Nedarim 11B

תניא: ״חולין״ ״החולין״ ״כחולין״, בין ״שאוכל לך״ ובין ״שלא אוכל לך״, מותר. ״לחולין שאוכל לך״⁠ — אסור. ״לחולין לא אוכל לך״⁠ — מותר.

It is taught in a baraita: If one declares food: Non-sacred, or: The non-sacred, or: Like the non-sacred, then whether he combines that expression with the phrase: That which I eat of yours, or: That which I do not eat of yours, he has not expressed a vow and the food remains permitted. However, if he says: That which I eat of yours should be considered laḥullin, i.e., not non-sacred, but rather consecrated, the food is forbidden. If he says: That which I do not eat of yours should be considered laḥullin, the other individual’s food remains permitted to him.

רישא מני ⁠— רבי מאיר היא, דלית ליה מכלל לאו אתה שומע הין.

The Talmud analyzes this baraita: Who is the author of the first clause of the baraita? It is R' Meir, who does not hold that from a negative statement you can infer a positive statement. Consequently, even if one said: That which I do not eat of yours should be considered non-sacred, that does not indicate that what he does eat should be considered consecrated.

אימא סיפא: ״לחולין לא אוכל לך״⁠ — מותר. והתנן: ״לקרבן לא אוכל לך״⁠ — רבי מאיר אוסר. וקשיא לן: הא לית ליה מכלל לאו אתה שומע הין?

However, say the latter clause of that baraita: If one says: That which I will not eat of yours should be considered laḥullin, the other individual’s food remains permitted to him. But didn’t we learn in a Mishnah (13a) that if one says: That which I will not eat of yours should be considered lakorban, R' Meir prohibits him from eating food belonging to the other individual? Lakorban apparently means la korban, it is not an offering. The reason for this opinion is that his statement indicates that what he does not eat is not an offering, but what he does eat should be considered an offering. This poses a difficulty for us because R' Meir does not hold that from a negative statement you can infer a positive statement.