(Mishnah): If a person exchanged a cow for a donkey and it gave birth; or if a person sold his slave-woman and she gave birth...

If the seller says that it happened before I sold it and the buyer says that it happened after I bought it - they divide it.

If a person had two slaves or two fields, one big and one small - if the buyer says that he bought the big one and the seller does not know, the buyer receives the big one.

If the seller said that he sold the small one and the buyer does not know, he only receives the small one.

If the buyer says the big one and the seller says the small one, the seller must swear that he sold the small one.

If both of them say that they do not know, they divide it.

(Gemara) - R. Yochanan: This Mishnah is written to rule unlike Sumchus who says that in all cases of doubt, they divide it.

R. Ila: You could establish that each of them claimed with certainty.

Question (R. Yosi): If it is a case when both of them claim with certainty, could you say that R. Yochanan said that the Mishnah is written to rule unlike Sumchus? (R. Yochanan was assumedly talking about doubtful claims!)