions. Widget World sends a written acceptance. However, the acceptance also states that if any claim arises under this contract, Widget World must be notified within 10 days. Acme does not object to this provision. Both parties are merchants. Which of the following best describes this situation?