וְדִלְמָא אָתֵי לְעַשּׂוּרֵי מִן הַחִיּוּב עַל הַפְּטוּר, וּמִן הַפְּטוּר עַל הַחִיּוּב!

And that ordinance could lead to a problem, as perhaps he will come to tithe from produce that requires tithing by Torah law for produce exempt from tithing by Torah law and from produce exempt from tithing by Torah law for produce that requires tithing by Torah law. By Torah law, the produce is not ownerless and requires tithing. However, due to the ordinance, people might relate to it as ownerless produce and assume that one is exempt from tithing it. Alternatively, they will erroneously conclude that the obligation to tithe from that produce is by rabbinic law and will tithe produce from it that one is exempt from tithing by Torah law, or they will tithe that produce from produce that one is exempt from tithing by Torah law. The result will be produce that is not properly tithed, as one may tithe produce that one is obligated to tithe by Torah law only from other produce that one is obligated to tithe by Torah law.

דְּאָמְרִינַן לֵיהּ: כִּי מַעַשְׂרַתְּ – עֲשַׂר מִינֵּיהּ וּבֵיהּ.

The Gemara answers: That problem will not arise, because if the declaration of ownerless status is retracted after three days, we say to the person who ultimately takes possession of the produce: When you tithe, tithe from that produce itself. In that way, the above problem does not arise.

מֵיתִיבֵי: הַמַּפְקִיר אֶת כַּרְמוֹ, וְלַשַּׁחַר עָמַד וּבְצָרוֹ – חַיָּיב בְּפֶרֶט וּבְעוֹלְלוֹת וּבְשִׁכְחָה וּבְפֵיאָה, וּפָטוּר מִן הַמַּעֲשֵׂר.

The Gemara raises an objection from a baraita : One who declares his vineyard ownerless, and at dawn he arose and picked grapes from the vineyard, is obligated in the mitzva of leaving individual fallen grapes left for the poor [ peret ], and in the mitzva of leaving incompletely formed clusters of grapes for the poor [ olelot ], and in the mitzva of leaving forgotten sheaves, and in the mitzva of pe’a , produce from the corner of the field or vineyard, as the obligation to separate those gifts from the poor is incumbent upon the one who harvests the field (see Leviticus 19:9–10). And he is exempt from the obligation to separate the tithe from the grapes. Because the vineyard is ownerless, there is no obligation to tithe the produce.

בִּשְׁלָמָא לְעוּלָּא – דְּרַבָּנַן קָתָנֵי לָהּ, וּדְאוֹרַיְיתָא קָתָנֵי לָהּ. אֶלָּא לְרֵישׁ לָקִישׁ, אַמַּאי פָּטוּר מִן הַמַּעֲשֵׂר?

The Gemara asks: Granted, this is so according to Ulla, who explained that the Rabbis taught the previous baraita and explains that although the Sages instituted that the ownerless status does not take effect completely until three days have passed, by Torah law it takes effect immediately, and that this baraita is taught in accordance with Torah law. That is the reason that one is exempt from tithing the grapes. However, according to Reish Lakish, why is he exempt from separating the tithe? Until three days after the declaration, neither by Torah law nor by rabbinic law does ownerless status take effect.

אָמַר לָךְ: כִּי אֲמַרִי אֲנָא – לְרַבִּי יוֹסֵי, הָא – רַבָּנַן הִיא.

The Gemara answers that Reish Lakish could have said to you: Although when I explained the first clause and the latter clause of that baraita I said that both are in accordance with the opinion of Rabbi Yosei, who said that an ownerless item leaves the possession of the owner only when it enters the possession of another, this baraita is in accordance with the opinion of the Rabbis, who hold that it leaves the possession of the owner immediately upon the declaration of ownerless status.