Nedarim 14A

לאו אתה שומע הן! ואלא רבי יהודה, היינו רישא!

a negative statement you can infer a positive statement? How then can it be inferred that it should be like an offering? And if it is rather the opinion of R' Yehuda, who disagrees with R' Meir in this matter, the ruling of the Mishnah is superfluous, as this is identical to the ruling of the Mishnah in the first clause. The Mishnah above (10b) already established that a vow that uses the term laḥullin takes effect.

איידי דקתני ״כבשר חזיר״, ״כעבודה זרה״, להכי קתני ״חולין״.

The Talmud answers: The ruling is superfluous. However, since the Mishnah teaches that the vow does not take effect when he says that the food will be like pig meat or like an object of idol worship, it therefore teaches incidentally that this ruling also applies when he says that it will be non-sacred.

רבינא אמר: הכי קתני, ואלו מותרין: ״כחולין״, ״כבשר חזיר״, ״כעבודה זרה״. ואי לא תנא חולין, הוה אמינא בעי שאלה.

Ravina said that this is what the Mishnah is teaching: And these are the vows that do not take effect at all and therefore the item mentioned in the vow remains permitted: One who said that a certain item will be like non-sacred food, or like pig meat, or like an object of idol worship. And if it did not teach the case of non-sacred food, I would say that although the vow does not take effect, it still requires, by rabbinic law, a request to a halakhic authority for its dissolution.

ומי איכא לאסוקי על דעתא הכי? הא מדקתני סיפא: האומר לאשתו ״הרי את עלי כאימא״⁠ — פותחין לו פתח ממקום אחר, מכלל דרישא לא בעיא שאלה! אלא מחוורתא, חולין ממילא נסבה.

The Talmud asks: But is there any reason to consider this interpretation? But from the fact that the latter clause teaches with regard to a man who says to his wife: You are hereby to me like my mother, that dissolution is broached with him by suggesting a different extenuation, it may be inferred that the vow in the first clause does not necessitate a request to a halakhic authority. Rather, the interpretation of Ravina must be rejected, and it is clear that the case of non-sacred food was cited tangentially to the other cases in the Mishnah.