Beitzah 17 - No food mix
We learned that when a Holiday (Yom Tov) falls out on a Friday, one is allowed to cook for the needs of the Yom Tov, but not for the Shabbat right after it. However, if one leaves a little food over from Thursday (called "eruvei tavshilin)- then cooking for Shabbat becomes permitted.
What if one did not create this food eruv? - Then he is forbidden to cook for Shabbat. What about his flour, is it also forbidden? But why do we ask? - For the case when others would want to help him out and bake with his flour for him, can they use the flour? - The answer is that they cannot, but rather, they have to receive from him the ownership of this flour, and then they can cook for him with that flour, because is now theirs.
What if he disregarded the prohibition and cooked anyway, can this be eaten? The Talmud tries to derive the answer from various similar rulings. For example, we know that one is allowed to cook for himself for Yom Tov, and if some food is left over for Shabbat - that is fine. However, he should not use this device as a loophole. Can we assume that when he deliberately violates the prohibition of eruv, it is worse than a loophole, and is certainly prohibited? - No, we cannot. Perhaps the Sages were stricter with loopholes than with deliberate violations. On so on, two more attempts, but the question remains unresolved.
Art: The Cooks by Theodule Augustine Ribot