What are the three things forbidden during bein hashmashot between Yom Tov rishon and Yom tov sheni? Thanks
R’ Akiva Eiger in Nedarim 69B and OC 495:1 famously wonders if it is permitted to cook during bein hashmashos even to eat immediately since the cooking could be on one day and the eating on the next.
In the Haggadah Bais Halevi (1:p275) it says that R’ Chaim Brisker didn’t allow smoking during bein hashmashos for the same reason. The inhale might be on one day and the exhale (enjoyment) is the next day.
In the sefer Yom Tov Sheni Khilchoso (1:21) he brings from R Shlomo Zalman and R Elyashiv that doraisas shouldn’t be done, but drabbanan are ok.