Gemara

82a (Rav Dimi citing R. Yochanan): If Reuven told Shimon 'do Meshichah on this cow (take it to your premises), but it is not yours until 30 days from now', 30 days later he acquires it, even if it is in a swamp.

Contradiction (Ravin citing R. Yochanan): The cow is not acquired 30 days later.

Answer: Rav Dimi discusses when he said 'acquire from now.' In Ravin's case, he did not say this.

86b - Question (Rami bar Chama): If her husband gave her Get and said 'you are not divorced until 30 days from now' and she left the Get in Tzidei (the side of a) Reshus ha'Rabim (and it was still there at the end of 30 days), what is the law?

Version #1 - Answer #1 (Rav Chisda): We learn from Rav and Shmuel that she is not divorced (because it is not considered her Reshus. A Get must be put "b'Yadah", into her hand or Reshus).

(Rav and Shmuel): Seizure of orphans' property helps only if the property is in a Reshus ha'Rabim.

Tzidei Reshus ha'Rabim is like a Reshus ha'Rabim.

Answer #2: Just the contrary, we learn from Rav Nachman that she is divorced!

(Rav Nachman): If Reuven told Shimon 'be Moshech this cow, but it is not yours until 30 days', he acquires it then, even if it is in a swamp.

Suggestion: A swamp is like Tzidei Reshus ha'Rabim.

Rejection: No, a swamp is different.

Version #2 - Answer #1 (Rav Chisda): We learn from Rav Nachman that she is divorced;

A swamp is like the side of Reshus ha'Rabim.

Answer #2: Just the contrary, we learn from Rav and Shmuel that she is not divorced!

Suggestion: Tzidei Reshus ha'Rabim is like a Reshus ha'Rabim.

Rejection: No, they are different.

Bava Metzi'a 34a - Version #1 (Rava): When one gives an animal to a Shomer Chinam, it is as if he stipulated 'if it will be stolen and you will want to pay, it is acquired to you from now.''

Version #2 (Rava): It is as if he stipulated 'if it will be stolen and you will want to pay, it is acquired to you just before it is stolen.'

These versions differ about when it was in a swamp just before it was stolen.

Rishonim

Rambam (Hilchos Mechirah 2:9): If Reuven told Shimon 'do Meshichah on this cow, but do not acquire it until after 30 days' and he did Meshichah, he did not acquire.

Ra'avad: If the cow is in the buyer's Reshus on day 31, he acquires. This is like one who says 'you are Mekudeshes to me after 30 days.' It takes effect on that day.

Magid Mishneh: Here is different. If it were the same, the cow would be acquired even if it was in Reshus ha'Rabim! Rather, since he did not day 'from now', he cannot acquire through Meshichah, for it ceased.

Rambam (ibid.): If he said 'acquire from now and after 30 days' he acquired it, even if it is in a swamp on day 30. This is like one who acquires on Tanai; the Tnai was fulfilled and the sale is valid.

Magid Mishneh: 'Swamp' refers to a Reshus that does not belong to the buyer. The same applies if it is in a Reshus ha'Rabim; the Gemara merely gave a typical example. A swamp is a place to graze.

Rebuttal #1 (of Magid Mishneh - Kesef Mishneh): The Gemara requires it to be in a swamp! R. Yochanan holds that Kidushin 'from now and after 30 days' does not finish until 30 days (Kidushin 60a). This is why he requires the cow to be in a swamp at the end of 30 days, a place where one can acquire.

Rebuttal #2 (Lechem Mishneh): The Rambam rules like the second version, in which we equate a Get without 'from now' to Meshichah with 'from now'. Surely, a Reshus ha'Rabim does not suffice. All the more so it is not enough according to the first version, which holds that Tzidei Reshus ha'Rabim is better than a Reshus ha'Rabim! Perhaps the Magid Mishneh explains that the Rambam considers 'from now' to be like a Tanai, therefore we do not care where the cow is. The Gemara proves otherwise.

Defense (Beis Shmuel EH 146:1): R. Yochanan holds that the Kinyan 'grows', and is completed after 30 days. Therefore, the cow must be in a swamp at this time. The Rambam rules that 'from now and after 30 days' is a Tanai.

Rosh (9:15): Rav Nachman taught that if Reuven told Shimon 'do Meshichah on this cow, but it is not yours until 30 days from now', 30 days later he acquires it, even if it is in a swamp!

Hagahos Ashri (8:13:3): R. Yochanan taught that Meshichah of a cow to acquire after 30 days works even if it is in a swamp, but not if it is in Reshus ha'Rabim. The Ri says that this is when he said 'from now'. If not, he does not acquire.

Ra'avad (cited in Ran 45b DH Garsinan): The question of a Get left in Tzidei Reshus ha'Rabim, and Rav Nachman's Halachah of Meshichah of a cow, are when he said 'from now and after 30 days.' He was forced to say so because he holds that without 'from now', even if she found the Get there are picked it up, it would be Pasul due to 'Tli Gitech me'Al Gabei Karka', i.e. her husband did not give it to her. Also, if Rav Nachman discusses without 'from now', the cow would not be acquired, like we learned above (82a).

Rebuttal (Ran): We hold (Kidushin 59b) that 'from now and after 30' is a Safek. 'After 30' could be a Tnai (if I will not retract within 30 days), or a retraction (from 'from now'). If our Sugya held that it is a Tanai, it would not matter where the Get or cow was later! Rather, it is a retraction. It is as if he never said 'from now'. This shows that the question is about one who said only 'after 30' (unlike the Ra'avad). A Get is valid if it never left her Reshus. We learn from Rav Nachman, who taught that the cow is acquired after 30 days even if he did not say 'from now', i.e. in the swamp is like in his Reshus. He acquired through the initial Meshichah, since it is still in his Reshus.

Defense (Mordechai Kidushin 526): Surely, regarding Meshichah to acquire 'from now and after 30 days', we have no Safek about a retraction. The Safek is only regarding Kinyan Kesef, which works without 'from now'.

Rambam (Hilchos Gerushin 9:2,3): A man gave a Get and said 'you are divorced only 30 days from now.' If she left it in Tzidei Reshus ha'Rabim and it was stolen or lost after 30 days she is divorced, since the Get was intact on the day of divorce and she designated it in a place that is not Reshus ha'Rabim.

Rashba (cited in Ran 46a DH ul'Inyan): Rami bar Chama and Rav Chisda hold that Rav Nachman discussed without saying 'from now'. We do not hold like them. If he did not say 'from now', he did not acquire (82a). To establish Rav Nachman like the Halachah, we must say that he said 'from now'.

Rebuttal (Ran): Above, the Gemara said that without 'from now', he does not acquire. This was according to R. Yochanan. It was not the Gemara's conclusion. Therefore, since Rami bar Chama and Rav Chisda hold that Rav Nachman discussed without saying 'from now', we hold like them. Even without 'from now', the purchase and Get are valid.

Defense (Ba'al ha'Ma'or Gitin 37b): The difference between the two versions of Rava (Bava Metzi'a 34a) is when the animal was stolen from a swamp. I.e. it is acquired in this case only if he said 'from now.'

Lechem Mishneh: Rashi explained that regarding gifts we are not in doubt whether 'from now and after 30 days' is a Tnai or retraction. Rather, he gives the item itself now, and the Peros after 30 days.

Poskim

Shulchan Aruch (CM 197:7): If Reuven told Shimon 'do Meshichah on this cow, but it is not yours until after 30 days', and he did Meshichah, he did not acquire. If he said 'acquire from now and after 30 days', he acquires, even if it is in a swamp. It is as if he acquires it from now on Tanai, and the Tnai was fulfilled.

Beis Yosef (DH mi'Kol): R. Yerucham says that if it was in Reshus ha'Rabim, it is a Safek. I do not know why he calls this a Safek.

SMA (17): All the more so he acquires if the cow is in a Reshus owned by the buyer exclusively or in partnership with the seller. If it was in the seller's Reshus or Reshus ha'Rabim, 'Al Menas' would be required

Gra (171:9): In EH (40:4), the Shulchan Aruch is concerned for R. Yochanan's opinion that 'from now' does not help because it means that he leaves his acquisition incomplete. The Rambam and Shulchan Aruch (CM 197:7) say that Meshichah to acquire 'from now and after 30 days' works even if the cow is in a swamp. It cannot be in Reshus ha'Rabim. The Magid Mishneh says that it can be. This is like the Ramban (Sefer ha'Zechus 44b) and Rashba, who rule unlike the Sugya on 86b. The Ramban is consistent with his ruling (regarding Kidushin) unlike R. Yochanan. The Ran is a third opinion. He holds that Meshichah works if it is still in a place where one can acquire, even if he did not say 'from now'.