Shabbat 40 and Shabbat 40b, about the development of the prohibition against bathing or going to a sauna on Shabbat, for fear of heating water on Shabbat, and then the idea of warming up water rather than cooking it, whether oil is considered cookable, and the difference between a keli rishon, the item in which food was heated on the fire, and keli sheni, the container into which cooked food was transferred.
