OUR MISHNAH IS R. MEIR
(Gemara) Question: Who is the Tana of the Mishnah?
Answer: It is like R. Meir. It is unlike R. Yehudah, who does not distinguish "Korban" from "Ha Korban."
(Seifa): If he said "l'Korban, I will not eat from you" it is permitted.
Contradiction (Mishnah #1 - R. Meir): If one said "l'Korban (is) what I will not eat of yours", he is forbidden;
(R. Aba): He means "what I eat from you is like a Korban, therefore I will not eat from you."
Question: In Mishnah #1 he said "l'Korban". In our Mishnah he said "l'Korban", i.e. Lo Korban, it is not like a Korban. (R. Meir does not infer the positive from the negative.)
EXPLAINING THE MISHNAH
(Mishnah): If one said "Shevu'ah, I will not eat of yours," "Ha Shevu'ah she'Ochel of yours," or "Not a Shevu'ah, that I will not eat of yours," he is forbidden.
(Gemara) Inference: "Ha Shevu'ah she'Ochel" means that he will not eat.
Contradiction (Mishnah #2): There are two Shevuos (of Bituy explicit in the Torah for which one who transgresses brings a Korban. In all, there are four: she'Ochel, that I will not eat, that I ate, and that I did not eat.
This shows that "she'Ochel" means that he will eat!
Answer #1 (Abaye): It can mean either, depending on the circumstances;
If he was being pressured to eat, and he said "I will eat, I will eat, and Shevu'ah she'Ochel", he means that he will eat;
If he said "I won't eat, I won't eat, and Shevu'ah she'Ochel", he means that he will not eat.
Answer #2 (Rav Ashi): The Mishnah should say that he said "Ha Shevu'ah she'Iy Ochel (I will not eat)."
Objection: If so, obviously he may not eat!
Answer: One might have thought that he wanted to say she'Ochel, and he mispronounced it she'Iy Ochel. (Normally, people say she'Lo Ochel, and not she'Iy Ochel).
Abaye did not answer like Rav Ashi, because the Mishnah did not say "she'Iy Ochel".
Rav Ashi did not answer like Abaye because "that I will not eat" can also mean two things (and the Mishnah should have explained this also);
If he was being pressed to eat, and he said (incredulously) "I won't eat?! I won't eat?!", whether he swore "I will eat" or "I won't eat", he it means that he will eat.
"Shevu'ah that I will not eat" can also mean that he will not eat (when he was not pressured).
Rather, the Tana made a firm rule. "I will eat" means he will eat. "I won't eat" means he won't (regardless of the context).
THE STRINGENCY OF NEDARIM OVER SHEVUOS
(Mishnah): This is (the previous Mishnah) is a stringency of Shevuos over Nedarim;
A stringency of Nedarim over Shevuos is that if one said 'Konam Sukah, I will not make one' or similarly regarding Lulav, or Tefilin, he is forbidden. Such a Shevu'ah does not forbid, for one cannot swear to override Mitzvos.
(Gemara) Question: Saying that a Shevu'ah is more stringent implies that such a Neder takes effect, but it is weaker. The Mishnah (15b) totally permits ('Korban, I will not eat from you')!
Answer: Our Mishnah refers to oaths not to sleep, speak or walk (15b). Such a Neder takes effect mid'Rabanan (15a, 1:c).
SHEVUOS AGAINST MITZVOS
(Mishnah): A stringency of Nedarim over Shevuos...
(Rav Gidal citing Rav or Shmuel): The source that one cannot swear to transgress a Mitzvah is "Lo Yachel Devaro." One may not profane his own word, but he may for the sake of Hash-m's desires (His word).
Question: Presumably, "Neder la'Shem Lo Yachel" teaches that even if a Neder opposes a Mitzvah, he may not profane it;
The same should apply to Shevuos, for it says "Shevu'ah la'Shem Lo Yachel"!
Answer #1 (Abaye): A Neder forbids (objects, e.g.) Hana'ah (pleasure) from a Sukah. There is no obligation on a Sukah (Tosfos; Rosh - it does not look like he uproots the Mitzvah from himself). A Shevu'ah forbids himself to benefit from (text of Tosfos, Ran - sit in) a Sukah. (He may not uproot his obligation to do a Mitzvah!)
Objection (Rava): Fulfillment of Mitzvos is not considered Hana'ah! (A vow not to get Hana'ah from a Sukah would not forbid the Mitzvah.)
Answer #2 (Rava): A Neder forbidding sitting in a Sukah takes effect, but a Shevu'ah not to sit in a Sukah does not (like above, (d). Ran - we must say that the Neder forbade the Sukah, regarding sitting in it, Sitting is not tangible!)
Question: We learn that one cannot swear to transgress a Mitzvah from elsewhere!
(Beraisa) Suggestion: Perhaps if one swore to transgress a Mitzvah and did not do so, he is liable.
Rejection: "To do evil or good" - just like doing good refers to something optional, also doing evil. This excludes one who swore to transgress a Mitzvah and did not do so, for this is not left to his whim.
Answer: This verse exempts from a Korban (for transgressing Shevu'as Bituy). "Lo Yachel" exempts from a Lav.