(a) Is the chashash that the gemarah refers to of shecting an animal and finding it to be a teriefah simply dependent upon the regulra rules of safek deoraytah lechumra and rov and chazaka or are there some other dictating factors and rules specific to the issue of tzorech yom tov.
(b) Also, it seems that rashi learns that is one shechts an animal and then finds it to be not kosher, in essence he violated an issur on yom tov, would not the same apply if one were to cook a meal and it turns out that noone eats a certainn dish b/c of the selection of other dishes, does the cookers act become a violation of yom tov?
Yehuda Frogel,
(a) If the Gemara had to do with the laws of Rov and Chazakah, why do the Amora'im argue whether or not we say "she'Tzarisch l'Badkan"? All agree to the rules of Rov and Chazakah! In addition, why does the Gemara assume that shingles and a Behemah she'Ritzetzah must be identical? Perhaps there is more chance of Chilul Yom Tov by one than by the other?
It seems clear that there is no "Rov" to assume that the animal is a Tereifah, there is only a Re'usa. The same seems to be the case with shingles. The question is whether one is required to take such a Re'usa into consideration when it might result in an Isur Yom Tov, if worse comes to worst.
(b) This would not apply to cooking a meal which nobody eats. In the case of the Gemara, the person had reason to presume at the time of his Melachah that some Chilul Yom Tov might result from his Melachah, since there already was a Re'usa. This is not the case when one serves a meal; there is no Re'usa. Since the act of cooking was permitted, it can never become "retroactively prohibited."
In addition, due to the rule of "Ho'il," any food cooked on Yom Tov cannot violate an Isur d'Oraisa, even if the guests for which it was prepared do not eat it.
M. Kornfeld