Near the top of Beitzah 9a, Avuah DeShmuel says that Challo may not be separated on Yom Tov EVEN FROM dough kneaded on Erev Yom Tov - what is the "Afilu"?!
I would have thought that Challo might be able to be separated from dough made on Yom Tov (since could not have separated it before Yom Tov) but not from dough kneaded on Erev Yom Tov (since could have and should have separated it before Yom Tov). It sounds from the "Afilu" that Challo may not be separated from a Yom Tov dough, and not even from an Erev Yom Tov dough - how is this explained?!
Meir Eliezer Bergman, Manchester UK
The simple explanation of the "Afilu" is that Avuha d'Shmuel is negating Rabah's comment that one may separate Chalah on dough kneaded on Erev Yom Tov. The "Afilu" is that even though this is a Yom Tov "knead" (pun intended) which was done close to Yom Tov, Chalah may not be separated on Yom Tov (Rashi DH "Ain Mafrish" clearly states that Avuha d'Shmuel agrees one may take Chalah from a Yom Tov dough). [For an added aspect of Chidush on Avuha d'Shmuel's statement, see the Rashba.]
All the best,