(Mishnah): If a person is invited to his friend for a meal and he doesn't trust him to separate Maaseros, he should say before Shabbos, "Whatever I will separate tomorrow shall be (1/10th of the) Maaser and what is around it should be the other 9/10th. But whatever I made Maaser should be the Terumas Maaser for the rest of the Maaser and its Maaser Sheni should be on its northern or southern side and it should be redeemed onto coins.

(Gemara) (R. Yochanan): The Mishnah is referring to Demai, but if it is definite Tevel, it may not be done.

Question: But there is a Mishnah (later in this Perek) that allows it even for definite Tevel - If a person had Tevel figs in his house and he was in the Beis Midrash or in the field...(he may make a stipulation)...? You cannot say that it is discussing Demai, as the latter part of that Mishnah explicitly teaches Demai...?

Answer: Did R. Yochanan teach that the Mishnah discusses Demai and not definite? He only said that it is more suitable for Demai (although it is still valid for definite).

What's the difference between Demai and definite Tevel? For Demai, a person may stipulate on something that he doesn't possess; for definite Tevel, it is only if he possesses it.

R. Yannai made a stipulation on definite Tevel. He asked R. Chiya the Great about making this stipulation on Shabbos. R. Chiya answered him from a pasuk that discusses Maaser (Devarim 14:23), "...in order that you shall learn to fear Hash-m your G-d all of the days'' - (Maaser may be taken) even on Shabbos (which is achieved by making a stipulation before Shabbos and then actually separating on Shabbos).

Question #2 (R. Yannai): What was the significance of my seeing a tax collector's staff hanging from me in a dream?

Answer (R. Chiya the Great): In the future you will be in a position of power over Jews.

R. Hoshiya had made a stipulation on definite Tevel. There was a woman in his area who had cooked her Tevel vegetables before Shabbos and forgotten to tithe. On Shabbos she came to R. Hoshiya asking what to do. R. Hoshiya used his own stipulation to appoint Zavdi ben Levi to tithe for her (by separating Maaseros from R. Hoshiya's own vegetables).

Question (R. Ba bar Mamal): Didn't Zavdi bar Levi need to acquire the vegetables for R. Hoshiya before being able to tithe them?

Question (R. Zeira): What exactly was the case? If his stipulation included others, he would not have needed to acquire the vegetables beforehand; and if his stipulation was only for his own produce, then Zavdi would have needed to acquire the vegetables for R. Hoshiya. (Since he didn't, this shows that R. Hoshiya's stipulation included others.)

(R. Yaakov bar Zavdi citing R. Abahu disagrees): The question was asked and the answer was that Zavdi did not acquire for R. Hoshiya.

(R. Yannai): A person must remember his stipulation when he comes to separate on Shabbos.

(Shimon ben Vava citing R. Yochanan): He must repeat his stipulation when he comes to separate.

Question (R. Remiya to R. Zeira): Isn't he doing an act of Tikun (fixing) on Shabbos (if he repeats it)?

Answer (R. Zeira): It's permitted since he already stipulated.

Question (R. Yirmiyah to R. Zeira): Isn't it forbidden because he is wasting food (meaning that he must waste the Terumas Maaser that he separates, rather than leave it with the Am HaAretz who might eat it)...?

Answer (R. Zeira): He doesn't destroy it; he merely crumbles it into small pieces that the Am HaAretz won't eat.

Question (R. Yirmiyah to R. Zeira): Isn't he tithing from that which was given to him by his host as food, which is a form of theft?

Answer (R. Zeira): The Am HaAretz is assumed to agree to his guest tithing.

The words of Rabbanan disagree with this, as R. Shmuel bar Yitzchak said that Rebbi and R. Yosi bei R. Yehuda were guests of a certain host. Someone went and spoke disparagingly to the host and said, "Keep your eyes on them and you'll see that (they are tithing your food, because) they suspect you of not tithing. The host sat and studied their actions and they were throwing small pieces of food one to another, in the form of a game (as a facade to their tithing). Why wasn't he happy that they were tithing for him?

Answer: He was happy, but didn't want them to suspect him.

Question: The Mishnah taught that there is a stipulation that one can make. A Baraisa teaches that R. Yehuda disagreed and did not allow the stipulation. Why did he say this? Can a person stipulate about something not in his possession? However, R. Yehuda agrees that a guest may go and buy produce from the same place that his host bought and then tithe from what he bought. But how could a person tithe for something that is not his?

Answer (R. Abahu citing R. Yochanan): They viewed him like one who sells Tevel fruits to his friend. (in a case where there is no choice, Chazal allowed a person to separate from his produce for his friend...)

Proof (Tosefta): If a person sold Tevel produce to his friend, he must chase after him to tithe. If he didn't find him, if he knows that some of the fruit still exists, he should tithe for them (from his own produce). And if not, he does not need to tithe for them. If he is doubtful if some still exists, he should tithe for them (Terumas Maaser) and declare the rest of the Maaser on his friend's fruits. (This proves that if necessary, one may declare another person's fruits to be Maaseros.)