In a case where Reuven and Shimon both claim that the ship or the field over which they were arguing belonged to their respective fathers, too - Rav Nachman rules - 'Kol de'Alim G'var'.

If Reuven and Shimon both produce separate Sh'taros stating that Levi had gave each of them the same gift on the same day, Rav rules 'Yachloku' - Shmuel, 'Shuda de'Dayna', which means that it is up to the Beis-Din to decide to whom the donor really meant to give it (see also Tosfos DH 'Shuda de'Dayna').

He declines to learn like Rav - because whereas according to Rav, we are definitely not complying with Levi's wishes, according to him, there is a good chance that the Beis-Din will in fact, give it to the one to whom Levi had in mind to give it.

'Shuda' really means - 'to cast', as if to say that the Beis-Din will throw the article to the rightful owner.

It will make no difference if one of the Sh'taros was written in the morning, and the other one, in the afternoon - since it is not customary to insert the time in a Sh'tar. Consequently - a Sh'tar always takes effect only at the end of the day (except for those written in Yerushalayim, where the Minhag was to write the time of day).

The reason that ...

... Rav and Shmuel rule 'Yachloku' or 'Shuda de'Dayna' there is - because seeing as the two Sh'taros are exactly the same and were given on the same day, and that it is consequently impossible to discover to whom Levi wanted to give the field, Beis-Din prefer to arbitrate in one way of the other, whereas ...

... Rav Nachman rules 'Kol de'Alim G'var in our case, because, since each claimant may be able to bring proof that he is the owner of the ship, Beis-Din prefer to let them fight it out until one of them does so.

We know that Levi did not hand one of the two recipients the Sh'tar a day or two before the other (negating what we just said about being impossible to arrive at the correct conclusion) - because we assume that Levi gave the Sh'taros to the recipients on the same day that he wrote them.

In the case in the Mishnah in Bava Kama where Reuven swapped a cow for Shimon's donkey, or if he sold him his Shifchah, and it is later discovered that the cow or the Shifchah had previously given birth, the Safek is - whether they gave birth before the transaction or after it.

The Tana refers specifically to ...

... swapping in the case of the cow and the donkey - because one cannot acquire an animal with money; and had the Kinyan consisted of Meshichah, then they would have seen whether the baby was born at that stage or not.

... selling in the case of the Shifchah - because one can acquire her through Kinyan Kesef (and presumably, that is how one would normally acquire her). Consequently, she need not have been present when the Kinyan took place; Hence the Safek.

The Tana rules there - 'Yachloku' ...

... a Kashya on Rav Nachman, who rules in the previous case 'Kol de'Alim G'var'.

We know that the Kashya from 'ha'Machlif Parah ba'Chamor' is a Kashya on Rav Nachman and not on Shmuel (who ruled erlier 'Shuda de'Dayna') - because if we do not ask it in Kesuvos, which is the major Sugya that discusses Rav and Shmuel's Machlokes, then it would be unlikely to ask it here (where it is only brought in the form of a Kashya).

Shmuel does not rule here too 'Shuda de'Dayna' - because that ruling only applies there, where it is a matter of whom the donor had in mind to give it, but not when it is a question of when a certain event occurred (see Maharsha).

To answer the Kashya on Rav Nachman, we differentiate between the two cases, inasmuch as despite the fact that there, like here, a. neither is Muchzak in the cow or the Shifchah (because, as we ascertain elsewhere, the Tana is speaking when they were in a public meadow at the time), and b. it is possible to ascertain (through witnesses) exactly when they gave birth - nevertheless, unlike in the case of the ship or the field (which belonged to one of the disputants but not to the other), the cow and the Shifchah belonged both to each of the litigants at different stages, giving them a sort of Chazakah (and we are only uncertain as to at which stage they gave birth).

Rebbi Chiya cites a Beraisa 'Gazlan shel Rabim Lo Sh'meih Gazlan', which the Neherda'i apply to Rav Nachman's case ('Zeh Omer shel Avosai, ve'Zeh Omer shel Avosai') - inasmuch as he stole from two people, neither of whom, for all we know, may have been the rightful owner.

Rav Ashi disagrees. According to him, there is no way that the Gazlan, who does not have a claim, will be allowed to keep the ship or the field. And he inteprets the Tana's statement ('Gazlan shel Rabim Lo Sh'meih Gazlan') to mean - that he cannot fulfill his obligation of returning it, since he does not know to whom to return it.

According to him - Rebbi Chiya is also referring to a storekeeper whose weights and measures were false, and who now decides to do Teshuvah.

Rebbi Aba rules that if Reuven the Me'arer (who protests at Shimon's Chazakah of his field) subsequently loads a basketful of fruit (from tSAhat field) on to Shimon's back - it substantiates Shimon's Chazakah, and the latter acquires the field immediately ('I Dali leih Ihu Gufei Tzana de'Peira, Le'altar Havi Chazakah').

Rabeinu Chananel explains 'I Dali leih Ihu Gufei Tzana de'Peira' to mean - 'If Shimon presents Reuven with a gift of a basketful of fruit, which he accepts'.

The fact that Reuven helped Shimon to load the fruit will not be instrumental in establishing the latter as the owner - if Reuven backed up his action with the claim 'le'Peiros Horadtiv' (I authorized him to take the fruit as an Aris).

On the other hand, his claim of 'le'Peiros Horadtiv' will not help him - after three years, once Shimon's Chazakah is complete.

The problem with the current ruling is - that (bearing in mind that, as we explained earlier, it is not customary to write a Sh'tar for Peiros) seeing as Reuven cannot claim 'le'Peiros Horadtiv' after three years, if he really did give Shimon the Peiros for three years or more, how will he able to safeguard himself against Shimon establishing a Chazakah on the field and claiming that it is his?

To answer this Kashya, we cite the case of Mashkanta de'Sura, where we have the same problem - because, since Shimon has the right to eat the Peiros for five or ten years, who is to then stop him from making a Chazakah?

And we resolve it - by advising Reuven to make a Mecha'ah to the effect that Shimon only has rights over the fruit, but not over the field (which is a valid Mecha'ah, despite the fact that he simultaneously concedes partial rights to Shimon).

The reason that we need to come on to Mashkanta de'Sura to answer the first Kashya is - because Mashkanta de'Sura is a Takanas Chazal, in which case we need to justify the Chachamim instituting a Takanah that will lead to the owner losing his field.

Mashkanta de'Sura is not a case of Ribis (despite the fact that, in the case of a bumper harvest, the creditor will eat far more fruit than the value of the loan) - because there is an equal chance that, following a year of draught, the field will only yield a Dinar's-worth even though he lent him ten Manah for ten years (a Manah per year).

Chazal did not include Nochrim in the Din of Chezkas Shalosh Shanim - because most Nochrim are Gazlanim, and people are therefore afraid to make a Mecha'ah when a Nochri is being Machzik their property.

When Rav Yehudah Amar Rav talks about 'Yisrael ha'Ba Machmas Akum', he is referring to - a Yisrael who purchases a field (which is known to have previously belonged to a Yisrael) from a Nochri and who then establishes a Chazakah on it.

And he rules - that such a Chazakah is ineffective.

We query Rava's initial statement that if the Machzik claims that the Nochri informed him that he bought the field from the Me'arer, he is believed, in that - it is impossible for the Machzik who claims that the Nochri informed him that he bought the field from the Me'arer, to be believed - seeing as we would not have believed the Nochri himself.

What Rava really must have therefore said was - that if, after establishing his Chazakah, he claims that the Nochri actually purchased the field from the Yisrael in his presence, he is believed ...

... because he has a 'Migu' (that he could have said that he himself purchased it from him.

The Halachah will be even more lenient where the Machzik claims that he purchased the field from a Yisrael (who bought it from the original owner) - because then, all he would need to claim is that he saw the Yisrael working on it for one day.