989. Yom Kippur is Just Like Shabbos

Shvisas Asor 1:2

All forms of labor for which one would be liable to the penalty of stoning on Shabbos render one liable for kareis (spiritual excision) if performed on Yom Kippur. Anything that obligates one to bring a sin offering on Shabbos likewise obligates one to bring a sin offering if performed on Yom Kippur. Anything that is prohibited to do on Shabbos, even if it is not a prohibited form of labor, is likewise prohibited on Yom Kippur. If one performs such an action, he is punished with the lashes administered for acting rebelliously, the same as for such activities when performed on Shabbos. Whatever may not be handled on Shabbos may likewise not be handled on Yom Kippur. Whatever may not be said or done on Shabbos is similarly prohibited on Yom Kippur. The general principle is that there is no difference between Shabbos and Yom Kippur except that one who intentionally performs a prohibited form of labor on Shabbos is liable to the penalty of stoning, while one who does so on Yom Kippur is liable to kareis.

Shvisas Asor 1:3

One is permitted to trim a vegetable on Yom Kippur from the mid-afternoon on. Trimming a vegetable means removing the wilted leaves and cutting the rest in order to prepare the vegetable for eating. It is similarly permitted to open nuts and pomegranates on Yom Kippur starting in the mid-afternoon so that one will not encounter difficulty later on (by having to prepare labor-intensive foods after the fast). When Yom Kippur falls on Shabbos, it is prohibited all day to trim vegetables and to open nuts and pomegranates. The universal practice in Babylonia and North Africa is not to do these things on Yom Kippur at all. Rather, Yom Kippur is treated like Shabbos in all such details.