Explanation: We are thinking that the reason R. Yosi forbids in our Mishnah is like R. Yochanan, who said above (43a) that Hefker is like a gift. Until it comes to the Reshus of one who acquires it, it does not leave the Reshus of the Mafkir. This is why he said that the Reisha is Rabanan, and the Seifa is R. Yosi;

According to this, the entire Beraisa is fine. The Reisha teaches that all three days, he can retract, due to swindlers, like I explained;

From now (three days) and onwards, letter of the law he cannot retract, for Rabanan hold that from the time that one was Mafkir something, it left his Reshus.

Explanation (cont): The Seifa teaches that if he said "this field is Hefker for one day", in such a case there is no concern for swindlers. If at the time he was Mafkir it he intended to acquire it back immediately, why would he be Mafkir it for a set time?

He should be Mafkir it totally, since he intends to acquire it back immediately. He gets nothing [advantageous through limiting his Hefker]!

Rather, surely for that time that he was Mafkir it, he resolved and was Mafkir it without scheming at all. Therefore, once one acquired it, whether he or someone else, he cannot retract. This is fine even according to Rabanan.

Distinction: However, this that it taught that until one acquired it, whether he or someone else, he can retract, this is like R. Yosi, who holds that until it enters the Reshus of one who acquired it, it does not leave the Reshus of the Mafkir;

According to Rabanan, since they say that it left his Reshus, how can he retract?!

Observation: Indeed, when it taught according to R. Yosi that until one acquired it, whether he or someone else, he can retract, this is not only for Hefker for a set time, like the cases of the Seifa. Even for permanent Hefker, i.e. the Reisha, he can retract until someone acquired it;

However, for the law that once someone acquired it, he cannot retract, Hefker for a time is unlike permanent Hefker, like I wrote. [Since] it needed to teach [Hefker] for one day or one week, it taught also in that case "until someone else acquired it."

Question: It taught that once he acquired it, he cannot retract. I.e. it was Hefker even according to R. Yosi, and it is exempt from Ma'aser. Why is this fine?

Since R. Yosi holds that Hefker, until it enters the Reshus of one who acquired it, it does not leave the Reshus of the Mafkir, it turns out that when he acquired it again, he acquired from himself, and not from Hefker, for it never left his Reshus!

Answer: We can say that granted, R. Yosi holds that until it enters the Reshus of one who acquired it, it does not leave the Reshus of the Mafkir. Even so, just like if someone else acquired it, he acquired from Hefker, and not from a gift, since it was possible for another (anyone else) to acquire it...

Also now that he himself acquired it explicitly through the law of Hefker, and not Stam, lest we attribute this to retraction [from his Hefker], it is called that also he acquired from Hefker, since he still did not retract, and someone else could have acquired it.

There is no difference between him and someone else. Therefore, if the Reisha is Rabanan and the Seifa is R. Yosi, we can establish the Mishnah properly.

Question: [The Gemara asks that] this is astounding, that the Tana taught [Stam] according to two Tana'im!

Answer: This is why Ula answers and says that also the Seifa is Rabanan. The reason is, until someone acquired it, be it he or someone else, he can retract, because seven years and a week are different, for they are not common.

Explanation: I.e. people are not normally Mafkir in this way. Since he deviated, we assess his intent;

Since he did not want to be Mafkir it permanently, and he is still tied to it even in that time for which he was Mafkir it, he does not want it to leave his Reshus until someone else acquires it.

Therefore, Rabanan hold regarding Hefker for a set time, what R. Yosi holds regarding permanent Hefker.

Conclusion: The Seifa is properly like Rabanan, like we established it according to R. Yosi, for regarding Hefker for a time, they do not argue.

Implied question: We asked that if so (the Reisha is R. Yosi), why can't he retract after three days?

Answer: This is lest the law of Hefker be forgotten. I.e. letter of the law, according to R. Yosi even after three days he can retract;

The reason [Chachamim said that he cannot] is because if you will say so (that he can retract), people will come to say that even when he did not retract, and someone else acquired, he did not acquire from Hefker;

Since before he acquired, the Mafkir was able to retract, this shows that it was in his Reshus. It turns out that the other person did not acquire from Hefker. Rather, he received a gift.

[People] will think that it must be tithed, and they will come to separate tithes from elsewhere to exempt it, which is from Chayav (what is obligated) on Patur (what is exempt), or they will tithe from it to exempt other Peros, which is from Patur on Chayav! (Both of these are invalid.)

Therefore, they enacted that after three days he cannot retract, so that mid'Rabanan it is [unmistakably] Hefker.

Gemara: If so, even from the first day it should be Hefker!

Explanation: I.e. we should have enacted that even from the first day it is Hefker, for this reason itself! What is the difference between within three days and after three days?

Explanation: I.e. even from the beginning they are Mafkir only in order to retract. It turns out that their Hefker is not Hefker. It is only a ruse;

Therefore, all three days they stood their words on Torah law (it is not Hefker). However, after three days there is no concern, like I explained above (43b Sof DH Tanya).

Implied question: We needed this reason "due to swindlers" also at the beginning of our Sugya, when we established the Reisha like Rabanan, like I explained above!

Answer: Since now we are more meticulous about the Reisha, to enable establishing it like R. Yosi, we also explain [now] the reason;

Indeed, just like we need [this reason] according to R. Yosi, in order to leave the law like Torah law, we need it also according to Rabanan, in order to depart from Torah law and enact.

Explanation: We challenge "from now and onwards, he cannot retract." Granted, letter of the law, according to R. Yosi he can retract and it is not Hefker. [However,] Rabanan enacted that it is Hefker.

Surely, they obligated it in Ma'aser, since mid'Oraisa it is not Hefker;

Granted, they could have exempted it due to Hefker Beis Din Hefker. Even so, Chachamim did not come to be lenient and uproot from Ma'aser, what the Torah obligates!

Therefore, there is concern lest people come to tithe from Chiyuv on Patur!

One who acquired it will say "surely, since Chachamim gave to me what I acquired, it was total Hefker. His (the Mafkir's) retraction, letter of the law it had no effect;

Chachamim obligated me to tithe only mid'Rabanan, due to a decree due to onlookers who heard his retraction and thought that it was a retraction, and [really] it has no effect. If this were so (his retraction were valid), how did Chachamim give to me his Hefker?!"

He will come to tithe from this [produce], which he thinks is Patur [because it was truly Hefker] on something that is Patur by the letter of the law, e.g. wheat that grew in a flowerpot without a hole.

He thinks that both of these are [Chayav] mid'Rabanan. This is wrong. What he acquired is Chayav mid'Oraisa. Since letter of the law, the Mafkir's retraction helped, it turns out that he did not acquire from Hefker;

When he tithes from these Peros on those from the flowerpot without a hole, this is tithing from Chiyuv on Patur.

Implied question: We could have asked "perhaps he will come to tithe from Patur on Chiyuv", i.e. from Peros of a flowerpot without a hole on this (that he took from "Hefker")!

Note: In our texts, the Gemara asks both of these questions. The Ran's text asked only about Chayav on Patur. (PF)

Answer: The Gemara asked one [of the two questions it could have asked].

Observation: Our answer answers all the questions.

Gemara: We tell [him] "when you tithe [what you took from 'Hefker'], tithe from it itself";

Explanation: I.e. do not tithe from it on elsewhere, and not from elsewhere on it. Rather, tithe from it itself.

Gemara: They asked, a Beraisa teaches that if one made his vineyard Hefker and promptly harvested it, he is obligated in Peret, Olelos, Shichechah and Pe'ah.

Explanation: Even though Hefker is exempt from all of these (gifts for the poor), like we say (Shabbos 68a) 'Nishmar' exempts Hefker...

Even so, because in all of them, an extra "Ta'azov" is written, he is obligated in them whenever he took back possession. So it says in Bava Kama (94a).

Gemara: And he is exempt from Ma'aser.

Explanation: Since there is no extra "Ta'azov" written about Ma'aser, there is no difference between him and someone else; he is exempt.

Gemara: It is fine for Ula. Rabanan taught [the Beraisa]. It teaches the Torah law.

Explanation: I.e. even though Rabanan enacted that within three days, he can retract, and therefore when he acquires it, he is obligated in Ma'aser mid'Rabanan....

Even so, this is fine according to [Rabanan]. It says Patur, i.e. mid'Oraisa, but mid'Rabanan, indeed, he is obligated.

Explanation: [We ask that] he establishes the other Beraisa like R. Yosi. How can this [Beraisa] be like [R. Yosi]?

According to R. Yosi, since he says that according to letter of the law, a Mafkir can retract until it comes to the Reshus of one who acquires it...

... When he promptly harvested (the vineyard that he made Hefker), why is it exempt? Since he did not specify that he acquires from Hefker, we should say that he retracted. It turns out that he harvested his own, and not from Hefker!

Implied question: (Why is this difficult?) R. Yosi holds that also he (the Mafkir) can acquire via the law of Hefker, from what he himself made Hefker!

Answer: That is when he specified [that he acquires from Hefker]. However, if he harvested Stam, since he can retract, [perhaps he retracted, and] he harvests his own!

Gemara: [Reish Lakish] tells you, I said like R. Yosi. This is like Chachamim.

Explanation: Granted, the other Beraisa he establishes totally like R. Yosi. You are forced to say that this [Beraisa] is Rabanan, and not R. Yosi.