We learned: Shabbos and Yom Tov that are contiguous: Rav: An egg born on one is forbidden on the following day. Rabbi Yochanan: It is permitted on the following day.
Question: Does Rav hold that contiguous days carry one Kedusha? Rav said: The Halacha follows Four Zekeinim who ruled like Rabbi Eliezer that two contiguous days are considered separate Kedushas.
Response: The debate between Rav and Rabbi Yochanan is about something different entirely. Rav holds of Hachana D’Rabbah* [as explained in 004, that Yom Tov may not prepare for Shabbos or vice versa], while Rabbi Yochanan does not.
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* Tosfos: Challenge: Hachana means when the egg is fashioned on a Holy Day - for instance when Yom Tov is on a Sunday and the egg is laid on that day, the problem is that the egg was fashioned the day before, on a Holy Day, Shabbos. But in our case, the egg was fashioned friday and laid on Shabbos, why should it be forbidden now on Sunday?
Resolution 1: Its laying is also a Hachana, for an egg is not prepared if it hasn’t been laid.
Resolution 2: Since it would become permissible on Sunday due to its having been laid on Shabbos, it may be considered “prepared on Shabbos” for Yom Tov.