The Gemara describes two talmidei chachamim teaching the Kohen Gadol about the avoda on Yom Kippur. Why two? Is this some type of testimony that it requires two. (Why not three, a typical number for courts?)
As always, thank you for your wonderful help.
This is not testimony that it requires two, nor is it a judicial procedure which would require three people. Rather, the Talmidei Chachamim are the Sheluchim of Beis Din, and since they represent the Beis Din, it is a show of honor to send two people.
Alternatively, perhaps they sent two people in order for the Kohen Gadol to constantly be learning about the Avodah. While one teacher teaches, the other has a chance to rest. That way, the chances of a mistake being taught are much less probable.
It is interesting to note that the Mishnah later (18a) does not mention how many were sent to teach the Kohen Gadol; it just says, "Zekeinim m'Ziknei Beis Din." Also, the RAMBAM (Hilchos Avodas Yom ha'Kipurim 1:5) makes no mention of how many were sent. The RASHASH on the Mishnayos (Yoma 1:3) questions why it was left out. Perhaps the Mishnah holds that the number "two" is Lav Davka, and the Gemara here mentions two only because that was a normal number to send to the Kohen Gadol.
The gemara in Chagiga uses this logic when discussing teaching maisa Merkava... :-)
The gemarah in Chagiga is talking about the amount of students. Maaseh Merkavah I think can only be taught Beyuchid Arayos can be taught to a maximum of two, so that while one talmid asks his Rebbe, the other one must listen so he will be clear about what his Rebbe says, while if there were three, than while one asks, the other two may learn themselves and miss an issur and think that it's really muttar.
(a) TOSEFTH HAROSH answers that if the kohen gadol will change they will "TESTIFY" that they gave him the halachas of the ketoret and he can not denie this 'testimony'
(b) look TOSEFETH YESHANIM -"TOV HASNOYIM MIN AHECHAD" TWO IS BETTER THAN ONE
- ALWAYS A PLEASURE TO RECEIVE YOUR INSIGHTS
Thank you very much for pointing that out! (Tosfos Yeshanim may indeed mean that two teachers are better than one, as we pointed out.)