Answer: (Really, witnesses do not cause publicity.) There, the buyers caused their own loss. (Had they researched well, they would have found out about the sale.)

Question: Did Rav really say that one who bought without a document may collect from sold property?!

(Mishnah): One who lent money with a document may collect from sold property; if he lent without a document, he only collects from unsold property. (The laws of a sale and a loan should be the same, it depends whether or not witnesses publicize things.)

Suggestion: Perhaps Rav argues with the Mishnah, for he is a Tana.

Rejection (Rav and Shmuel): One who lent money without a document may not collect from heirs or from sold property.

Answer: Loans and sales are different.

A person borrows discreetly (and asks the witnesses not to publicize it), lest his property decline in value (if people would know that he needs money);

A person announces when he sells land, so that potential buyers will hear.

(Beraisa): If Reuven used a field for a year, and his son used it for two years, or vice-versa, or each used it for a year and a buyer used it the third year, this is a Chazakah.

Inference: One who buys from an heir can make a Chazakah.

Contradiction (Beraisa): Shimon used (what was Muchzak to be) Levi's field for three years, uncontested. Levi died after the first or second year. If Levi's son Kehas (who stood to inherit the field) did nothing, or he sold it one year after Levi's death (and the buyer was quiet in the third year), Shimon has a Chazakah.

If one who buys from an heir can make a Chazakah, we must say that there is publicity to a sale. If so, when Kehas sold it, this should be considered a Macha'ah!

Answer (Rav Papa): The Beraisa discusses when Kehas wrote a document selling all his fields. (Shimon did not know that he contests the field, therefore it was not a Macha'ah.)

(Mishnah): Craftsmen, partners, sharecroppers, and overseers cannot make a Chazakah (in property they work on, share or oversee);

A man cannot make a Chazakah in his wife's property, nor vice-versa. A father cannot make a Chazakah in his son's property, or vice-versa.

This refers to Chazakah to prove ownership;

Locking the fence, fencing or breaching any amount in a wall is a Chazakah to acquire a gift, to divide an inheritance, or to acquire Hefker property.

(Gemara - Shmuel's father and Levi): The Mishnah does not mention a craftsman. We learn (that he cannot get a Chazakah) from a Kal va'Chomer from a partner.

(Shmuel): The Mishnah says that a craftsman does not get a Chazakah, but a partner may.

This is like Shmuel taught elsewhere.

(Shmuel): A partner can make a Chazakah against his partner, he can testify for him (we shall explain when), and he is considered a Shomer Sachar when watching the common property.

Question (R. Aba): Did Shmuel really say that a partner can make a Chazakah?!

Contradiction (Shmuel): A partner is like one who uses another's field with permission.

Suggestion: This teaches that he cannot make a Chazakah.

Answer #1 (Rav Yehudah): Shmuel's teachings apply to two different cases, when he makes a Chazakah in the entire property, and when he makes Chazakah in half (and claims that they agreed that he will receive this half).

This can be understood either way.

Version #1: A Chazakah in the entire property is valid. One would not allow his partner to use the entire field for three straight years. Surely he sold his share;

A Chazakah in half the property is invalid, for it is normal for each partner to use the same half for several years, and then they switch.

Version #2: A Chazakah in the entire property is invalid, for it is normal for a partner to let the other use the entire field for three years, and then he will get it for three years;

A Chazakah in half the property is valid. Had they not divided, and they wanted to share the fruits every year, they would work the entire field together.

Answer #2 (Ravina): In both cases he made a Chazakah in the entire property;

If the field is destined to be divided (it is big enough for each to get a field of proper size), the Chazakah is valid, for one would not allow his partner to use the entire field for three straight years;

If the field is not destined to be divided, the Chazakah is invalid. It is normal to allow a partner to use the same half for several years, and then switch.

(Shmuel): A partner is like one who uses another's field with permission.

Question: If Shmuel's Chidush is that he cannot make a Chazakah, he should say this explicitly!

Answer (Rabah bar Avuha): He teaches that he receives Peros that are Magi'a l'Kesafim (Rashbam - ready to harvest; R. Tam - they came through exertion).