R. Yochanan vs. R. Akiva, on what elements of the inauguration of the Mishkan were essential,and whether any of those elements could have been cut, and the Mishkan still be valid. One key question being why this gets attention, given that it was a one-time event and there's no reason to think it will be repeated. Also, how did Moshe dress Aharon and his sons (which seems a comparable after-the-fact kind of question)? How did Moshe belt them?