Rav held that a thief repays a stolen item based on the price of the item at the time of the theft and the double payment and the four/five times payment based on the price at the judgment. Rav Sheshet raises two difficulties against Rav from braitot, but they are resolved. Rav's ruling is limited after resolving the difficulties. A braita is brought in support of Rav, but Rava rejects the proof. Rabbi Il'ah rules on the payment in a case where an animal was stolen as a calf but becomes a grown animal before the payment. Rabbi Chanina raises a difficulty on Rabbi Il'ah's ruling from a braita. What is the basis of their disagreement?