Why can't one cook for the second day of Yom Tov on the first day? Why won't something along the lines of Eiruv Tavshilin help in this case as well?
1 Answer
The format of a 2-day Yom Tov is a s'feika d'yoma. If Thursday is the Yom Tov, I cannot cook for Friday which is Chol (Rosh Hashana isn't exactly because of the same reason, but the same answer would apply).