When yom tov is next to Shabbat... Making one eruv going to the west, and another one going to the east. From there, he follows the procedure for two days of eruv. When can he leave the eruv in the direction he's walking? And what if he ate the eruv on the first day? He won't have an eruv on the second day, because it's been eaten! Does that have implications for the holiness of the day? The significance of whether the two different days have one blended holiness, or are they separate? This discussion takes on a life of its own, as it were, in exploring the opinions of "the four sages" - who certainly appear to conclude that there are two holinesses between Shabbat and yom tov. Until the Gemara raises a question, swaps their opinions, and then raises a more intense question on those switched opinions. Including a question on whether the sages were presenting views, in the abstract as possible opinions, or what they themselves actually believed (what a can of worms that could open). R. Hisda tries to figure out Rav's view on the holinesses, alas without R. Huna to consult. Should there be other sources to answer this question directly, rather than sussing out the logic?