The 3rd perek of Eruvin - beginning with a mishnah that ranges many topics. A joined meal to establish an eruv, also for Eruv Techumin (to extend one's city environs by another 2,000 amot). What about a meal made on maaser sheni?! You sell that produce, and use that money down the road (I'm Jerusalem). [What's What: They cycle of maaser sheni and maaser ani in the shemittah cycle]. What about someone who swore off food? That oath doesn't include water or salt, by definition. Note that establishing an eruv can made over wine, even if the person to use the eruv is a Nazir, who can't have wine (that's fine), or a Yisrael over terumah (machloket). And extending the techum through a "beit ha-pras" (when you don't know where the bodies are buried) - a kohen can go through to eat the eruv meal, in between the graves... The Gemara on the textual formula of the mishnah, instead of its content: Don't take the text too literally, when it comes to a statement of "all" - even when it gets more precise, to make exceptions. The example here is positive time-bound commandments from which women are exempt (except for when they're not) - and the inverse as well (the positive non-time-bound commandments from which women are also exempt). But the notion that the Gemara would treat the language of the mishnah as less than precise is very surprising. Perhaps the question really is what counts for food for the seudah that makes an eruv. What about brine (which is neither salt, nor water, but both, and more of a good than either alone). The Gemara gives us the key manner of deriving interpretation: mi'ut ribui mi'ut. Amplification and specific restrictions... And amplification again. Likewise, klal u-prat u-klal. The logic may not be intuitive (or second nature!), but as long as you're relying on one of the accepted methodologies, you're set.