Ulla: There are three cases in which the end was permitted in order to encourage the beginning of that thing. 1. Skins before the treaders (048). 2. The shutters of stores (51). 3. Returning the bandage on a plastered wound on Shabbos or Yom Tov in the Mikdash.Rechava quoting Rabbi Yehuda: Another one should be added: 4. One who opens his keg or begins a dough on the Regel for the purpose of Yom Tov. This is in accordance with Rabbi Yehuda (053) who said “he may finish”.
Challenge: ‘2. Shutters’ is explicitly stated by the Mishnah (51)?
Resolution: One might think Beis Hillel permits this because “there is no ‘construction’ or ‘destruction’ in keilim” and other doors would be permitted as well, this is why Ulla explains that “the end was permitted in order to encourage the beginning” [although we actually do hold that there is no construction regarding keilim, here we are talking about large keilim which have the appearance of actual construction].
Challenge: ‘3. Bandaging in the Mikdash’ is also explicitly mentioned?
Resolution: One might think this is permitted because “there is no ‘shevus’ in the Mikdash” [this is not an absolute rule, but in general the takkanos of the Chachomim were not applied in the Mikdash so as not to conflict with the established ancient institutions] and even Kohanim not presently involved in avodah would be permitted, this is why Ulla explains that “the end was permitted in order to encourage the beginning”.
Challenge: ‘4. Opening a keg’ is also explicitly stated? “One who opens a keg of wine or begins a dough in honor of the Regel. Rabbi Yehuda: He may finish it. Chachomim: He may not finish it.”
Resolution: One might think that there is no tumah on an am ha’aretz during the Regel, and even an unopened keg touched by an am ha’aretz during the Regel is permitted as well, this is why Ulla explains that “the end was permitted in order to encourage the beginning”.
Question: Why didn’t Ulla count #4?
Response: He talks only about unanimous things but this is a machlokes.
Challenge: #1 and #2 are also only the opinion of Beis Hillel?
Resolution: Beis Shammai versus Beis Hillel is not considered an opinion at all [At Yavneh it was decided that it was too perilous to maintain the two schools of Hillel and Shammai, and the opinions of Beis Shammai were erased entirely and it is forbidden even to be stringent and follow their views].
Our Mishnah runs counter to this Tanna: Beraisa (a): Rabbi Shimon ben Elazar: Beis Shammai and Beis Hillel agree that the shutters may be removed, they only argue about returning the shutters. Beis Shammai forbids it, while Beis Hillel permit it. Additionally, Beis Shammai only forbid it when the shutters have hinges, but when there are no hinges, everyone agrees it’s permitted [even to return the shutter].
Challenge: There’s another Beraisa (b): The debate is only when the shutters have no hinges, but when there are hinges, everyone agrees it’s forbidden! 
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