Rif Yomi Video Edition -- Beitza Daf 5

beitza 2b

{Beitza 5a}
Rabba said: From the edict of Rabban Yochanan ben Zakkai and on, an egg {laid on the first day of Rosh haShana} is permitted on the second day of Yom Tov of Rosh haShana. {Ran: There was an edict that they did not accept witnesses that the day was Rosh haShana from mincha and on, but rather they concretized the assumption that the next day was Rosh haShana. Yet since the majority of the first day had passed in holiness, it was decreed that the rest of the day also should be treated with holiness. When the Temple was destroyed, Rabban Yochanan ben Zakkai decreed that they could accept testimony all day long, since the cause for the original edict, of messing up the song of the day, was inapplicable. With Rabban Yochanan ben Zakkai's edict in place, there is no longer a single holiness to the day. Thus, it stands to reason, says Rabba, that an egg laid on the first day of Rosh haShana is permitted on the second, since there are two seperate kedushot, and one of the two days is there just because of safek, just as by other Yamim Tovim.}
For they learned {in a Mishna}: Once the Temple was destroyed, Rabban Yochanan ben Zakkai established that they should accept the testimony of establishing the month all day {thus overturning the initial edict}.

Abaye said to him {Rabba}: But Rav and Shmuel both say that an egg is forbidden.
And we answer: this is no question. This is for us and that is for them. {Ran: That is, it is a Bavel/Eretz Yisrael distinction. To explain, for the residents of Bavel, nothing changed with the edict of Rabban Yochanan ben Zakkai, since they did not accept testimony at all in Bavel, and so they always did not know, there was no overt difference before and after the edict. But for the peolpe of Eretz Yisrael, since they see the difference, they will know why it is permitted, and so it is permitted.}

{Beitza 5b}
And we conclude: Rava said: Even after the edict of Rabban Yochanan ben Zakkai,


beitza 3a

{Beitza 5b continues}
an egg is forbidden {on the second day}. For would Rabban Yochanan ben Zakkai not admit that if witnesses come from michna and on, they treat both that day and the next day as holy? {For the edict was only in terms of counting from each day, but the holiness aspect of it stuck as with the original edict.} Thus, it is clear that they have a single holiness, and an egg would be forbidden on both of them {the days of Rosh haShana}.
And we derive from this that residents of Eretz Yisrael are required to make two days of Yom Tov of Rosh haShana.