Bernard Dickman asked:
RH20a- Rav Acha says that Yom Kippur can not come adjacent to Shabbos. Ulla agrees and adds that Yom Tov (Rosh Hashanah and Succos) also can not fall on Friday or Sunday.
Is the argument between them whether Rosh Hashanah can fall on Sunday (it would seem that they should both know such a factual issue) or are they disagreeing as to the reason why RH can't fall on a Sunday?
The Kollel replies:
The Gemara is discussing the time before the calendar was fixed. The question was not factual, but rather whether the Chachamim changed the day on which they established Rosh Chodesh in order for Rosh Hashanah not to fall on Sunday.
D. Zupnik