Gemara

(Rav Asi citing R. Yochanan): If he measured and put it in a Simta (a shoulder of Reshus ha'Rabim), he acquires.

(Rav and Shmuel): The buyer's Kelim acquire for him everywhere, except for in a Reshus ha'Rabim;

(R. Yochanan and Reish Lakish): They acquire even in a Reshus ha'Rabim.

(Rav Papa): They do not argue: Rav discusses a proper Reshus ha'Rabim, and R. Yochanan discusses a Simta. He calls it a Reshus ha'Rabim, for it is not a Reshus ha'Yachid.

Support (R. Avahu citing R. Yochanan): The buyer's Kelim acquire anywhere he is allowed to place them.

Inference: They do not acquire where he may not place them (i.e. a Reshus ha'Rabim).

85b - Question (Rav Sheshes): Does a buyer acquire with his Kelim in the seller's premises?

Answer #1 (Rav Huna - Mishnah): If a man threw a Get into his wife's garment or basket (in his premises), she is divorced.

Objection (Rav Nachman): Many rejected that proof! The case is, the basket was hanging on her, or it was tied to her but dragging on the ground, or it was between her legs, or he sells baskets, or a man allows his wife to use the place of her garment and basket. (Therefore, we cannot learn to a regular case.)

86a - Answer #2 (Ravina): Rav and Shmuel taught that the buyer's Kelim acquire for him everywhere (except for in a Reshus ha'Rabim).

Suggestion: 'Everywhere' includes the seller's premises!

Rejection (Rav Ashi): The case is, the seller told him to acquire. (It is as if the seller lent his premises to the buyer in order to acquire.)

Rishonim

Rif: Rav Huna answered Rav Sheshes that the buyer's Kelim acquire in the seller's Reshus only if the seller said 'acquire in this way.' Some say that Ravina tried to learn from Rav and Shmuel, who taught that the buyer's Kelim acquire for him everywhere, i.e. even in the seller's premises. Rav Ashi rejected this; there, the seller told him to acquire.

Rosh (5:15): In Rav Ashi's rejection, we say that the seller acquired his premises to the buyer to enable him to acquire. The Chidush is that it helps to lend the Reshus for this through mere words. Normally, a loan or rental of land requires money or Chazakah. In order that the land will acquire without Kelim, one must truly acquire the land. This is why Chachamim rented R. Gamliel's land to acquire tithes (Kidushin 27a). To enable the buyer's Keli to acquire, it suffices for the seller to give permission. I did not find any text like the Rif says.

Rosh (ibid): Rav Asi said in the name of R. Yochanan that if he measured and put it in a Simta, he acquires. Rav Papa does not require that he measured! Rav Papa discusses when the seller said 'go acquire.' Also in a joint Reshus, the buyer's Kelim acquire only if he measures or the seller says 'go acquire'. This is not needed in the buyer's Reshus, for this is no worse than Meshichah.

Tosfos (85a DH Kol): Measuring helps like saying 'go acquire.' The two teachings of R. Yochanan teach the same thing. Perhaps he said only one, and the other was derived from it.

Beis Yosef (CM 200 DH Kosav): The Rif and Rambam hold that Rav Asi discussed a typical case. He did not mean that he acquires only if he measured.

Beis Yosef (DH v'Heilach): Later, the Rif brings Rav's law that what was measured out acquires, i.e. in a Simta, or in the seller's Kelim in the buyer's Reshus. This contradicts what he said that the buyer's Kelim do not acquire in the seller's Reshus unless the seller said 'go acquire'! Perhaps measuring helps like 'go acquire.' Or, saying 'I sell a Se'ah for a Sela' is like saying 'go acquire', and this helps also for the seller's Kelim in the buyer's Reshus, unlike R. Yonah.

Rambam (Hilchos Mechirah 4:1): One's Kelim acquire anywhere he may put them. Once the Metaltelim are in the Keli, neither can retract. It is as if Hagbahah was done or they were put in the buyer's house. Therefore, one's Kelim do not acquire in Reshus ha'Rabim or in the seller's Reshus, unless the seller said 'go acquire in this Keli.' Similarly, if one acquired the Keli first and lifted it, then put it in the seller's Reshus, and later bought the Peros, once they are in the Keli he acquires them. Since the seller benefits from the sale, he is not particular about the place (that the buyer's Keli occupies).

Poskim

Shulchan Aruch (CM 200:3): One's Kelim acquire anywhere he may put them. Once the Metaltelim are in the Keli, neither can retract. It is as if Hagbahah was done or they were put in the buyer's house. Therefore, one's Kelim do not acquire in Reshus ha'Rabim or in the seller's Reshus, unless the seller said 'go acquire in this Keli.' Then, he acquires if it is in the seller's Reshus.

SMA (9): The Shulchan Aruch rules like the Rif and Rambam, that he definitely does not acquire.

Shach (7): In the seller's Reshus, the buyer's Keli acquires also if he received permission to put the Keli there.

Rema: Some distinguish and say that if it is not the buyer's Reshus, rather, a Simta or something similar, his Kelim acquire only if he measured or he said 'go acquire.'

SMA (8): This means that the seller measured and put in the buyer's Kelim in a Simta. If the buyer measured, he acquired through this even without his Kelim, for he did Meshichah.

Shulchan Aruch (4): Similarly, if one acquired the Keli first and lifted it, then put it in the seller's Reshus, and later bought the Peros, once they are in the Keli he acquires them. Since the seller benefits from the sale, he is not particular about the place.

Gra (15): We must say that he lifted it, for if not, it is still the seller's Keli.

Question (Bedek ha'Bayis): The Tur cited this in the name of the Ri mi'Gash. He brought the Ramah, who said that lending the Reshus helps only if he says 'go acquire.' Why did the Tur say that they disagree? They discuss different laws!

Answer (Bach 8 DH u'Mah): The Ramah holds that 'go acquire' helps, but lending the Reshus does not. The Ri mi'Gash holds oppositely, that 'go acquire' helps only because this shows that he lent the Reshus to him!

Beis Yosef (DH v'Ein): Rav Dimi rejected the proof from Gitin by saying that her husband sells baskets. Rashi explains that he has a house for baskets, therefore he is not particular about the place of her basket. The Rambam and Ri mi'Gash hold that he sold the basket to her, therefore, hnc for its place. The Magid Mishneh says that even though the conclusion is like R. Yochanan, that no man is concerned for the place of his wife's basket, we learn about other cases from Rav Dimi.

Shulchan Aruch (EH 139:9): If a man threw a Get into his wife's basket in his Reshus, she is not divorced, for her Keli acquires in his Reshus only if he is not particular about its place.

Taz (12): The Ran says that in Gitin, we resolved that the buyer's Keli does not acquire in the seller's Reshus. The Beis Yosef said that it is a Safek, for the Gemara did not explicitly resolve this. He should have said here in the Shulchan Aruch that it is a Safek, like he says in Sa'if 10!

Beis Shmuel (14): These are the words of the Rambam. The Rambam holds that we settled the question; the buyer's Kelim do not acquire in the seller's Reshus. She is not even Safek divorced. However, the Shulchan Aruch (Sa'if 10) says that she is Safek divorced! Also here, he means Safek divorced. We cannot distinguish Get from Kinyan. The SMA said that the Shulchan Aruch rules like the Rambam. This is wrong.