When the Gemora answers that the Tanna of the Braisa is the Tana of Litra D'Ktziot, why does the Gemora (or at least Rashi) continue to explain that we're talking about a Beitza of a Treifa? Since that Tanna holds that a Davar She'bminyan is not Batil even B'Drabonon, wouldn't it make more sense to revert back to a Beitza that was laid on Yom Tov so that it's consistent with the beginning of the Braisa?
Thanks,
Kol Tuv, Yossi
This is an interesting question. I have not yet found anyone who asks it, so I will try and answer from Sevara.
1) I should point out that when Rashi writes that the Beraisa is referring to the Beitzah of a Tereifah, he was really forced to do so by the Gemara itself, because the Gemara answers that the Tana of Litra Ketzi'os maintains that a Davar sheb'Minyan is not Batel in a thousand, even if the prohibtion is mid'Rabanan, and certainly not if the prohibition is mid'Oraisa. When the Gemara refers to an Isur d'Oraisa, it is clearly referring to the Beitzah of a Tereifah, which is why Rashi was forced to write this.
2) My initial idea to answer your question was to suggest that indeed the Gemara did revert to the case of the Beitzah born on Yom Tov. The main purpose of the Gemara is not to tell us that a Beitzah of a Tereifah is not Batel in a thousand, but rather, Rav Papa's main answer is to tell us that the Beraisa maintains that even an egg born on Yom Tov, since it is an item which is counted, is not Batel even in a thousand. After the Gemara had reverted to the case of the egg born on Yom Tov, it merely added that certainly the Beitzah of a Tereifah is not Batel in a thousand, but this is indeed obvious since we now know that even an Isur d'Rabanan is not Batel in a thousand.
3) However, I retracted from my initial idea. It is in fact crucial that the Gemara continues to say that we are talking about the Beitzah of a Tereifah, because otherwise we cannot explain why the Beraisa says that the Safek Beitzah is forbidden. If we would only be referring to a d'Rabanan prohibition, any case of doubt should be permitted. This is indeed the reason why the Gemara was forced in the first place to answer that the "Sefeikah Asurah" part of the Beraisa is referring to the Beitzah of a Tereifah, since if it indeed was born from a chicken which is a Tereifag, is a Torah prohibition. Therefore, if there is a doubt about whether or not it was born from a Tereifah chicken, we also must be stringent.
4) So even though the part of the Beraisa that states that if the forbidden egg became mixed with another thousand it remains forbidden can now be explained to refer to an egg born on Yom Tov, nevertheless the part of the Beraisa that comes before this -- that the doubtful egg is forbidden (without a situation in which it became mixed with others) -- must be referring to the egg from a chicken which might have been a Tereifah.
Dovid Bloom